Dennis Brennecke Katrin Knickmeier Iwona Pawliczka Ursula Siebert Magnus Wahlberg *Editors*

# Marine Mammals

A Deep Dive into the World of Science

Marine Mammals

Dennis Brennecke • Katrin Knickmeier Iwona Pawliczka • Ursula Siebert • Magnus Wahlberg *Editors*

# **Marine Mammals**

A Deep Dive into the World of Science

*Editors* Dennis Brennecke Kieler Forschungswerkstatt, Kiel University and Leibniz Institute for Science and Mathematics Education Kiel, Germany

Iwona Pawliczka Prof. Krzysztof Skora Hel Marine Station, Faculty of Oceanography and Geography University of Gdansk Hel, Poland

Magnus Wahlberg Marine Biological Research Center University of Southern Denmark Kerteminde, Denmark

Katrin Knickmeier Kieler Forschungswerkstatt, Kiel University and Leibniz Institute for Science and Mathematics Education Kiel, Germany

Ursula Siebert Institute for Terrestrial and Aquatic Wildlife Research University of Veterinary Medicine Hanover, Foundation Büsum, Germany

Horizon 2020 Framework Programme (710708) Results incorporated in this standard have received funding from the European Union's Horizon 2020 research and innovation programme under the grant agreement No. 710708.

Cover photo: Hèloïse Hamel

ISBN 978-3-031-06835-5 ISBN 978-3-031-06836-2 (eBook) https://doi.org/10.1007/978-3-031-06836-2

© The Editors and the Authors 2023. This book is an open access publication.

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### **Preface**

Science is fun, interesting, challenging and engaging. Science makes it possible to discover the marvels of the natural world. With science, we can document the lives of seals and whales, diving to great depths in pursuit of their prey and yearly travelling vast distances between breeding and feeding grounds. Science is also what makes airplanes fy and trains run. And, in the long run, science is what makes us humans able to survive on Earth, in spite of the rapidly increasing human population and the challenges we face due to environmental degradation, climate change and pandemics.

As scientists, we are engaged and full of joy when speaking about our work. Some people call us the 'last truly religious people on the planet'. We love our work, and sincerely believe that science can change the world for the better.

In spite of all the virtues of science, we predict a shortage of scientists in many western societies in the future. We will not only need more people doing research, but also engineers, technicians, veterinarians and medical doctors. There seems to be a general lack of enthusiasm among young people in taking up the challenge of studying natural science which paves the road to an interesting, challenging and fascinating future with relatively well-paid and attractive jobs.

Why is that? The major problem may be the way we try to inspire young people in choosing their career. There is a long way from the enthusiastic 'mad scientists' you meet at universities, to the rather dry presentation of science in many secondary and high school textbooks. Even though modern science centres and media platforms are doing a great job to inspire visitors and viewers to learn about research, more tools are needed to catch the interest of the next generation in science.

Marine mammals easily arouse the interest of students. They are sentinel species in many of the current debates about environmental issues: they are affected by fsheries, plastics in the oceans, environmental pollutants, anthropogenic noise and climate change. Understanding how marine mammals are affected by human activities opens up exciting discussions around many different scientifc disciplines, such as biology, chemistry, physics and oceanography.

The book is written to be an inspiration and guide for teachers to expand their way of teaching biology and other natural sciences in secondary and high schools. The book is also intended for students to learn more about the natural world. We have collected a series of topics, all related to current research in marine mammals, with focus on species found in the Baltic and North Sea. We hope that whales and seals will work as a portal to entice students to become interested not only in marine mammals and marine biology, but also in animal conservation and nature protection, and many other scientifc topics.

The book is divided into chapters covering topics such as marine mammal biology, sound and hearing, plastics, pollutants and fsheries. Each chapter introduces the topic and gives important background facts that the teacher can use in introductory presentations. At the end of each chapter, there is a small section of current hot topics in marine mammal research that can be used to spur the interest of students when seeing themselves as future scientists with all the excitement such work brings. Finally, we suggest several teaching modules that can be directly implemented in hands-on activities, inside as well as outside the classroom. At the end of a book is a glossary, explaining many of the specialized and perhaps unfamiliar words used in the chapters. Other words, that are not explained but that we expect the reader may have to look up in e.g., Wikipedia, are indicated in italics.

This book is the result of the EU H2020-funded MARINE MAM-MALS project, which was launched in 2016 and ended in 2019. Within this project, we developed teaching materials and tried it out on teachers and students. Now is the time for you to explore the result of these efforts. We hope that teachers as well as students will fnd the material interesting, and also that teachers will develop the material according to the needs of their students. We also hope that we can challenge the teachers' thinking about teaching, and also that we can help making students more interested in science.

Each chapter has been through extensive reviews by acknowledged experts in marine mammal biology as well as experienced teachers. We thank Jay Barlow, Annalisa Berta, Rune Dietz, Peter Evans, Jamileh Javid Pour, Sara Königson, Morgan Martin, Felix Mittermayer, Paul Nachtigall, Filipa Paiva, Joseph Schnitzler, Martin Thiel and Peter Tyack for reviewing individual chapters, and Alejandro Acevedo-Gutierrez, Niels Dohn, Carl Kinze, Kristine Pape, Ulf Saure, Volker Smit, Janto Schönberg, Ewa Wink and Bernd Würsig for providing fullbook reviews.

### **Dennis Brennecke**

Kiel, Germany

**Katrin Knickmeier**  Kiel, Germany

**Iwona Pawliczka**  Hel, Poland

**Ursula Siebert**  Büsum, Germany

**Magnus Wahlberg**  Kerteminde, Denmark

### **Contents**


### **Contributors**

**Dennis Brennecke** Kieler Forschungswerkstatt, Kiel University and Leibniz Institute for Science and Mathematics Education, Kiel, Germany

**Krishna Das** Freshwater and Oceanic Sciences Unit of Research, University of Liège, Liège, Belgium

**Katrin Knickmeier** Kieler Forschungswerkstatt, Kiel University and Leibniz Institute for Science and Mathematics Education, Kiel, Germany

**Miko**ł**aj Koss** Prof. Krzysztof Skóra Hel Marine Station, Faculty of Oceanography and Geography, University of Gdańsk, Hel, Poland Foundation for the Development of the University of Gdańsk, Gdańsk, Poland

**Katrin Kruse** Kieler Forschungswerkstatt, Kiel University and Leibniz Insti-

tute for Science and Mathematics Education, Kiel, Germany

**Anna Lorenz** Institute of Aquatic Resources, Swedish University of Agricultural Sciences, Uppsala, Sweden

**Eric Parmentier** Freshwater and Oceanic Sciences Unit of Research, University of Liège, Liège, Belgium

**Iwona Pawliczka** Prof. Krzysztof Skóra Hel Marine Station, Faculty of Oceanography and Geography, University of Gdańsk, Hel, Poland

**Anja Reckendorf** Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine Hanover, Foundation, Büsum, Germany

Institute for Parasitology, University of Veterinary Medicine Hanover, Foundation, Hannover, Germany

**Lars Seidelin** Department of Mathematics and Computer Science, LSUL— Laboratory for Coherent Educations and Learning, University of Southern Denmark, Odense, Denmark

**Ursula Siebert** Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine Hanover, Foundation, Büsum, Germany Institute for Parasitology, University of Veterinary Medicine Hanover, Foundation, Hannover, Germany

**Helen Sköld** Havets Hus, Lysekil, Sweden

**Martin Stjernstedt** Havets Hus, Lysekil, Sweden

#### X Contributors

**Bianca Unger** Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine Hanover, Foundation, Büsum, Germany

**Magnus Wahlberg** Marine Biological Research Center, University of Southern Denmark, Kerteminde, Denmark Fjord&Bælt, Margrethes Plads 1, Kerteminde, Denmark

# **Who Are the Marine Mammals?**

*Krishna Das, Helen Sköld, Anna Lorenz, and Eric Parmentier*

### **Contents**


	- 5 Get acquainted with marine mammals and how they have evolved.
	- 5 Understanding physiological and morphological adaptations to marine life.
	- 5 Learn about marine mammals found in the North Sea and Baltic Sea.

### **1 Introduction**

Marine mammals are found in several lineages among the more than 6000 species of mammals (all belonging to the class Mammalia). Not all marine mammals are closely related. Together they form a habitat-based group of animals associated with water. Mammals evolved on land some 250 million years ago. At least seven separate clades of mammals have returned independently to water, where they have adapted to aquatic habitats. Despite huge differences between species, terrestrial and marine mammals share many common features (. Table 1).

Today, some 130 living species of mammals depend on the ocean for most, or all, of their lives. Marine mammals are divided into three taxonomic orders (Cetacea, Sirenia and Carnivora) with different terrestrial ancestors (. Table 2, . Figs. 1 and 2).

Cetaceans (whales) evolved from terrestrial ancestors which were hoofed animals (ungulates, belonging to the order Artiodactyla which also contain hippopotamus, pigs and deer) more than 50 million years ago, during the geological epoch called the Eocene. The closest now-living terrestrial relative of cetaceans is the hippopotamus and the ruminants, including cattle. One of the earliest known cetaceans is *Pakicetus* (meaning 'the cetacean from Pakistan'). *Pakicetus* was mostly terrestrial but walked and most probably hunted in shallow waters. It looked like a small dog with a long snout, incisors and hooves.

Sirenians (sea cows) are herbivores that emerged during the same time period as cetaceans. Sirenians share a common ancestor with elephants and hyraxes. Early sirenians possessed an elongated body and had four legs, with dense and large ribs. They were




probably found in rivers and estuaries, living from plants and seagrass.

Pinnipeds (seals, sea lions and walruses) evolved from another group of terrestrial mammals 25 million years ago during the late Oligocene epoch. Pinnipeds shares a common ancestry with so-called *arctoid carnivores*, to which both bears and otters belong.

The polar bear (from the bear family, Ursidae) and sea and marine otters (from the family Mustelidae) are more recently derived from terrestrial clades. Polar bears evolved from brown bears around 600 thousand years ago. They have adapted to a marine and Arctic lifestyle through a lack of fur pigmentation, shorter but more curved claws, specialized front paws for swimming, and a larger and more round body. Sea and marine otters have aquatic adaptations that distinguish them from other mustelids, such as their large size.

..      **Fig. 2** Different marine mammals. Not to scale. Drawings by Annika Toth

### z **Name: Harbour porpoise (**. **Fig.** 3**)**

### *Scientifc name*: *Phocoena phocoena*

*Behaviour*: Usually a rather slow swimmer, generally wary of boats, and almost never seen to bow-ride (i.e. surf the wave created by boats, as often observed in dolphins). They can speed up and change direction quickly, sometimes making arc-shaped leaps when chasing prey. Most dives last less than 5 min. The blow is not easily seen but can be heard from quite some distance in calm weather and resembles a sharp, puffing sound. Harbour porpoises are often sighted by themselves or in small groups and prefer coastal and shallow waters, even though in some areas they are also found in deeper waters. Occasionally, they have been observed swimming up rivers.

### **2 Marine mammals from the North and Baltic Seas**

The IUCN Red List of Threatened Species is a comprehensive inventory of the global conservation status of plant and animal species. It uses a set of quantitative criteria to evaluate the extinction risk of thousands of species. These criteria are relevant to most species and all regions of the world. The IUCN Red List is an authoritative guide to the status of biological diversity.

In descending order of threat, the IUCN Red List threat categories are as follows:

Extinct Extinct in the wild Critically endangered Endangered Vulnerable Near threatened Least concern Data defcient

*Distribution*: Coastal waters of the Northern Hemisphere, both in the Atlantic and Pacifc Ocean. Also found in the Baltic and Black Seas. Probably rarer in deeper waters.

*Description*: Compared to most dolphins, the rostrum of porpoises is shorter. The dorsal side is dark grey, while the ventral side is white, and there is often a dark stripe from the corner of the mouth to the pectoral fn. The dorsal fn is low and triangular. The body shape is rather short and round, limiting heat loss in cold waters.

*Weight and size*: 35–90 kg and 135–180 cm in length. Females are larger than males.

*Lifespan*: Approximately 3–10 years, rarely up to 20 years or more.

..      **Fig. 4** Harbour seal, *Phoca vitulina*. © Prof. Krzysztof Skóra Hel Marine Station, University of Gdańsk

*Diet*: Fish (e.g., herring, gobids, sprat, cod, whiting, sole, sand eel), crustaceans and squid.

*Potential predators*: Grey seals, sharks and orcas; also killed by bottlenose dolphins.

*IUCN red list status*: North Sea and inner Danish water populations are of least concern, whereas the Baltic Sea population is critically endangered.

*Special features*: In the Baltic Sea there are two spatially separated and genetically distinct populations.

### z **Name: Harbour seal (**. **Fig.** 4**)**

### *Scientifc name*: *Phoca vitulina*

*Behaviour*: Harbour seals usually swim and dive alone, whereas on land they can congregate in great numbers. They usually stay within 50 km from where they reside on land but can also cover longer distances on feeding trips, males generally swimming larger distances than females. Harbour seals haul out on land to rest, thermoregulate, and give birth. On land, they are shy and easily disturbed by nearby boats or humans.

They are less vocal in air than grey seals but sometimes produce grunting and yelping sounds. Under water, the most commonly heard sounds are from males making repetitive stereotypical calls during the mating period in the summer. Harbour seals are curious and often play by themselves with kelp or other objects.

*Distribution*: Coastal waters in the North Atlantic and North Pacifc Oceans, and in the southwestern Baltic Sea.

*Description*: Round head, pelage in different colours and with different patches. Short, dog-shaped snout with V-shaped nostrils.

*Weight and size*: Adult males are 160– 190 cm long and weigh 70–150 kg, adult females are 150–170 cm long and weigh 60–110 kg. Size may vary between populations.

*Lifespan*: Up to 20 years, with females living longer than males.

*Diet*: Generalist feeder with a varied diet consisting of fsh, cephalopods, and crustaceans. Diet varies between populations and can be area- and season-specifc.

*Natural predators*: Orcas, sharks, walruses, grey seals and eagles (pups).

*IUCN red list status*: Least concern.

*Special features*: One of the most widely distributed species of pinnipeds. In the southern Swedish part of the Baltic Sea, there is a small and genetically distinct population.

### z **Name: Grey seal (**. **Fig.** 5**)**

*Scientifc name*: *Halichoerus grypus*

*Behaviour*: Grey seals may forage far offshore and spend the remainder of their time close to the coast. They are opportunistic feeders, consuming four to six percent of their body weight per day. Feeding methods vary between areas and populations. Small fsh are usually consumed underwater and swallowed whole. Large fsh are brought to the surface and held by prehensile front fippers. The fsh head is bitten off and discarded, while the remainder of the fsh is broken into small pieces and swallowed.

*Distribution*: East and western Atlantic, also in the Baltic Sea.

*Description*: Relatively large head with long snout, straight to convex profle and fat skull. W-shaped nostrils well separated at base. Females are silver-grey with dark patches on the dorsal side, males are dark grey with silver-grey patches; sometimes also completely brown or black.

*Weight and size*: Adult males are 200– 210 cm long and weigh 230–270 kg, adult females are 180–190 cm long and weigh 155– 186 kg. Size may vary between populations.

*Lifespan*: Up to 18 years or more (sometimes more than 40 years).

*Diet*: Generalist feeder consuming a wide range of species. Diet may be season- and area-specifc and can consist of sand eels, herring, cod, fatfshes but sometimes also birds, harbour seals and even harbour porpoises.

*Natural predators*: Sharks and orcas (and pups have been observed being eaten by older grey seals as well as by eagles).

*IUCN red list status*: Least concern.

*Special features*: A grey seal pup may gain as much as 2.5 kg per day during the time it receives milk from its mother. This is because the milk contains 50% fat.

### z **Name: Ringed seal (**. **Fig.** 6**)**

### *Scientifc name*: *Pusa hispida*

*Behaviour*: Most ringed seals do not move over large distances, and they regularly return

..      **Fig. 5** Grey seal, *Halichoerus grypus*. © Prof. Krzysztof Skóra Hel Marine Station, University of Gdańsk

to the same haul-out site during the night after their foraging trips.

*Distribution*: Circumpolar distribution throughout the Arctic, and in northern and eastern part of the Baltic Sea.

*Description*: Ring-shaped marks on their fur as adults. Small head with a short cat-like snout with V-shaped nostrils and a plump body. Their fore-fippers have strong, thick claws.

*Weight and size*: Up to 100 kg and 150 cm in length.

*Lifespan*: Up to 19 years.

*Diet*: Prey often consists of schooling species that form dense aggregations. Commonly eaten prey in the Baltic are cod, herring and amphipods. There are regional variations in diet.

*Natural predators*: Polar bears, orcas, foxes, gulls and ravens.

*IUCN red list status*: Least concern.

*Special features*: Ringed seals breed on ice. They build caves or lairs on top of the ice and under the snow by using their strong claws. Here, they give birth and nurse their young. There is a very small land-locked population of ringed seals in lake Saimaa, Finland.

### **3 Adaptation to marine life**

Living in water, marine mammals face challenges such as heat regulation, locomotion, and the need to hold their breath in search for food. As they evolved from terrestrial mammals, they have developed different adaptations to the challenges they meet with their aquatic lifestyle:


Here, we discuss adaptations to these challenges in more detail.

### **3.1 Anatomy**

Most marine mammals are large and roundish. While swimming, their drag is reduced by their torpedo-shaped bodies with short limbs and small or missing external ears. Whales, manatees and sea otters live their entire lives in water. Seals and polar bears live both on land and in water, and their bodies are therefore adapted to both environments.

Whales and dolphins have bodies adapted for moving through water. Any deviations from a torpedo shape are minimized to maintain laminar water fow around the body. Hairs, bristles, and outer ears have been lost, and sexual organs and mammary glands are placed in folds. The neck is shortened, hind limbs are suppressed and the forelimbs are fattened. Their body shape minimizes drag by allowing water to fow evenly around them.

Drag consists of several components. The most important ones are pressure and frictional drag. *Pressure drag* results from differences in water pressure between the front and rear part of the body. *Frictional drag* is the force exerted on the surface of the body due to the viscosity of the fuid. The amount of drag depends on the body shape. A sphere moving in the water develops high pressure drag (due to its large cross section area) but low frictional drag (because of the small surfaceto-volume ratio). On the other hand, a long slender body has low pressure drag (due to its small cross section) and a high frictional drag (because of the high surface-to-volume ratio). Moving effciently through water calls for minimizing both types of drag by compromising the body shape between these extremes. The shape with the smallest total drag is an elongated droplet with its largest diameter one-third body length from its front. This is the 'torpedo-like' body shape found in many dolphins and some of the fast baleen whales, such as the blue whale.

The roundish body shape, together with extraordinary thick fur or massive body fat also prevents the animal from becoming cold. Heat loss is an important issue for warmblooded animals in cold water. Newborn marine mammals rapidly gain weight and fat to prevent heat loss. The sooner the newborns can start swimming and hunting on their own, the higher are their chances to survive.

Most marine mammals have a thick layer of fat, known as blubber, below the skin. Blubber has different functions. It acts as an insulator, improving thermoregulation. It affects buoyancy and streamlines the body during hydrodynamic locomotion. Blubber stores lipids, and thus energy, that play an important role during reproduction, parturition and lactation. Many species do not feed during these activities and entirely rely on stored energy to survive. Moreover, lipid is a source of metabolic water that can be used during lactation. Their thick blubber layer causes stranded whales to overheat and dehydrate, which can often lead to death.

The senses need to be modifed when moving from air to underwater. Seeing both on land and in water can be diffcult because air and water have different light propagation properties. The *refractive index* in air is 1, in water it is 1.3. Aquatic mammals display *emmetropia* (sharp vision) while submerged, meaning their eyes are adapted for optimal focusing under water. Both pinnipeds and cetaceans have developed an almost spherical or slightly elliptical lens to provide a suffciently high refractive power under water. Fishes and cephalopods also have spherical eye lenses, so this adaptation for underwater vision has evolved independently many times, so-called *convergent evolution*. In cetaceans, emmetropia in water results in *myopia* (nearsightedness).

In seals, the lens is bifocal to accommodate well both in air and under water. Also, seals have a refective retina that makes their eyes glow at night, similar to nocturnal mammals on land (such as cats and deer). Together with a larger pupil and many rods in the retina, this makes their eyes more light-sensitive than the human eye. Light-sensitive eyes are needed when hunting at great depths and at night. In addition, the highly sensitive vibrissae of seals and the ability for echolocation in dolphins and porpoises supplements and sometimes even substitutes vision, for example, in very murky waters and at night-time.

### **3.2 Whale skeleton**

The curiously shaped skeletons of marine mammals result from evolution of the ones of ancestral mammals that lived on land.

Let us have a look at the skeleton of a harbour porpoise (. Fig. 7). The vertebral column is made up of the cervical, thoracic, lumbar, and caudal vertebrae. Cervical vertebrae are shortened and (in most species of cetaceans) fused. This helps forming the required torpedo shape but limits neck mobil-

..      **Fig. 7** Skeleton of a harbour porpoise, *Phocoena phocoena*

ity. Thoracic vertebrae are restricted to the extremely fexible rib cage, which is remarkable by its very small sternum, resulting in a higher number of 'free-foating' ribs. The thorax is extremely fexible, which allows for lungs being compressed during deep dives.

Lumbar vertebrae extend from the thorax to the anterior part of the caudal vertebrae. Hind limbs and sacrum have been lost during evolution. However, two 'free-foating' sacral bones can be found in some cetaceans. In males, they are used as attachments for muscles that can retract the penis into the genital fold.

Caudal vertebrae are easy to identify because they have *chevron bones* (bones of the ventral side of the vertebrae) that insert muscles to move the caudal fuke or hind limbs. At the caudal tip, the fuke is not supported by bones but by connective tissue. Whereas the caudal fn of most fsh is in the vertical plane, the cetacean fuke is in the horizontal plane. This is because cetaceans evolved from terrestrial mammals where fexibility for walking and running occurs in the dorso-ventral plane. Contrary to fshes, the marine mammal dorsal fn is deprived of bones. The dorsal fn works as a keel to keep equilibrium when swimming fast.

The pectoral fns (also called fippers) have evolved from forelimbs originally used to move on land. The limbs of terrestrial mammals are used to support the animal's weight and typically end with claws, nails or hooves. In cetaceans, fippers are used for manoeuvres and locomotion, as paddles. Claws, nails and hooves have disappeared. The fippers are fattened to provide greater strength during locomotion. Moreover, the fipper is shaped as a wing of an airplane and can be used to 'lift' the body upwards towards the surface.

Besides being used for locomotion, fippers, dorsal fn and fuke have a thermoregulation function. Major arteries are located centrally, surrounded by veins. This structural organization is called a *counter-current heat exchanger*: heat from the warm arterial blood fow is transferred to the surrounding veins, heating the blood returning from body extremities. This system can regulate heat in two ways. If the animal needs to cool down, the blood fow to the fn is high. If the animal needs to warm up, it can keep blood closer to the core. Moreover, vascular links between dorsal fn and fukes of dolphins and their reproductive organs allows cool blood to enter the abdominal cavity to regulate the temperature around reproductive organs.

Different modifcations can also be found in the head. An important one is the position of the nares (blowhole). In terrestrial mammals, nares are usually found rostrally (at the front) and directed horizontally or downwards. While swimming, a frontal position of nares is energetically expensive, as you need to lift your head to place your nose out of the water to take a breath. In marine mammals, nares are directed horizontally or even vertically, limiting the effort to breath. The most extreme cases are found in cetaceans, where the nose is directed straight up. Whales therefore do not need to emerge a large part of their head to breathe.

Marine mammal skulls are also characterized by elongated upper and lower jaws that result in a long mouth. Dolphins have numerous sharp conical teeth. Just as for crocodiles, their mouth 'design' is ideal for catching evasive prey, such as fast-moving fsh or squid. In porpoises, the teeth are smaller and spatelshaped. Dolphins and porpoises lack incisors, canines, premolars and molars, typically found in terrestrial mammals (and in seals), and they only have a single kind of tooth.

Baleen whales do not possess teeth, but they have rows of long baleen plates made of *keratin* (a protein also found in nails and hair), growing from their upper gums. Their upper jaw is dorsally curved whereas the lower jaw is laterally curved. Contrary to terrestrial mammals, the cartilaginous joints of the *rostral symphysis* (where the two lower jaws meet) are often missing, allowing the lateral spreading of the lower jaw. In this way they let large amounts of water enter the mouth. The water is sieved through the baleen plates on its way out. The baleen plates are broad and strong at the base but taper into fringes at the tip, forming a large brush that holds smaller prey when water is fushed through them.

### **3.3 Diving physiology**

Most humans can hold their breath for a few minutes and free-dive no deeper than 5–10 m. Marine mammals dive much deeper and for longer durations. For example, Weddell seals can dive deeper than 700 m and stay below the surface for more than an hour. How is this possible?

Diving marine mammals undergo a *dive response*. The heart rate drops tremendously at the start of the dive. In grey seals, it can drop from 120 to 5 beats per minute. Also, blood supply is funnelled to the most vital organs of the animal, such as the brain and heart, whereas most other organs receive little blood and oxygen. The blood volume per kilogram body weight of marine mammals is almost twice as large compared to humans. Both blood and muscles of marine mammals contain larger amounts of oxygen-binding molecules, called haemoglobin (in blood) and myoglobin (in muscles). Whale and seal muscles are deeply red, almost black, because of their high content of myoglobin.

The dive response and other adaptations help marine mammals to store oxygen during their remarkably long and deep dives. Interestingly, humans also have a dive response with a reduced heartbeat, but it is not as dramatic as for marine mammals. While humans as well as cetaceans usually take a big breath before diving, seals breathe out and empty their lungs before they dive. An advantage with emptying the lungs is to prevent gases in the lungs becoming dissolved in blood and tissues at greater depths. If the animal surfaces too quickly, dissolved gases may result in bubbles that can cause blood clots. This problem is called *decompression sickness* and can be reduced if the lungs are emptied before diving. Empty lungs also allow the animal to sink passively without actively swimming upon decent. Many marine mammals can tolerate their lungs collapsing during deep dives through the adaptations of the rib cages explained above.

### **Current topics of marine mammal research**

The dive refex aids in the conservation of oxygen stores in mammals by initiating several specifc physiologic changes during immersion. The dive response was frst described in the 1940s. In these trials, the animal was forced under the surface and its physiological response was recorded. Nowadays, the diving response is investigated in trained as well as wild animals of many different species.

In 2015, Dr Siri Elmegaard and her research team from Aarhus University studied trained harbour porpoises at Fjord&Bælt in Kerteminde, Denmark. Siri tested if a porpoise could voluntarily adjust its diving response depending on the duration of the dive. They designed an experiment where the animal was trained to go for a short or a long dive. The length of the dive was indicated to the animal before the trial using an acoustic signal. During the trials, the animal's heart rate was measured using a device attached by suction cups to the animal (. Fig. 8).

The experiment indicated that harbour porpoises may be able to adjust their heartbeat voluntarily depending on the length of the dive. In this way, the animal can optimize the oxygen demands while diving. If this phenomenon is widely spread in different species, it may have important implications for conservation biology of cetaceans. If the animal is disturbed and forced to dive, for example being scared by a boat, the ability to save energy during the dive may be negatively affected if there is no time for the animal to 'plan' its dive. Therefore, its ability to hunt for prey may be reduced.

### **4 Teaching materials**

### ?**Exercise 1.1: Marine mammals vs. terrestrial ancestors**

Marine mammals are divided into three taxonomic group (orders Cetacea, Sirenia and Carnivora), each with its own terrestrial ancestor. Through evolution, these groups gradually adapted to the marine environment.

Select a marine mammal and compare it with related animals that live on land (. Fig. 1). What is the body shape like? How long are tail and limbs? What do the ears look like? (. Fig. 2)? Where are the nares?

### ?**Exercise 1.2: IUCN red list of threatened species**

Many species of marine mammals are found on the *IUCN Red List of Threatened Species* (7 https://www.iucnredlist.org/). The IUCN Red List is an authoritative guide to the status of biological diversity. The list uses a set of quantitative criteria to evaluate the extinction risk of animals from all regions of the world. There are different threat categories: 'Extinct', 'Critically Endangered', 'Endangered' and 'Vulnerable' consider species threatened by global extinction. 'Near Threatened' concerns species close to being threatened, or species that would be threatened without ongoing conservation measures. Species of 'Least Concern' have a low risk of extinction, and 'Data Defcient' means there is no assessment because of insuffcient data.

Which marine mammals have you encountered, or would you like to encoun-

..      **Fig. 8** Measuring the dive response in a harbour porpoise using a device attached to the back of the animal. © Siri Elmegaard, Aarhus University and Fjord&Bælt

ter? Find out what their status is on the IUCN Red List.

### ?**Exercise 1.3: Mammalian diving refex: How is our heart rate afected by diving?**

Marine mammals must come up to the surface to breathe. When they dive, they need to stay underwater for a long time to enable foraging. Marine mammals rely on anatomical features and physiological responses that have evolved to increase oxygen storage in the body as well as to reduce the use of oxygen for non-essential activities during dives. Marine mammals are also able to funnel their blood fow to essential organs, such as the brain, by constricting some of their blood vessels (*peripheral vasoconstriction*). They also conserve energy and reduce oxygen consumption by lowering their heart rate.

In this exercise, we will see what happens to *your* heart rate when *you* submerge your face in cold water.

Before you do the experiment, think about what you expect will happen. Do you think your heart rate will increase, stay the same or decrease while you are submerged?

### z **Required materials**


### z **Tasks**


You can extend this exercise: Measure heart rates from all students in the class and calculate average change in heart rate. Is there a difference in diving response between males and females, or swimmers and non-swimmers? Induce the diving response by using a bag of ice on different body parts (back of neck, wrists, nose and eyes). What is the effect of such actions on the diving response? Repeat measurements with water of different temperatures. What temperature induce the strongest dive response?

### z **Results**

When mammals dive, their heart rate decreases—this is called the mammalian diving response. Decreased heart rate conserve energy expenditure and oxygen consumption. As a result, mammals can stay underwater longer and therefore also dive deeper. The diving refex is stronger in marine than terrestrial mammals to allow for long dives. Elephant seals have a very strong dive response, and they can stay underwater for more than an hour. They are also helped by a high myoglobin content and a large blood volume (. Table 3).

### ?**Exercise 1.4: Thermoregulation and insulation. How does cold water afect your muscles?**

Heat is lost 20 times faster in water than in air. When marine mammals dive, they need to stay warm and avoid losing too much heat. One of the ways they do this is having a thick layer of insulation called blubber, or a fur covering their body. Cetaceans only have blubber and sea otters only have fur, whereas seals have both. Blubber and fur decrease heat loss. Bowhead whales, for example, have a blubber thickness of up to 50 cm, serving them well in Arctic waters. Sea otters have the densest fur of any mammal. A mere 1 cm2 of their fur amounts to the entire number of hairs that humans have on their head.

In this exercise, we will investigate how cold water affects our muscles.

What do you think will happen to your muscle strength when you put your hand in cold water?

Do you think your strength will be affected? Will you get stronger or weaker?

..      **Table 3** (7 Exercise 1.3) Results: Dive response. *bpm* beats per minute. Complete the table and the graph below



### z **Required materials**


### z **Tasks**

1. Measure water temperature of the water.


dynamometer as hard as you can. Record your strength in . Table 4.

If you want to, you can extend this exercise. Collect results from all students and make a graph to see if there is a difference between males and females in the effect of low temperatures. The experiment can also be repeated using different temperatures of water. Is there a difference in muscle strength between submersion in 10 °C compared to 4 °C? Make a graph to explore the relationship between muscle strength and temperature. Instead of a thick cotton glove, use a large plastic glove and fll it with butter to simulate blubber. Use different amounts of butter to compare insulation effciency. To make this exercise less messy and to use less butter, students can put on skin-tight plastic gloves on their hand before putting their hand in the large glove flled with butter. You can then use the same buttered glove for all students.

### z **Results**

Thermoregulation is when an organism can keep its body warm even if its surroundings are colder. Insulation prevents the loss of body heat. When marine mammals dive into cold water, they need to keep their bodies warm. One way they do this is by having blubber and/or fur. This helps insulate the body and allows the animal to stay in the water without getting hypothermia (. Table 4).

### z **Home Pages**

Committee on Taxonomy, Society for Marine Mammalogy; List of marine mammal species and subspecies: 7www.marinemammalscience. org

IUCN Red List: 7 https://www.iucnredlist. org

### **Suggested reading**


**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

### **Marine Mammal Acoustics**

*Anja Reckendorf, Lars Seidelin, and Magnus Wahlberg*

### **Contents**


**Supplementary Information** The online version contains supplementary material available at [https://doi.org/10.1007/978-3-031-06836-2\_2].

### n**Learning goals**


### **1 Introduction**

We live in a world of sounds: both natural and human-made (anthropogenic) ones. So do the animals with which we share this planet. Many of them depend on their abilities to navigate the *soundscape* to survive. Marine mammals use sound both for sensing their surroundings and to communicate, sometimes over long distances. Knowledge of bioacoustics and the physics of sound are important, both when trying to understand the lives of marine mammals and also when trying to protect them from human disturbances.

The underwater world contains many different sounds, which can have natural causes like thunder, winds, animal sounds and rain, or be man-made. Marine mammals are well adapted to natural sounds; they react appropriately to sounds of interest to them. 'Noise pollution' is the sum of all additional, unnatural sounds which disturb animals. Sounds are not heard equally well by all animals. An acoustic signal which is important to one species may be without interest or disturbing to another. It is diffcult to assess the impact of noise on animals, as we often need to address the effects on different species separately.

### **2 The physics of sound**

Sounds are waves, somewhat similar to ocean waves you can see rolling in on a beach or that you create yourself in your bathtub. Sound waves can be generated by, for example, a vibrating membrane. Particles of the surrounding medium are set in motion by the membrane and move from side to side, condensing and relaxing the medium. Sound wave propagation is therefore dependent on the oscillation of matter surrounding the sound source. Accordingly, sound needs a medium to propagate. The medium can be a gas (such as air), liquid (such as water) or a solid (such as the seafoor). In outer space, where there is no medium, sound cannot propagate.

The particles in the medium do not actually travel with the sound wave. They oscillate and end up in the same location where they started after the wave has passed. For an animated graphic of sound propagation click 7 here and 7 here.

A sound wave is a *longitudinal* wave. The medium's particles move back and forth parallel to the direction in which the sound wave travels. In contrast, in a *transverse wave* (such as an electromagnetic wave), the particles or feld move perpendicular to the direction in which the wave is travelling. Water waves are more complicated: here, the particles move in a circular fashion.

Check online supplementary animated graphic . Fig. S1.

The easiest described sounds are 'pure tones', or sinusoidal waves. They can also be called signal 'atoms', as any kind of sound can be constructed out of sinusoidal waves. Sinusoidal waves are defned by their amplitude, frequency and phase (. Fig. 1).

**Amplitude**

A*mplitude* measures the local pressure fuctuation created by the movement of the particles, measured in pascals (Pa; or newton/m2, N/m2; . Fig. 1). One pascal equals the pressure generated by 1 newton over an area of 1 m2. In air, one pascal is a very high sound level, similar to noise generated by cars on a highway at a close distance. Compared to the atmospheric pressure, which is around 100 kPa at the surface of the Earth, the pressure fuctuations generated by most sounds are small.

..      **Fig. 1** Left top: A sound wave, depicted as a function of time (recorded at a certain position). Left bottom: The same sound wave, depicted as a function of range (recorded at several locations). Right top and bot-

### **Frequency**

*Frequency* is defned by the number of wave cycles in 1 s, measured in hertz (Hz). Thus, 1 Hz is one cycle/sec, while a kilohertz (kHz) is one thousand cycles per second.

The frequency is closely related to the wave's *pitch*, which is the animal's perception of how 'high' (*treble*) or 'low' (*bass*) the sound is. Decreasing the frequency lowers the sound's pitch and makes it more 'basslike', while increasing the frequency raises it (making the sound more 'treble-like'; . Fig. 1). Different species of animals have their best hearing at different frequencies: humans hear best at 2–4 kHz, while porpoises hear best at 100–140 kHz.

### **Intensity**

Another useful unit is the *intensity* of the wave, which is defned as *I* = *p*2/(*ρc*), where *p* is the sound pressure (measured in Pa), *ρ* is the density of the medium (in kg/m3) and *c* is the speed of sound in the specifc medium (in m/s). Intensity is measured in units of W/m2 (watts/metre2). Intensity is related, but not identical to, how loud humans and other animals perceive sound (for humans, the latter is called the *loudness* of the sound).

tom: a sound wave of higher frequency, depicted as a function of time and range. A sinusoidal sound wave is characterized by its 'height' (amplitude), frequency and phase (determining at which time the peak occurs)

It is important to understand the basics of pressure and intensity before we move on to discuss how well animals hear. When comparing hearing in air and underwater, it makes a difference if we report hearing thresholds (i.e. the weakest sound an animal can here) in pressure or intensity units. As we will see below, when measured in units of pascals, underwater hearing thresholds seem higher than aerial ones. However, this does not necessarily mean that marine mammals hear worse underwater than terrestrial mammals hear in air. The difference is to a large part a matter of the composition of the medium in which the sound propagates. Because water is denser than air, a pascal of sound underwater carries less intensity than a pascal of sound in air. Thus, comparing in-air and underwater sound levels is by no means trivial. When reporting thresholds in units of intensity, some marine mammals (such as seals, which live a semi-aquatic lifestyle) have similar hearing thresholds in air and underwater, while others (such as dolphins, which are entirely aquatic) have poorer hearing in air but extremely sensitive hearing underwater.

### **Sound levels expressed as decibels**

Because the span in sound pressures that can be observed in nature is huge, the sound amplitude scale is often compressed into a logarithmic scale, known as *the decibel scale*. Decibels are calculated as

### dB = 20 ( ), <sup>10</sup> <sup>0</sup> log / *p p*

where log10 is the base-10 logarithm, p is the measured pressure (in Pa), and *p*<sup>0</sup> is the so-called *reference pressure*, which is *p*0 = 20 μPa (micropascals) for airborne sounds, and *p*<sup>0</sup> = 1 μPa for underwater sound. The reference pressure in air is close to the human hearing threshold at 1 kHz. In this way, the hearing threshold of humans at this frequency is 0 dB re 20 μPa (try to calculate this yourself). The underwater reference pressure does not have any biological meaning but has been hand-picked by a scientifc committee. To indicate which reference pressure is used, in-air sound pressure levels are reported as dB re 20 μPa and underwater as dB re 1 μPa (. Fig. 2).

Because of the differences in reference units as well as in speed of sound and density of air and water, it is not easy to compare in-air decibel levels with underwater ones. A sound signal of equal pressure in both media is 26 dB higher in water than in air (due to the different reference pressures), and a sound of equal intensity is 62 dB higher in water than in air (due to different reference pressures and impedances).

Let's compare the decibel scales in air and underwater (. Fig. 2). In air, the scale of audible sounds spans from the hearing threshold, which for most mammals is lower than 20 μPa up to about 100 Pa, around the *threshold of pain*. This means a difference of 6–7 orders of magnitude between the lowest and highest point of the audible scale. In decibel units, the biologically relevant in-air scale is from a bit less than 0 dB to more than 130 dB re 20 μPa. In water, the lowest hearing thresholds of marine mammals are about 100–1000 μPa (which in decibels become 40–60 dB re 1 μPa), while the threshold of pain is probably beyond 1 or 10 kPa (180–200 dB re 1 μPa). The loudest sounds that can be produced in air, such as sounds from rife shots and jet engines, can be up to around 180 dB re 20 μPa. Beyond this sound level, the air molecules cannot maintain the extremely large particle motions and start to behave in ways not easily described by physics. Underwater, the loudest animal sounds are produced by sperm whales, which sometimes click at about 240 dB re 1 μPa, if recorded at a distance of 1 m. Even louder sounds exist, but these are mainly of human origin, such as the sounds from sonars and underwater explosions. Remember though that to directly compare the sound intensity in air and underwater, you have to subtract 62 dB from the underwater decibels.

Another important feature of a sound wave is its frequency content. Young humans can hear from about 20 Hz up to 20 kHz. With age, the upper hearing limit is rapidly decreasing so most people older than 50 years have a hard time hearing sounds above 10 kHz. Humans hear best at 2–4 kHz, which is signifcantly higher than the frequencies where we emphasise our speech, at a few 100s of hertz (. Fig. 3).

#### ► **Example**

Human hearing is not fne-tuned to the frequencies at which we communicate. But why do we speak at different frequencies than our best hearing occurs? A crowded bus ride may give you a hint. You can easily continue talking to your friend nearby, in spite of all the noise of other people talking around you. If a baby starts crying however—and babies cry in the 2–4 kHz range where humans hear best—you may stop your conversation to see if any help is needed or soon consider switching to another bus to continue your conversation. Our hearing seems to be evolutionary tuned to listen in for infants that need to be comforted. ◄

The speed at which a sound wave travels is different for every medium. It depends on the density, temperature and a few other parameters, like ambient pressure and (for underwater

..      **Fig. 2** In-air and underwater decibel scales. The reference pressure for airborne sounds is dB re 20 μPa, while dB re 1 μPa is the reference pressure for underwa-

sound) salinity. In air, the speed of sound is 330–340 m/s, and in water 1450–1500 m/s. Thus, sound travels about 4.4 times faster underwater than in air.

The different acoustic properties of air and water have implications for the way we perceive sound in the two media. For example, an important cue when listening for sounds is to determine their direction. Many animals,

ter sounds. The water dB scale is shifted by 62 dB, so that in-air and underwater sounds at the same vertical location have the same acoustic intensity

and humans, do this primarily by gauging the difference in timing or intensity of the sound received at each ear. Both timing and intensity differences will become smaller in water. Due to the high speed of sound transmission underwater, sound is received at both ears closer in time than for airborne sounds. Furthermore, for a signal with a certain frequency content, the wavelength is longer

..      **Fig. 3** Left: the human hearing threshold in blue, and threshold of pain shown in red. On the right, the audiogram of a harbour porpoise (green) is compared to a human audiogram (blue). The audiogram thresh-

underwater than in air, as the wavelength is the ratio between speed of sound and frequency. Due to the longer wavelengths, and the similarity of fesh, bone and water density, the animal's head is less effcient in shielding signals underwater than in air. Therefore, intensity difference cues between the two ears to determine the direction of a sound source become less effcient in water. Terrestrially adapted animals, and humans, have a very hard time determining the direction of a sound source underwater. Marine mammals, however, have certain anatomical and physiological adaptations to tease out the direction of underwater sounds. Porpoises, for example, have acoustically decoupled inner ears: they are detached from the skull and surrounded by air compartments.

### **3 Hearing and sound production**

Marine mammals use sound to communicate over short and long distances, to acoustically sense their surroundings and navigate underwater, locate prey and mating partners, and to avoid predators.

Depending on the species, the upper hearing limit differs tremendously. Seals can hear well up to about 20 kHz in air, whereas their underwater frequency range is more than doubled, up to 50 kHz. Their hearing is adapted to life both in air and water. Toothed whales hear well underwater but poorly in air.

olds have been shifted so that the intensity level is the same for the underwater and in-air hearing thresholds. Left fgure from Larsen and Wahlberg (2017), right fgure from Wahlberg et al. (2015)

Many of them can hear even higher frequencies than seals. The record holder are small odontocetes such as the harbour porpoise, which can hear frequencies higher than 140 kHz. Porpoises hear best in the frequency range where they produce their echolocation signals (. Fig. 4). Their hearing sensitivity at these frequencies is among the best sensitivities found in any aquatic mammal.

Marine mammals produce a large repertoire of different sounds. In most cases you can quite easily detect the difference between sounds from a seal, a dolphin and a baleen whale. Seals produce sounds both in air and underwater in the same frequency range as humans, mainly for communication and during mating activities. Dolphins produce clicks, burst-pulsed sounds and whistles. Some of these signals are produced in the frequency range audible to humans, but they often also contain higher, so-called *ultrasonic*, frequencies. Baleen whales produce extremely lowfrequency sounds. Blue and fn whales regularly sing below 20 Hz, which is the lower frequency limit of human hearing; sounds below this limit are called *infrasound*.

Sound is one of the most useful ways of communication, above and especially underwater. Many marine animals have good eyesight, but even in the clearest tropical waters, visibility is restricted to a few tens of metres. Sound on the other hand travels much further. Many low-frequency sounds may be often heard over very large distances. Many

..      **Fig. 4** Hearing (in black) and sound production (in grey) ranges in a selection of animals

marine organisms have developed ways to produce and detect sound. Whales, for instance, have developed distinct communication strategies and orientation systems, which allow them to fnd prey and communicate with conspecifcs over great distances. For example, blue whale calls have been heard at ranges of tens or even hundreds of kilometres.

Toothed whales (odontocetes) use echolocation. They produce very high-frequency sound waves by forcing air past so-called *phonic lips* into the air sacs of their nasal passages. The clicks are transmitted through sound conducting acoustic fat of different densities in the front of their head (the *melon*), directing the sound in to a narrow beam. The emitted sound waves travel through the water until they reach an object, such as a prey item or an underwater obstacle. The object refects some of the sound energy, creating an echo. The returning echoes are mainly received through the whale's lower jaw, containing fat which channels the perceived sound towards their inner ear complex (Fig. 5). Thus, by emitting ultrasonic sound pulses, odontocetes listen for echoes and can detect objects underwater. They can basically 'see' their environment through the sound waves they produce, in some ways similar to the echo sounder on board a ship.

..      **Fig. 5** Sound production and reception in a harbour porpoise. The purple structure in the forehead is the acoustic fat of the melon, which channels the emitted clicks (green). The sound is refected by the fsh (orange

Baleen whales and seals do not use echolocation, but they still rely on sound and hearing for survival. Seals, and probably also baleen whales, produce sounds with their larynx and some additional air sacs, similar to terrestrial mammals. Besides good underwater and in-air hearing abilities, pinnipeds (true seals, walrus and eared seals) can perceive water disturbances with their whiskers to detect water movements generated by swimming fsh.

### ► **Example**

Marine mammals have evolved adaptations that allow them to use sounds both to detect prey and to avoid predators. An interesting example is the frequency range of sounds and hearing of harbour porpoises compared to one of their predators, orcas. Orca sounds consist of a wide range of whistles and pulsed calls, with fundamental frequencies as low as a few kHz and harmonics beyond 100 kHz. Their best hearing is around 40 kHz. Harbour porpoises hear best between 120 and 140 kHz but can also hear sounds as low as a few kHz. Harbour porpoise signals, on the

dashed line) and mainly received through the lower jaw. The red shading indicates the mandibular acoustic fat close to the ear bone. © Annika Toth

other hand, do not contain much energy at frequencies below 100 kHz and are centred around 120–140 kHz, where they hear best. It is believed that porpoises have adapted their sound production to higher frequencies, which are out of the hearing range of orcas. This prevents orcas from hearing sounds from their potential prey. Porpoises, on the other hand, can hear the sounds from nearby orcas and may therefore be able to avoid being captured. However, orcas have highly specialised hunting strategies and often stop making sounds before starting a hunt, making it more diffcult for their prey to evade the attack.

Some of the strongest reactions to sounds played to marine mammals occur when a playback signal sounds like a natural predator. Again, orcas are an interesting example. There are different types of orcas: some feed on marine mammals, while others only eat fsh. The different orca types also have different sound repertoires. Orca sounds were played back to Canadian harbour seals, which are regularly preyed upon by orcas. The seals responded aversively to sounds from mammal-eating orcas, but they did not respond to calls of fsh-eating orcas. ◄

There are many ways humans utilise the oceans, and many of these activities introduce sound into the natural environment. Underwater noise pollution is caused by, for example, recreational boats, commercial shipping, windfarms, oil rigs, underwater exploration for oil and gas, and military activities. Highly utilised areas often have particularly high levels of underwater sound. Noise pollution may however be just as bad or even worse in quieter areas due to a smaller degree of *habituation* (become accustomed to a behaviour or condition) in animals living in such environments.

Because many marine mammals use acoustics as an important way to detect prey, to communicate or to orient themselves, a functional hearing system is of uttermost importance to them. To a certain degree, marine animals can increase the sound level or frequency range of their communication signals to make them more audible under noisy conditions. If communication sounds are masked by anthropogenic noise, they may not be able to hear calls of conspecifcs to fnd mating opportunities or food. This can potentially play a major role in individual or species survival.

Noise can also disturb the animals' natural behaviour, make them leave their known habitat to fnd more silent locations, interrupt feeding, change diving behaviour, maybe even cause reproductive impairment through acute and chronic stress, and lead to temporal or permanent changes in distribution. Loud continuous or impulsive noise can damage hearing at certain frequencies, temporarily or permanently, which can result in failure to hear important signals, such as an approaching ship or a certain frequency component of mating calls. Additionally, certain types of anthropogenic noise, like military sonar, can lead to death when deep-diving whales attempt to escape or evade the sound by ascending too quickly.

Hearing impairment is caused by exposure to loud sounds, also to less intense but continuous noise over longer periods. If temporary hearing impairment occurs, it is called temporary threshold shift (TTS). A TTS is a passing increase in the auditory threshold resulting in momentary hearing impairment. We humans know this phenomenon as the 'discotheque effect', as our hearing is temporarily reduced after exposure to loud music. A permanent hearing threshold shift can occur as a result of repeated TTS events or from a single exposure to an intense sound. Both humans and marine mammals can become permanently less sensitive or even deaf to sounds of certain frequencies after loud or long exposure of sound.

### ► **Example**

Another problem that can be investigated with bioacoustics is collisions between ships and whales. The *International Whaling Commission* runs a global ship strike database (7 http://iwc. int/ship-strikes), and it shows an increasing number of records over the last years. Why do whales and manatees get hit by vessels instead of avoiding them?

One of the reasons may be that the main noise source of a boat is the engine, which is situated in the stern of the boat. The hull is shielding the engine noise towards the front, so straight ahead of the boat the noise level is substantially reduced. If the animal approaches the boat sideways, the noise level drastically increases, making it aware of the approaching danger. If an animal forages or sleeps straight ahead in the ship's pathway, it may not perceive the sound of the engine and propellers, making it more vulnerable to collide with the ship, while whales startled by noise tend to surface rapidly, putting themselves in greater danger for collisions at the surface. The animal may even seek out a location straight ahead of the boat, to avoid too much noise from the approaching vessel. Additionally, underestimation of vessel speed, and maybe also hearing impairment, could also explain why animals are increasingly colliding with boats. Also, the number of fast-moving boats in waters frequented by cetaceans and manatees are constantly increasing. ◄

Continuous stress through noise pollution can supress the immune system and make marine life more vulnerable to infectious diseases and parasitic infections. Many marine mammals hear and communicate at frequencies different from the ones used by humans. They may therefore be affected by sounds that we cannot hear. Thus, when evaluating noise effects on marine mammals, it is important to use broadband recordings and analysis systems that can detect sounds also outside the hearing range of humans.

We need more research on the current levels of noise in the oceans, and how noise affect marine fauna. Politicians and decision makers need to take the results from such research into account when judging if mitigation measures are needed. The environmental impact assessment of new marine activities should include potential effects of noise emission. When needed, successfully tested sound mitigation measures should be implemented. Such measures could include effective animal warning devices used prior to military sonar, or so-called 'bubble curtains' used during construction work (see Exercise 5). One could also envision the development of quieter ship engines, changing shipping routes and harbour entry lanes, or speed reduction zones.

### **Tip**

Buying more local goods instead of having everything shipped from abroad is another way to improve the current situation of extensive shipping (if you want to learn more about the marine traffc density in your area, you can search on the internet for links displaying marine traffc in your country's coastal zones or exclusive economic zone). Thus, by adjusting our personal behaviour we may improve the situation not only for marine mammals but also for the marine environment in general.

**Current topics of acoustic and noise pollution research on marine mammals**

How can we use acoustic research to protect marine mammals and to learn more about them?

We still do not know much about how marine mammals communicate and orientate themselves underwater with sound. Researchers work with trained animals, sometimes blindfolded to ascertain they only make use of auditory cues during the experiments. In this way, it can be shown that, for example, blindfolded toothed whales are able to fnd their way through a maze or detect and catch prey. This is considered the classical evidence of their ability to echolocate.

We can also investigate the hearing abilities of trained animals by hearing tests. This can be done in the same way as with humans: When a sound is played during an experiment, the animal is trained to indicate if it heard the sound by putting its snout on a certain *response symbol*. The hearing abilities of stranded individuals can be checked through measurements of their *auditory brainstem response* (ABR), small electrical potentials originating from the brain in response to auditory stimuli. The electrical potentials are recorded from the skin of the animal with electrodes embedded in suction cups, which are attached to the head. In this way we can measure if animals can hear a certain sound without being trained for a hearing test. The same methodology is used to detect hearing problems in newborn human babies. In stranded marine mammals, ABR measurements are sometimes used as a health parameter: The animal needs to be able to hear the species-specifc frequencies to be released back into the wild.

Another approach to study the impact of noise pollution on marine mammals is using acoustic data loggers that can be deployed in critical habitats or along shipping channels. The data loggers record calls of the target species and ambient noise. In this way, scientists can better understand species distribution and habitat use without having to be continuously present on a boat for observations. Real-time passive acoustic sensors can transmit the sounds of seals and whales via satellite or radio links to a unit, which informs captains that animals are present, and that caution has to be practiced once an alert has been sent.

If you want to learn more, *Discovery of Sound in the Sea* offers great further learning materials and updated information on their web page 7 https://dosits.org/ (only in English).

### **5 Teaching materials**

### ?**Exercise 2.1: The frequencer**

Have you ever wondered why some people hear sounds that others cannot hear? What are the frequency limits of your hearing, and are both of your ears equally sensitive to sound?

By listening to sounds of different frequency and intensity, you can register the frequency limits of your hearing. You can then compare your hearing limits with the ones of other animals (such as marine mammals; see an example in . Fig. 3) to better understand in what ways our hearing differs from theirs.

### z **Required materials**


### z **Tasks**


### z **Results**

The result will be your own, personal frequency limits of your hearing.

Compare your results to other students and repeat the experiment with people of different age classes, like your parents and grandparents. Can you see differences in the hearing limits?

The results will not be as accurate as an audiogram measured by professional audiologists, as the played back sound level will depend on the type of loudspeaker.

### ?**Exercise 2.2: Human echolocation**

Imagine you are trapped in a dark room you are unfamiliar with. How could you orientate yourself? Do you think you could teach yourself *human echolocation*?

Not only bats and toothed whales use echolocation—humans can also learn to echolocate, and some can become quite good at it. Visually impaired humans sometimes spontaneously learn to echolocate to compensate for their lack of vision. This phenomenon was formerly called 'facial vision' but is now known to be echolocation. Interestingly, one of the best human echolocators known, Daniel Kish from California, remembers learning this skill while being only a few years old. He only understood that he was using a method comparable to bats and dolphins when 20 years old. If you want to know more about this technique, check out 7 https://visioneers.org/.


### z **Tasks**


### z **Results**

When approaching a wall, the blindfolded student will notice a change in the returning echo of the emitted click sound. This should cause the student to stop or to turn, instead of walking into the wall. When stopped in front of a wall, the student should slowly reach out for them to appreciate the actual distance. You can also leave an opening in the shielded circle, that has to be found by echolocation. Afterwards, the students can disperse in the room and the blindfolded one can try to locate them by echolocation and fnd a way to navigate around them. Additionally, if the students are trained to echolocate, different materials can be tested, since harder surfaces (e.g. a white board) refect sound in a different way than softer ones (e.g. cardboard) do.

### ?**Exercise 2.3: Name the sound**

How much do you know about animal, environmental and anthropogenic sounds? And how much do you know about underwater sounds? Do you think you can discern natural from man-made underwater sounds

..      **Fig. 6** Human echolocation (7 Exercise 2.2). The students stand in a circle, shielding themselves with panel 'walls', while a blindfolded student is standing

inside the circle. The blindfolded emits click sounds while slowly walking around, trying to fgure out where the 'walls' are by listening for returning echoes

easily? You have surely listened to songbirds, and you may have tried to identify them by their song. There are many more natural sounds to explore. In this exercise, we focus on some underwater sound examples that are completely unknown to most people. Can you guess the origin of those sounds?

### z **Required materials**


### z **Tasks**

1: Listen to the automatically played sound and repeat it by clicking on the small speaker symbol.

Guess its origin before continuing to reveal the four provided possible answers.

Was your frst guess represented in the four answer options?

If not, choose A, B, C or D as your answer. If so, was your answer correct?

### z **Results**

You will see how easy or diffcult it is to discern natural and man-made sounds from each other. Probably animals often have the same diffculties as we do.

### ?**Exercise 2.4: Build your own hydrophone**

Do you think that there is a simple technological way for us to hear sounds inside natural bodies of water? If so, what do you think you will hear down there?

Hydrophones are underwater microphones that can be easily built from a few components. With a hydrophone, you can listen for animals, such as whales and seals communicating with one another, or just the general underwater soundscape, sounding so eerie and unfamiliar to most of us 'land dwellers'. And with the right materials, it only takes 30 min to build your own hydrophone.

### z **Required materials (**. **Fig.** 7a**)**

5 This exercise includes soldering, so proper safety precautions need to be in place and care is advised. A fume hood or other ventilation system is needed, students have to be extra cautious while the soldering iron is connected and accordingly need supervision for the soldering part of the task. If soldering is considered too dangerous or unfeasible during a class exercise, this part can also be prepared prior to the experiment.


### z **Tasks**


..      **Fig. 7** Build your own hydrophone (7 Exercise 2.4). **a** All necessary materials laid out on the working desk. **b**

sound-sensitive crystal. Always take caution not to inhale solder fumes (. Fig. 7b).

3. Attach the amplifer to the connector, connect the output of the amplifer to the loudspeaker or headphones and switch it on. Now perform a 'tap test': tap gently on the crystal—you should hear a sharp noise through the loudspeaker.

Soldering the cable, one strand on each side of the piezoelectric crystal. **c** After placing the crystal in the oil flled container, everything is connected and tested


### z **Results**

The vegetable oil does not conduct electricity, but it conducts sound waves: therefore, the underwater sound waves can reach the piezoelectric crystal. The crystal transforms the pressure into voltage. The voltage is picked up by the cable strands and gets amplifed before being transmitted to the loudspeaker. Thus, sound can be transmitted to the speaker without short-circuiting the crystal.

#### **Tip**

Bring the hydrophone out to a dock by a lake or by the sea and sink it into the water. Take caution to keep the rest of the electronics dry. Now, listen to the sounds. You can also splash the water surface with your fngers or throw a small stone into the water. You can hear if you can detect fsh or other natural sounds, or perhaps you can hear a passing boat?

### ?**Exercise 2.5: Build a bubble curtain**

Imagine you want to build an offshore wind farm, to generate renewable, clean energy. How would that effect aquatic life in the area? What can be done to protect them from harmful noise impacts?

Bubble curtains are noise mitigation measures that are used to dampen and absorb sounds of underwater constructions to prevent extensive hearing loss and noise harassment of marine mammals close to the construction location. Sometimes, huge bubble curtain systems are built around construction sites and activated when necessary. If you are interested in more information and pictures regarding this topic, search the internet for, for example, *The Big Bubble Curtain* by BBC.

In this experiment, we will build a miniature bubble curtain to show the effectiveness of such a mitigation device.

### z **Required materials**

5 Air compressor (it can be a very simple, cheap aquarium pump, but the stronger the compressor, the better the result).


### z **Tasks**


The students should be silent during the entire experiment.


..      **Fig. 8** Build a bubble curtain (7 Exercise 2.5). **a** Air bubble tube for aquaria, the air holes are clearly visible. The end needs to be sealed; here we use glue. **b** Complete bubble curtain setup with aquarium pump, connective

hose and air bubble tube. **c** Running bubble curtain experiment. The red alarm functions as free-foating underwater sound source. The white, self-built hydrophone is used to measure sound levels inside and outside the curtain for comparison

6. Think about the implementation of a bubble curtain on a large scale. Which materials are needed to make it work? Are there other problems that could be caused by using a bubble curtain?

### z **Results**

When the bubble curtain appears, there should be a clearly detectable drop in the sound level. Due to the limited amount of air holes in the commercially available tubes or depending on the strength of the used compressor, the effectiveness of this experiment is often not huge, but the students can get a good feeling for how effective it can be if more air bubbles and dual or triple layers are used.

For Task 6, additional ship traffc around the construction site, electricity supply to the construction site and running of loud generators should be considered, as well as huge hoses on the sea foor, likely damaging plants and microhabitats. Still, the impact of piledriving is usually considered more dangerous and needs mitigation measures, even if they come at additional environmental costs.

### **Tip**

By submerging the active sound device in the water, you can try to explain a hard sound barrier and sound reflection. The density difference between the two media (air and water) is several hundredfold; therefore, the two media form a *boundary* and we cannot hear what is happening underwater while we listen in air. This is why bodies of water usually appear silent to us. In this case, we still hear the sound of the panic alarm, because it is loud and the container walls transmit the sound back into the air. To prove this, let the alarm sink to the bottom, and the transmission of the sound will appear louder. Try the bubble curtain again with the sound device lying on the bottom. It will not work well, due to sound being transmitted by the container walls. You can also use a stethoscope to listen to the sound from inside the aquarium and better avoid the effects of the walls.

If the device would be submerged in the ocean where the sound is not redirected and transmitted, we would not hear it at the water surface. If we are submerged, we can hear more of the sounds present underwater. However, the airwater sound barrier still exists inside our ears, so we do not hear underwater sounds as good as in-air sounds. Many underwater sounds are outside the human hearing range but within the hearing range of marine life. Often, we may not think enough about the potential damage caused by underwater noise because we do not hear the noise that well.

### z **Home Page**

All animated graphics by Dan Russell are available under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. 7 https://www.acs. psu.edu/drussell/

### **Suggested reading**


**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

# **Whaling, Seal Hunting and the Efect of Fisheries on Marine Mammals**

*Miko*ł*aj Koss, Martin Stjernstedt, Iwona Pawliczka, Anja Reckendorf, and Ursula Siebert*

### **Contents**



**Suggested reading – 47**

**Supplementary Information** The online version contains supplementary material available at [https://doi.org/10.1007/978-3-031-06836-2\_3].

### n**Learning goals**


### **1 Introduction**

Marine mammals are important top predators in the world's oceans. Many species are opportunistic feeders, catching the most abundant, convenient and easiest caught prey, depending on region and season (. Table 1). For example, Baltic grey seals (*Halichoerus grypus*) feed mostly on herring, sprat and cod in the Baltic Proper, but further north in the Bothnian Bay they also feed on whitefsh and salmon.

Apart from being an important part of marine food webs, marine mammals are indicators for the state of the marine environment. This is one of the reasons why stranded marine mammals undergo extensive postmortem investigations, including stomach content analysis and including monitoring levels of toxic substances in various tissues. Large abundances of whales or seals in certain regions indicate good environmental conditions. For example, decreasing numbers of hauled-out seals could indicate that various



Sources: Bergman (2007) and Rojano-Donate et al. (2018). The food consumption is affected by body weight, diet composition and season

human activities and environment alterations prevent them from thriving. Additionally, if marine mammals maintain a low *fertility rate* (having very few or no offspring) or a high level of diseases in a particular region, it is likely that their environment and prey are contaminated with toxic substances. Common toxic substances are persistent organic pollutants such as pesticides (for example DDT) or industrial chemicals (such as PCB). Similarly, the presence and good health status of marine mammals indicate a marine environment of high quality.

Overlap in human and marine mammal diets can lead to competition and result in bycatch, catch depredation and fshing gear damage. To study such issues, it is essential to know the diet of marine mammals in the area of interest. The identifcation and size of fsh prey can be derived by measuring *otoliths* (fsh ear stones; see 7 Exercise 4.1 and . Fig. 4) often found in the stomach or faeces of marine mammals.

### **2 Bycatch**

Fisheries operate in many areas that are natural foraging grounds of marine mammals. This inevitably leads to interactions and conficts between fsheries and marine mammals. One type of interaction is incidental entanglement and death of marine mammals in fshing gear, called bycatch. Another major issue is gear and catch damage caused by marine mammals.

In the Baltic and North Sea region, bycatch is one of the major anthropogenic threats to marine mammals, although quantitative estimates of mortality in fshing gear are scarce. A few extensive reports suggest that the bycatch rate can be higher than reported in offcial statistics. For Baltic grey seals, the yearly bycatch may be higher than 2300 individuals. For some species, there has luckily been a documented reduction in bycatch: In the 1990s, the estimated bycatch was 7,000 harbour porpoises (*Phocoena phocoena*) in the Danish part of the North Sea. Nowadays, the estimated porpoise bycatch is lower due to altered fshing efforts as well as the use of *acoustic deterrent devices* (so-called *pingers*). Still, bycatch remains one of the largest threats to marine life, including marine mammals, in many regions, including the North Sea and the Baltic.

### **Bycatch**

Incidental catch of non-target marine species in fshing gear. Marine mammals, fshes (non-targeted species and undersized specimens), birds and turtles, as well as invertebrates constitute a substantial part of bycatch in certain fsheries.

The main fshing gear responsible for marine mammal bycatch are gillnets, which are anchored on the sea bottom. Gill nets form very long, nearly transparent walls in the water column, constituting traps for marine mammals and other animals. Unfortunately, incidents of marine mammal bycatch, although fairly numerous in certain regions, are rarely reported by fshermen and not always adequately monitored, which makes a proper assessment of this threat diffcult. Frequently, stranded cetaceans show characteristic net marks around their heads or other parts of the body, indicating previous entanglement in fshing nets (. Fig. 1). Postmortem examinations often reveal a full stomach and bleeding in several organs, most likely caused by death struggle. Net wounds around the neck, snout or fippers are also observed in seals. Even though scientists sometimes judge bycatch as a likely cause of death, they are often unable to obtain information on the location, date and type of fshing gear in which the animal may have been caught. Such data are crucial for the implementation of effective conservation measures for the species in question.

Changing fshing gear to newer types known to be less harmful to marine mammals does not always provide an environmentally responsible or economically feasible solution. For instance, bottom trawling (dragging a trawl over the seafoor) has little direct impact on marine mammals but causes severe damage to *benthic* communities, as well as it may result in a large bycatch of juvenile fsh and invertebrates. Thus, switching to 'marine mammal friendly gear' will not always solve the overall problems.

The worldwide demand for fsh will increase in the coming decades. Due to overfshing and the huge quantity of bycaught and discarded smaller sized fsh, the amounts of fsh obtained by fshing no longer meet the global need. Therefore, most of the fsh consumed today is farm-raised, not wild. Aquaculture is regarded as a solution to the burning issue of ocean overfshing. The main advantage of aquaculture is that, unlike fshing, it relies on bred and harvested fsh, not on depleting wild fsh stocks. Prospects of aquaculture are promising, but some types, such as offshore open systems, pose serious environmental threats, resulting in unhindered interactions between farmed fsh enclosed in cages or netting systems and the surrounding environment. Aquaculture can spread diseases, parasites and chemicals (e.g. antibiotics) into

..      **Fig. 1** Left: Bycaught harbour porpoise with net marks around the snout. © Katarzyna Jęczkowska. Right: Stranded grey seal entangled in fshing net. © Mateusz Puzdrowski

the wild. Faeces and nutrients released into the environment may cause the rise of algal blooms and eutrophication. Damaged cages result in farmed fsh escaping. Escapees of farmed fsh not belonging in a certain habitat can compete for food and place with indigenous species. The escaped fsh can also interbreed with the wild stocks, which may lead to questionable mixing of gene pools. In addition, aqua-cultured fsh needs to eat. To grow them to harvestable size, a large amount of additional smaller fsh is needed, which is usually wild-caught. Thus, there are both positive and negative sides of marine fsh aquaculture.

### **3 Seal-safe fshing gear and catch damage**

Marine mammals can cause catch loss or gear damage by feeding on fsh caught in nets (. Fig. 2). Since the 1990s, the confict has escalated between Baltic fsheries and grey seals. The grey seal population of historically about 100,000 individuals suffered a drastic decline in the 1970s after decades of hunting and exposure to pollution. After being protected in the 1980s, the Baltic grey seal population have recovered, reaching over 40,000 individuals in the late 2010s. Meanwhile, the biomass of several commercial fsh species has decreased in the Baltic for various reasons, and seals have increasingly been perceived as being in competition with fsheries. The seals may affect the fsh stocks not only by directly feeding on them but also through the spreading of parasites, for which seals and fsh are part of the life cycle.

The most severe gear damage and catch loss due to Baltic grey seals is reported from the Gulf of Bothnia. The problems are worst in coastal fsheries using static fshing gear, such as salmon traps, as well as in gillnet fsheries for herring and whitefsh. Fisheries using active fshing gear, such as trawling, are less affected. Various methods have been tested to minimise the seal-fshery interactions. One option is fnancial compensation for seal-induced catch damages. However, this solution is short-term and does not solve the actual problem. Additionally, it does not take the seal mortality in fshing gear into account, unless special constructions preventing seals from becoming entrapped in the gear are used voluntarily by fshers. The implementation of so-called *alternative fshing gear* may both reduce catch and gear damage, as well as bycatch of seals.

### **4 Bycatch mitigation measures**

There are four main approaches to reduce bycatch of marine mammals:


..      **Fig. 2** Marine mammals, in particular pinnipeds, can cause severe catch loss or gear damage by feeding on fsh entrapped in fshing nets. © Annika Toth


The most effective way to curb bycatch is to reduce fsheries that incidentally catch marine mammals. Implementation of he total allowed fshing effort using, for example, gillnets, is nowadays made.

Acoustic deterrent devices of the so-called *pinger* type (. Fig. 3) are effective in minimising bycatch of harbour porpoises. Pingers emit acoustic signals of rather low intensity, with frequencies between 10 and 180 kHz. They are attached to gill nets at a few hundred metres distance from each other. According to EU legislations, fshing vessels above 12 m length using some types of gillnets in certain areas are obliged to use pingers. Unfortunately, gillnets are widely used in Baltic waters, and the areas and gill net types where pingers are mandatory does not always overlap with the areas having the highest abundance of harbour porpoises.

Pingers can almost entirely eliminate bycatch of harbour porpoises, when used properly. However, it is unclear if porpoises habituate to pingers in the long run. Also, pingers may not scare off but instead attract grey seals to the nets. This complicates the effciency of pingers in regions where seals are abundant, since the pingers may act as *dinner bells* for seals and thereby intensify seal depredation. Since seal depredation is already a large problem in the Baltic Sea, Baltic fshermen are reluctant to use pingers. Currently, there are attempts to develop pingers that are inaudible to seals but audible to porpoises.

Temporal and spatial closure of fsheries is another way to successfully reduce bycatch. The deployment of gillnets could be banned during certain times of the year and in locations important for marine mammals. Proper implementation of such regulations requires thorough information on the distribution of marine mammals and an in-depth understanding of the needs of fsheries in the designated area.

Another way to reduce seal-induced catch loss is the development of new fshing techniques. There are different types of alternative fshing gear that have been introduced in the Baltic Sea, for example, *pontoon traps* and *cod pots*. The construction of alternative fshing gear aims to protect the fsh catch from the seals, but also the seals from being bycaught. In addition to new fshing devices and techniques, traditional fshing gear could be modifed by using stronger net materials, and wire partitions or grids in the entrance of traps and fyke nets.

Fish and seafood consumers need to be aware of the impact their *shopping behaviour* have on adequate bycatch protection of marine mammals. Various offcial certifcates have been introduced to ensure that labelled fsh was caught using techniques that minimise bycatch. Choosing a certifed instead of

..      **Fig. 3** Yellow acoustic deterrent devices, so-called 'pingers', are attached to a fshing net in order to minimise bycatch. Harbour porpoises are scared away by the sounds the pingers produce. © Annika Toth

an uncertifed product helps ensure that bycatch caused by traditional and more harmful fshing techniques will fnally be replaced by modern and marine mammal-friendly gear, limiting bycatch.

Seafood certifcation schemes span from self-certifcation to third-party ecolabelling schemes. Some of the most well-known certifcations of fsheries are the international *Marine Stewardship Council (MSC) and t*he *Friend of the Sea (FOS)*. Some countries have their own certifcations, such as the Swedish *KRAV* and German *Naturland*. Out of the 50 or more seafood ecolabelling schemes that are out there, MSC and FOS cover over 25% of the global seafood certifcations.

#### **Seafood certifcation schemes**

The *Marine Stewardship Council (MSC)* assesses if wild capture fsheries are sustainable and well-managed. MSC was established in 1997 as a partnership between WWF and the food company *Unilever*. A certain amount of marine mammal bycatch is accepted under the condition that it is sustainable and only has a small impact on populations. The certifcation is carried out by thirdparty certifers. About 15% of the world's fsheries are covered by MSC programmes. Assessments of fsheries is based on scientifc verifcation of the sustainability of targeted fsh stocks, the ecosystem impact and the quality of management of the fshery. In the future, MSC will adjust its assessment methodology to FAO (*The Food and Agriculture Organisation*, United Nations) guidelines for the ecolabelling of fsh and fshery products.

*Friend of the Sea (FOS)* was founded in 2006 by the Earth Island Institute's 'Dolphin Safe Project', which has been managing the 'Dolphin Safe' label. FOS is one of the most diverse seafood ecolabels and certifes both aquaculture and fsheries. The sustainable fshery criteria require no overexploitation of target stock, not more than 8% discards, no bycatch of endangered species, no impact on the seabed, compliance with regulations, social accountability and gradual reduction of the carbon footprint. The 'Dolphin Safe' label played a role in the reduction of dolphin bycatch in tuna fsheries. Despite these efforts, the affected dolphin populations have not recovered, which indicates that both fshery management and the 'Dolphin Safe' label are not effective enough. Dolphin-safe catch methods may be used by the industry primarily as a marketing tool rather than a genuine attempt to protect dolphin populations. Consumers should look for actual certifed labels on tuna cans rather than general 'dolphin friendly' prints. Also note that some dolphin-safe fshing practises can have a substantial bycatch of other threatened species of, for example, sharks and turtles.

The Swedish *KRAV* label for organic food has implemented a system for the certifcation of sustainable fsheries. Sustainability is evaluated using three criteria: safe fshing methods, sustainable stocks and *traceability*. Safe fshing methods require the use of fshing gear that eliminates capture of non-targeted species or undersized individuals. Sustainability ensures that fshing is carried out on stocks that can be maintained in the long term. Traceability allows checking the location of fshing vessels, ensuring they only fsh from approved stocks in authorised areas.

*Naturland* was founded in Germany in 1982 as an organic farming certifcation scheme. It later developed certifcation schemes for aquaculture and fsheries. Naturland standards on sustainable fshery focus on the careful use of fsh stocks while protecting entire ecosystems, avoidance of harmful fshing methods, and supporting fair working conditions for fshermen.

Seafood certifcation schemes are not without faws. Scientists and NGOs have been objected to some fsheries certifcations. For example, a substantial part of seafood certifed by MSC or FOS lacks stock status information. Target species are sometimes overfshed and therefore not worthy receiving the label. Some of the MSC certifers have been paid by the fsheries. Still, we believe it is sensible to purchase certifed seafood, as the fraction of less exploited or healthier fsh stocks is 3–4 times higher in certifed than in non-certifed products.

### **5 Whaling and seal hunting**

### **5.1 Whaling**

Whaling is the practice of hunting whales, dolphins or porpoises. In some parts of the world, whaling started at least 3,000 B.C., mainly as a food resource. In the 1800s, whales were also hunted for blubber (which was used for, lamp oil, lubrication and soap) and baleen (*whalebone*, used for, corsets and umbrella ribs). During the era of industrial whaling in the twentieth century, many larger whale species were hunted for meat to near extinction. The industrialised hunt had such an impact on populations that several species of large whales are still listed as endangered. Nowadays, whales are protected by several national laws and international conventions. The *International Convention for the Regulation of Whaling* was ratifed by many countries in 1946. Even though most countries have banned whaling, there are still a few countries hunting whales (. Table 2).


..      **Table 2** Examples of modern whaling operations, regulated by the IWC

#### **IWC and ASCOBANS**

The IWC (*International Whaling Commission*) manages whaling and is involved in cetacean research and conservation. The IWC regulates commercial, scientifc and aboriginal subsistence whaling. Membership of the IWC is open to any country that formally adheres to the 1946 Convention. In 1986, IWC implemented a *whaling moratorium* on large whales, pausing commercial whaling. The moratorium has given many whale populations a chance to recover from the extensive exploitation during the nineteenth and twentieth centuries.

The moratorium was affrmed in 2018 and is still effective. A few countries object to the moratorium and pursue whaling, targeting, for example, minke whales (*Balaenoptera acutorostrata*, e.g. Norway) and fn whales (*Balaenoptera physalus*, e.g. Iceland). In addition, some countries are allowed to pursue *scientifc whaling* to evaluate the status of certain populations. However, scientifc whaling has been suspected to be used as a 'loophole' to pursue commercial whaling under the moratorium. Japan is an important country in these discussions. After having conducted scientifc whaling sanctioned by IWC for decades, Japan resumed commercial whaling and left IWC in 2019.

*ASCOBANS (Agreement on the conservation of small cetaceans in the Baltic, North East Atlantic, Irish and North Seas)* was ratifed in 1991 and extended to its present extent in 2008. The objective of ASCOBANS is to restore or maintain a favourable conservation status for cetaceans in the area covered by the agreement. Working groups of scientists and conservationists within ASCOBANS develop area- or topic-specifc management strategies for the protection and recovery of local populations of marine mammals, such as harbour porpoises.

During the twentieth century, the era of industrial whaling, almost 3 million cetaceans were killed. Measured as total biomass, this constitutes one of the largest animal harvests in human history. In the North Atlantic, over 280,000 cetaceans were killed, in the North Pacifc 560,000, and in the Southern Hemisphere an estimated 2,000,000 animals. These are only the offcially documented numbers; the real numbers are likely much higher.

Once stocks of larger whales had been depleted, the whalers moved on to hunt other stocks, and eventually smaller species. Sailpowered whaling ships took around 300,000 sperm whales (*Physeter macrocephalus*) between the early 1700s and the end of the 1800s. Technological advances of the late nineteenth century made whaling extremely effcient. Engine-driven vessels and the *exploding harpoon* were introduced, as well as factory processing on huge ships or at whaling stations. In the frst 60 years of the 1900s, the same number of sperm whales were caught as during the previous two centuries. In the following decade (1970s), the same number of sperm whales were again harvested, this time due to a special interest in the waxy fuid inside their heads, called spermaceti.

### **5.2 Seal hunting**

Seal hunting also goes back several thousand years of human history. Seal bones and teeth are found in human-made deposits in Northern Europe from stone, bronze and iron ages. Seals have been hunted for fur, blubber and meat. They have also been hunted as pest control to reduce competition with fsheries.

During the past few hundred years, the two main target species for seal hunting in Northern Europe were the harbour and grey seal. In the late 1800s and early 1900s, a bounty system was established in several countries as an attempt to reduce seal stocks and their infuence on fshing. The bounty system led to an overexploitation of both species. With the additional detrimental effects of DDT, PCBs and other toxic substances, the populations plummeted in the 1950s and 1960s. Both grey and harbour seals have been protected from hunting since the 1980s in most Northern European countries. Since protection, the populations of Northern European seals have steadily increased, except for a few viral disease outbreaks with a high mortality in harbour seal populations in 1988 and 2002. Today, the abundance of both harbour and grey seals has reached a sustainable level. Still, the nutritional and health status of individual seals have not reached a satisfactory level.

Limited seal hunting (mainly for fshing gear protection, but in some areas also for food) is allowed in several Baltic countries, including Finland, Sweden and Denmark. In Germany, harbour seals belong to huntable game, but they have been exempted from this practice since 1974. Offcially appointed and trained seal hunters help the German authorities to collect dead animals, and to decide if seals in a poor health condition found alive on the beach should be sent for rehabilitation or *euthanised* with a rife.

### **Current topics of seal- fshery interaction research**

#### *Improved Fishing Gear*

Grey seals exhibit remarkable adaptability and cognitive abilities. In regions of high abundance, like the Baltic Sea, they locally create conficts with commercial fsheries by eating fsh from nets and destroying gear. To protect catch, fshermen may replace traditional fshing gear (such as gillnets) with alternative seal-safe gear (e.g. pontoon traps or cod pots). Despite the large progress that has been made in preventing seal-induced catch damage, none of these new types of gear are 100% seal safe. Seals quickly improve their skills in raiding fsh traps, and therefore constant modifcations of fshing gear are essential. It is necessary to continue the development of effective and sustainable seal-safe fshing methods, while at the same time prevent damage caused by seals. In order to improve fshing gear and to test new prototypes, a close cooperation between scientists, fshing gear technologists and fshermen is required.

At the Swedish *University of Agricultural Sciences* (SLU) in Lysekil, Dr. Sara Königson and her student, Jasmine Stavenow, investigate conficts between seals and fsheries. The aim of their research is to develop seal-proof fshing gear. In one of Sara's research projects, she has developed and tested pots as an alternative to gill nets used for cod. Sara and Jasmine attached waterproof cameras to the pots so that they could study both fsh and seal behaviour around the pots. They spent many hours on the pier or in small boats preparing the pots for the experiments, as well as in front of their computers, analysing the footage and summarising the results into reports and scientifc publications. Some of Sara's and Jasmine's seal-proof pots are now commercially available. Sara and Jasmine continue to invent or improve other types of fshing gear.

You can watch the video of their typical day of feld work and a video showing the behaviour of grey seals visiting fshing gear here . Videos S1 and S2.

### **6 Teaching materials**

### ?**Exercise 4.1: Fish dissection and otolith examination**

Did you know that bony fsh have *ear stones*, which can be used for species identifcation? How can you determine the age of a fsh?

Bony fshes have a sensory organ to detect gravity, balance and movement. Within this ..      **Fig. 4** X-ray image of a marine angelfsh showing the location of an otolith (indicated with an arrow). © Frédérich Bruno

organ, the fsh ear is also located. No external ear (such as our *pinna*) is necessary for fsh to hear underwater. Essential to fsh hearing is the *otoliths*, meaning ear- (oto) stones (liths). Each otolith is made of calcium carbonate crystals. Bony fsh have six otoliths, three on each side of the head in posterior end of the cranial cavity (. Fig. 4). Some of them are small, and usually only two of them (which in some species can grow very large, with a length of several cm) can be seen without a magnifying glass. When the fsh is rocked in a sound feld, the otoliths lag slightly behind due to their higher density, and the relative motion between fsh and ear stone is picked up by sensory hair cells.

Otoliths show *annual growth zones*, very much like growth rings on trees. Therefore, they can be used to age fsh. In herring and fat fsh, the annual growth zones can be seen without any kind of special preparation. In other species, such as cod, the otoliths must be prepared before the growth zones are visible. These otoliths are sectioned, polished or washed in weak hydrochloric acid solution in order to enhance the contrast between the different growth zones. Sometimes it is also necessary to break the otolith and burn the cracked surface with a burner or candle before age determination is possible.

There are many other applications to these stones besides age determination. Their toxic content may indicate ecosystem pollution. The growth layer in which toxins are detected may indicate at what age fsh encountered toxins. Otoliths are shaped differently depending on species, and they are therefore used for taxonomic studies and species identifcation. Even though otoliths found in marine mammal stomachs and faeces may be eroded by digestion, they still provide useful information on prey species. Such data can also enhance our knowledge on the magnitude of competition between wildlife and fsheries. Consequently, analysing otoliths makes it possible to study fsh, their predators, ecosystems, fshery interactions and environmental contamination.

In this exercise, you will learn how to remove otoliths from herring.


### z **Tasks**

1. Cut carefully through the top of the head with small scissors and expose the brain. The otoliths are located near the bottom of the brain case.

..      **Fig. 5** (7 Exercise 4.1) Otoliths of different fsh species. The black-and-white scale on top of each otolith is 5 mm long. Fish illustrations under public domain (CC0) © Wilhelm von Wright, Gervais and Boulart


### ?**Exercise 4.2: Whose scat is it?**

Have you ever wondered how scientists determine what aquatic predators eat? Why are dietary studies of marine animals important?

In this exercise you will investigate marine animal scat. You learn how scientists identify marine animals through the help of otoliths and other animal parts found in scat. This information is used to understand the feeding behaviour of marine mammals, their health status, their habitat range, the abundance of fsh and other animals within their local habitat, and much more. For example, in a study from 2013 the scientists used stomach contents to predict how much giant squid is eaten worldwide by sperm whales each year. The result was an astonishing 131 million individuals!

### z **Required materials**


### z **Tasks**

Your task is to identify the consumed fsh species by its otoliths and the bony fragments you found in the scat sample, and to identify the most likely predator by the prey remains present in their scat.


To identify the predator, here is some information on marine animal feeding preferences. **Grey seals**

Often eat herring, cod, haddock, dab, sprat and whiting

Sometimes eat hake, plaice, salmon, crustaceans and molluscs

### **Harbour seals**

Often eat plaice, herring, dab and gobids Sometimes eat crustaceans and molluscs

### **Ringed seals**

Often eat herring, round goby and sprat Sometimes eat crustaceans and molluscs

### **Porpoises**

Often eat herring, sprat, cod

Sometimes eat round goby, saithe and sandeel **Herring gulls**

Often eat crustaceans, echinoderms, herring, mackerel and molluscs

Sometimes eat saithe and sandeel

### **Common guillemots**

Often eat herring, sandeel and sprat

Sometimes eat dab, sticklebacks and whiting **Great cormorants**

### Often eat eelpout, perch, roach and sticklebacks

Sometimes eat common ling, mackerel, molluscs and crustaceans

### ?**Exercise 4.3: Whaling role play**

You have probably heard about discussions about whaling in the news. Did you ever consider why it is so diffcult to pass a ban on whaling, and why some people and nations are opposing it? Should whaling be continued in order to preserve cultural heritage? Can humans use whales as a source of food, just like we use many other types of animals?

Here, in a panel discussion, stakeholders from different interest groups with different opinions debate whether or not there should be a worldwide ban on commercial whaling.

There are very few countries that still pursue commercial whaling. Whale meat for human consumption is usually sold on local markets. The IUCN (*International Union of Conservation of Nature*), the worldwide authority on the status of nature, lists the minke whale, the major target species of whaling, as being of least concern. Countries that are objecting to the IWC's moratorium decision and establish their own catch limits must provide information on their catches to the IWC, while Japan is no longer obliged to report to the IWC as a non-member.


### z **Moderator**

You lead the panel discussion and examine the topic as comprehensively as possible. You should remain independent, neutral and not biased towards one opinion throughout the entire discussion, and you are in charge of controlling a fair distribution of the voiced contributions. You are also responsible for calling the different stakeholders to reason if the discussion gets too heated, and you should encourage active participation by more reluctant participants through direct questions.

To begin the discussion, you ask the participants to present themselves and to outline their position on commercial whaling. Watch the time during the introductions: Each participant only has 2-3 min. If you feel they would have needed more time to explain their views, you can always ask them questions during the debate.

Subsequently, you will start the discussion. Here are some ways to get started:


Make sure to engage all stakeholders in the discussion by giving alternative suggestions or asking about their opinion on that matter. If the discussion comes to a standstill, keep the conversation going. You may, for example:


### z **Stakeholders**

**Whaler:** Whaling is my job. I need to earn my money to feed my family. It is what I learned and what I grew up with. I don't have a university degree or much other working experience; I don't think I could provide for my family if I would have to stop this job. I don't understand why most people are so angry about my job. Compared to what humans do to other food production animals, the whaling I practice is much less harmful. Our modern methods guarantee a quick and humane death. Whaling is sustainable; there are plenty of whales out there in the ocean and the stocks keep growing. The whales have a good life, are free and happy and get killed without any notice. They had a better life and a better death than many animals raised for their meat in farms.

**Pro-whaling fsherman:** Fishing is our livelihood, and the whales eat too much fsh. We are not able to use our fshing quotas any longer due to whales. Fish remains our main export businesses. We need to reduce the whale population in order to fulfl our fshing goals. Some whales even eat fsh directly out of our nets!

**Anti-whaling fsherman:** Fishing is our livelihood, and the whales support us because they are ecosystem engineers. Many people believe that they eat fsh and thus compete with our catches, but that is not true. The larger whales eat plankton and small fsh that is not our target species. They defecate in the water, which enriches the ocean with nutrients and gives small plankton and krill food, which again serves as food source for larger creatures. Whales basically help the fsh—that we want to catch—grow. Additionally, whales that feed on the same species that we fsh always know where the highest fsh abundance is. We just need to go where the whales are and we will have good catches.

**Local politician:** This is a sovereign country making its own decisions. Foreigners do not rule it, and neither does IWC. We decide ourselves whether whaling should be carried out or not. Whaling has a long tradition here, and we are a traditionalistic country. We value our history and our ancestry. Additionally, whaling is sustainable. Why is it OK to slaughter millions of cows, pigs and chickens for food, but not a couple of happy, free-living whales? That is hypocritical.

**Whaling industry economist:** Whaling has a long tradition in this country. My family has been whaling for centuries. Whales have been an accessible, healthy and sustainable food source for decades. Additionally, it is worth a good amount of money to sell whale meat. There still is a demand on whale meat because people grew up eating it. We are a small business, targeting only species that are abundant. Therefore, our practice is sustainable and our takes are not leading to a population decline or extinction.

**The conservationist:** The world's oceans are vast. There is no international police force operating on the high seas. If commercial whaling is permitted to start up again, there will be no way to control international trade of whale meat and blubber. Each large whale might be worth hundreds of thousands of dollars. Illegal and unregulated whaling could once again drive the large whale species to the brink of extinction, just like it happened in the past.

**Animal welfare advocate:** We think that commercial whaling must be halted. No one knows how populations of whales will be affected by hunting, on top of other daily threats they face. Whaling is unethical, and whales are not suitable for human consumption. Whales live long lives and reproduce slowly. They cannot be killed in an ethical manner. Explosive harpoons often miss the right area on the whale's body, subjecting them to suffering a long, slow and painful death.

**Scientist:** Whales have been recognised as ecosystem engineers (their faeces enrich the ocean with nutrients, which feeds plankton and thus substantially supports the bottom of the food chain). Many whales have fxed migration routes, and we often notice that the same animal is mistaken for several. Therefore, populations can be misinterpreted as being larger than they really are. One species may be divided into subgroups, ecotypes or even completely different species, which we are not yet aware of and that we may exterminate through whaling. Additionally, whales are on top of the food chain, and with their extensive blubber reserves and their longevity, they accumulate all kinds of toxins. The accumulation of pollutants in stranded whales can be so high that they have to be disposed as toxic waste. Whaling nations give out warnings that pregnant women should not consume whale meat. This is clearly not healthy food.

**Citizen Robinson:** Only few citizens eat whale meat. I myself grew up never tasting whale meat and I have no ambitions in doing so. Whaling is an outdated tradition that should stop. Many tourists coming here don't like the fact that we are a whaling nation, and we probably have economic losses from people who decide to boycott this country due to our whaling activities. In my opinion, whaling harms our country by degrading its economy and reputation.

**Citizen Johnson:** Whaling is a tradition in this country and therefore we take a lot of pride in it. Many citizens of this nation support whaling because it is sustainable, healthy and good for the economy. Whale hunting creates jobs and provides a locally sourced food source. Also, whale meat is better than farmed meat, because the whale lived a happier life than a cow or pig. Why can't you have both whaling and whale safaris going on in the same country? In Sweden, people are hunting moose, and there are also moose parks where people can enjoy them.

**Tourism expert:** Tourism is one of the most important and fastest growing businesses in our nation. Tourists come to see our nature and also for whale watching. It is absurd that we keep killing whales, but the behaviour of tourists is as baffing to me. Some whale watching tourists even eat whale meat. But other tourists boycott our country as a holiday destination due to our whaling reputation.

### z **Tasks**

1. In this role play, the participants will assume characters of different parties involved in this confict of interest. Choose one of the potential roles (or have one assigned by your teacher) and collect arguments for your position in order to develop a basis for the discussion. Multiple students can form groups of parties. However, make sure that the number of stakeholders in each party of interest is equally distributed. Some additional reading material for more information can be provided by the teacher or obtained from the internet (e.g. the IWC and the IUCN websites). Prepare yourself for your stakeholder position and for possible *counter arguments*. One contestant (teacher or a student) is the moderator of the discussion and should be especially aware of the instructions given above for this role.

	- 5 What is your position on whaling?
	- 5 What are your main arguments?
	- 5 What compromise could be proposed in the interest of yourself or your organisation?

Choose one person of your stakeholder group to represent your party of interest during the discussion.

3. The moderator will start the discussion. Before the panel discussion begins, participants present themselves, their position and their arguments in 2–3 min. All participants are thus given the opportunity to get to know each other and their positions on the topic. After the introduction, the moderator will take the lead on the discussion between the different parties of interest and keep the debate alive.

4. In the end, all students should collectively summarise all pro-whaling and anti-whaling arguments and see if the class can come to a differentiated and objective consensus on their opinion on commercial whaling.

### **Suggested reading**


**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

# **Plastic Debris and Its Impacts on Marine Mammals**

*Katrin Kruse, Katrin Knickmeier, Dennis Brennecke, Bianca Unger, and Ursula Siebert*

### **Contents**



**Suggested reading – 61**

**Supplementary Information** The online version contains supplementary material available at [https://doi.org/10.1007/978-3-031-06836-2\_4].

	- 5 Understand plastic pollution problems in our oceans.
	- 5 Detect and quantify plastics in our environment and everyday products.
	- 5 Obtain knowledge-based ideas to reduce plastic pollution.

### **1 Introduction**

The *United Nations Environment Programme* defnes *marine debris* as "any persistent, manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment." Marine debris consist of many different materials, such as metal, glass, processed wood, and last but not least, plastics. Due to its durability and lightness, plastics make up a large share of all marine debris and can be found also in remote places.

"Plastics" refer to synthetic materials made primarily of crude oil. These materials have many interesting properties, such as lightness and durability. They can be hard, soft, elastic, persistent and formed in any imaginable way. These features make plastics usable almost everywhere. We have a hard time imagining our daily lives without plastics. Plastic materials are used for, for example, clothing and for food packaging and many other products. In the form of nylon, it is also used in fshing nets and fshing lines.

One problem with plastics is that they are not readily *biodegradable*. Together with the large quantities produced, as well as insuffcient ways of disposal and recycling, this means that we fnd plastics everywhere in the environment. In 2020, more than 360 million tonnes of plastics were produced globally. It is estimated that 4-13 million tonnes make their way into the oceans every year. Scientifc expeditions have revealed that more than fve billion pieces of plastic with a total weight of more than 250,000 tonnes are foating around in our oceans. This enormous amount of plastic has severe consequences for marine life. Animals become entangled in drifting garbage and fshing nets, and they confuse plastic items with food. Plastics which have been ingested by smaller animals is transferred to large animals by predation. Different size classes of plastics cause different threats. For marine mammals, studies of the impact of plastics have so far focused on larger debris causing entanglement or ingestion, whereas information on the impact of small plastic items is scarce.

### **2 Plastics: A problem with many sources**

There are many sources of marine plastic debris. A major input comes from land with rivers and beaches. Plastic waste from agriculture, industrial production, construction sites, or from people carelessly dropping waste accidentally ends up in the environment and is transported to rivers and beaches by wind and rain and end up in the oceans. Interestingly, 70% of global debris entering the oceans originate from only ten larger rivers.

Large amounts of plastic debris are mainly caused by poor waste management. But, even in regions with well-developed waste management, debris ends up in rivers and is then transported to the ocean.

Nearly 2.4 billion people (about 40% of the world's population) live within 100 km from the coast. In many countries, waste is still placed in large waste disposal sites that may be situated close to the sea. Strong winds blow large quantities of waste into the oceans. Many plastic items are only used once and then they are thrown away; this includes bottles, bags, cups, straws, and spoons. These items may end in the environment due to the carelessness of consumers or poor recycling systems or problematic waste disposal sites: Even if they are properly disposed in garbage cans, they may still end up in the oceans.

Every time you wash your clothes, thousands of plastic fbers are released into the wastewater. The fbers are too small to be fltered out of wastewater at treatment facilities and therefore make their direct way to the ocean.

Thousands of ships and boats navigate our seas and rivers. Shipping containers may be lost at sea and—although it is nowadays strictly prohibited—rubbish may be thrown overboard. Sea-based sources, including shipping and offshore industry, contribute with 20% of marine debris. During fshing operations, nylon nets, lines and ropes are accidentally lost or dumped at sea. Abandoned fshing nets may stay active catching fsh for a long time period: They are known as *ghost nets*. *Dolly ropes* are orange or blue plastic threads that are used to protect bottom trawling nets against wear and tear. Every year, thousands of kilos of dolly ropes end up in the sea.

### **3 Where does plastics end up, and what are the consequences for marine life?**

Oceanic water is always in motion. Water is transported around by the huge currents that link all ocean basins. Surface and deep ocean currents belong to the same transportation network that work a bit like conveyor belts move water around the world. The atmosphere and the ocean currents infuence one another. Some ocean currents form giant gyres spanning several hundred, even thousands of kilometers in diameter. Once entering the oceans, marine debris circulates in these current systems for decades, perhaps even for centuries, and get concentrated within *gyres* created by the currents.

In 1997, scientists discovered a large area with marine debris in the North Pacifc, named the *Great Pacifc Garbage Patch*. The total weight of all man-made objects in this area was estimated to be 80,000 tons, or the same weight as 500 jumbo jets.

It may take hundreds of years for plastic to degrade. Plastic items are disintegrated into smaller parts by wind and sun. Older objects become brittle and then fragment into smaller and smaller pieces ending at so-called microand nanoplastics. Plastic objects either sink to the seabed or keep foating at the sea surface or within the water column. The weight of foating plastics is enhanced when colonized by small organisms, such as barnacles, mussels, and bacteria. This promotes the sinking process.

The ocean currents transport plastics and its inhabitants over large distances into new regions. Bryozoans, barnacles, hydroids, and molluscs hitch-hike on plastic litter. For *invasive species*, they may reproduce more rapidly in a new area and outcompete native species. This can change the composition of ecosystems and interfere with existing food chains.

During the past decades, scientists have observed impacts of plastic ingestion or entanglement in more than 550 species of marine animals, ranging from invertebrates to mammals. Marine mammals, turtles and seabirds become entangled in discarded fshing gear, restricting the animals in their movements, as well as in feeding or reproduction activities (. Figs. 1 and 2). Marine mammals entangled in submerged and anchored "ghost nets" are unable to surface for breathing and drown. A fshing rope tangled at the base of a tail of a whale can cut off blood circulation and eventually the entire tail.

In the North and Baltic Seas, marine debris cause severe health problems for wildlife. Marine mammals such as harbour porpoises, harbor seals and grey seals have shown a variety of impacts associated with entanglement and ingestion. This includes infammation of organs and suffocation. There has been a drastic rise in the number of reported events during the past decades. Still, there is no satisfactory understanding of the signifcance of marine debris for marine mammals.

Another problem is that many animals mistake plastic fragments with food. By eating plastic fragments, animals may acquire a full stomach without gaining any nutrients—they can starve. Scientists investigated sperm whales which accidentally ended up in beaches along the North Sea in early 2016. In 9 out of 30 whales, a variety of plastic debris was found in their stomachs. The animals had engulfed nets, ropes, foils, packaging material, and even a large plastic part from a car engine (. Fig. 3). One animal was found with 24 kg of marine debris in its stomach.

..      **Fig. 1** A humpback whale caught in a net. The whale was completely covered with the net and one of its pectoral fns was stuck. Several attempts were needed

before the whale could be released. Many whales which cannot be helped die—often because they are no longer able to reach the surface to breathe. © Gary Freitag

..      **Fig. 2** Gannets at a breeding colony on the island of Helgoland. Many Gannets are found dead due to entanglement in net fragments. © Abbo van Neer

..      **Fig. 3** (**a**) A fshing net found in a stomach from a sperm whale, stranded in the North Sea. (**b**) The net was 13 m long. Reprinted with permission from: Unger B, EL Bravo Rebolledo, R Deaville, A Gröne, LL IJsseldijk, MF Leopold, U Siebert, J Spitz, P Wohlsein, H Herr 2016. Large amounts of marine debris were found in sperm whales stranded along the North Sea coast in early 2016. Marine Pollution Bulletin 112(1–2): 134−141

In 2018, a dead young male sperm whale was found with 29 kg of plastic trash off the coast of Spain. A necropsy revealed that the animal had ingested, for example, trash bags, polypropylene sacks, ropes, and net segments. Some months later, in 2018, another sperm whale was found washed ashore in Indonesia. Scientists found hundreds of plastic items in its stomach, including cups, bags, and sandals. In 2019, scientists opened the stomach of a young dead whale in Sicily and found many plastic bags inside. In 2019, in the island of Mindanao, Philippines, a young Cuvier's beaked whale was found having 40 kg of plastic bags, including 16 rice sacks, in its stomach.

Investigating the stomach contents of stranded whales plays a crucial role in understanding the effects of plastic ingestion on cetaceans. However, stranded animals may be diseased and emaciated for other reasons than plastics ingestion and therefore not representative for healthier, free-ranging individuals. Furthermore, animals dying without being washed ashore or investigated, remain unregistered.

### **4 Microplastics: Small particles with specifc problems**

Once in the ocean, plastic waste is exposed to waves, salt, abrasion, and sunlight, breaking up larger objects into small pieces. The materials become brittle and break into smaller fragments. The pieces become smaller and smaller, and at some point they are invisible to the naked eye. However, this does not mean they disappear. Experts assign the tiny particles to different categories according to their size and study their effects on wildlife.



There are many ways that plastics end up in nature. Synthetic fbers are released from clothes when being washed. Tiny plastic beads are added to cosmetics in shower- or peeling gel. Large amounts of these small plastic particles may enter the marine environment. The fragments can be suffciently small to pass flter systems and thus enter the environment. As car traffc increases, there is an inevitable increase in microplastics from tire abrasion ending up in the environment. Scientifc studies show that the abrasion of car tires is one of the largest contributions to microplastics. Almost every part of our mobility sector contributes to the microplastic amount that enters the environment.

Similar to macroplastics, microplastics is mistaken for food by smaller animals. Animals fltering water for plankton, such as mussels, consume microplastics and are unable to digest it. Therefore, plastic fragments are deposited inside the body. When the flter feeders are consumed by other animals, the plastic particles are assimilated inside the predators. They are transported higher and higher up the food webs, where they are found in larger and larger concentrations.

Can 5 mm plastic items affect huge flterfeeding baleen whales? In 2012, high concentrations of pollutants and chemicals added during plastics production were detected in Mediterranean fn whales (*Balaenoptera physalus*). Due to the way of feeding, baleen whales are susceptible to high levels of microplastics ingestion and exposed to associated toxic compounds. In addition, microplastic particles have been documented in the feces of northern fur seals (*Callorhinus ursinus*) and in the digestive systems of stranded dolphins and monk seals.

An additional problem is that seawater contains many *persistent organic pollutants* (POPs) such as DDT and PCBs. The POPs enter the sea via rivers and beaches. They are insoluble in water, and microplastic fragments adsorb these pollutants. As a result, plastic fragments become foating pollutant carriers. Once the particles have been ingested by marine organisms, the pollutants can enter tissues. POPs are usually deposited in the fatty tissue of the organism. These toxic substances can affect the hormone and immune systems, as well as cause cancer. In addition, pollutants enter the food web and are transferred from one trophic level to the next.

Around 99% of macroplastics entering the oceans do not reach a plastic gyre. The plastics eventually break down into microplastics and sink to the sediment. Also, the polar ice contains high concentrations of microplastics that will be released by increased melting due to climate change. Macro- and microplastics have even been discovered in the *Challenger Deep of the Mariana Trench*, the deepest part of the world's oceans.

### **5 Mitigation eforts: What can be done?**

Our attention toward the marine debris problem is growing. Projects for raising awareness in the public are essential for reducing usage and thus risk of disposal into the marine environment. It is important that our behavior and habits change rapidly.

Both NGOs (*non-governmental organizations*) and people being part of different social groups and professions are focusing on the impact of the environment and searching for solutions. Currently, many efforts are focusing on getting debris out of the ocean. Technologies that are trying to clean the oceans, using fltering ships or swimming baskets, are developed globally. These technologies focus on removing macroplastics. There is a more diffcult task ahead of us: to remove microplastics from the oceans, where it makes up the largest portion of all plastics.

An effective method to alleviate the marine debris problem is to reduce plastic consumption. Large contributors to plastic debris that enters the oceans are part of our everyday use. Different ideas to reduce plastics in our wastewater are attempted. Non-wrapped groceries are introduced, offering reduced prices for bringing reusable cups to coffee shops, as well as utilizing only materials which can also be used for other purposes.

Scientists and engineers around the world investigate potential solutions to the debris problem. One focus is on the main sources of marine debris and its trajectories, on its way to the oceans. Another important part of current research is fnding substitutes for plastics, or developing biodegradable forms of plastics while meeting the demands in their usage. However, these substitutes, for example, made from soya or corn, will also generate contamination due to intensive agriculture practices.

Everyone can help to reduce the amount of plastics in the oceans. Use *the three R rules* "Reduce," "Reuse," and "Recycle" to cut down on consumption you don't need. Avoid singleused products like plastic cups or plastic bags. The EU parliament is banning disposable plastic products from 2021, including drinking straws, disposable crockery, and cotton buds. In addition, EU member states are obliged to recycle 90% of all disposable plastic bottles. These rules will give more responsibility to the industry for dealing with plastic waste.

To effectively change attitudes to the use of plastic products, the problem has to be addressed in schools. The issue is already part of the content of a few textbooks, and a larger number of student projects have been established for science competitions that deal with the issue of marine debris. The problems with plastics will last for future generations, which underlines the necessity to educate school children in reducing their plastic consumption.

In recent years, civil engagement in scientifc research has become increasingly important in Europe. In citizen science projects, locals have the opportunity to be part of a scientifc investigation and to advocate for marine protection. The data collected by the participants are evaluated, either by scientists or together with the citizens. They contribute to steering decision-making processes. Citizen science projects also offer great potential for school education. The students are actively part of the scientifc inquiry, deal with a topic and have the opportunity to refect their own behavior and develop awareness.

One example is a citizen science project dealing with marine debris on the yearly *International Coastal Cleanup Day* (ICC). The ICC day is arranged on the third Saturday in September. On this day, coastal sections of rivers, lakes, and oceans are cleaned of debris. Data are collected at the same time, to be used for scientifc purposes.

The ICC day is the largest voluntary marine conservation campaign in the world. For the participating students, it is certainly a positive feeling to be able to contribute to marine conservation. Meanwhile, there is also a smartphone app of the Ocean Conservancy, "Clean Swell," which is currently available in English language only, for the ICC.

### **Current topics of plastic pollution research**

Debris, and especially plastics, have a profound impact on the environment. Many studies have investigated the impact plastic debris has on the marine environment, where organisms of different sizes entangle in debris or ingest it. More recent studies have shown that the majority of debris reaches the oceans by rivers. However, quantities, composition, and sources of debris within rivers or at estuaries have not been well studied and most investigations consider few sampling sites. Sampling a larger area over a longer time span is challenging but may be essential to understanding distribution patterns, transport mechanisms, and sources of riverine debris.

The German citizen science initiative "Plastic Pirates" flls some of these gaps. "Plastic Pirates" involve school children and teachers to sample a river of their choice for different types of debris. The participants use a sampling protocol to document quantities, composition and sources of debris items, and a small net to fsh for microplastics. The data is subsequently sent to a team of international experts for analysis.

The analysis of the frst dataset revealed that about 33% of the collected debris consisted of plastics, and that another large share of garbage is cigarette butts—with a high potential of polluting freshwater. One principal source of debris is people visiting the riverside to meet for having a barbecue or a picknick. Future sampling campaigns with the "Plastic Pirates" aim at investigations of single-use plastics and continue to sample microplastics to cover a larger time span.

### **6 Teaching materials**

?**Exercise 4.1: How diferent debris objects might afect marine mammals**

All kinds of plastic items can become marine debris, and later encountered by marine mammals. Some items found in marine mammals are listed in . Table 1.


..      **Table 1 (**7 Exercise 4.1) Possible threats of marine debris

### z **Tasks**

1: Fill in . Table 1. How might plastic debris items have entered the oceans? Which marine mammal species could be most affected, and why? What are the possible consequences for the species?

### ?**Exercise 4.2: Searching for microplastics in everyday products**

Plastic microbeads are added to many cosmetic and personal hygiene products. The aim is to improve the cleansing effect of, for example, facial scrubs. Although they are very small, microbeads pose a risk to marine wildlife. Due to chemical properties, harmful organic substances can attach themselves to these tiny particles. If they are then mistaken for prey and eaten by plankton-feeders or other animals, they can be absorbed by the organism and in this way enter the food chain.

### z **Required materials**

5 Round microsieve (100 or 300 μm mesh size or coffee flter)


### z **Tasks**


Possible extension:

5. Download the smartphone app "Beat the microbead" or "Codecheck" on your smartphone. Scan your cosmetic products at home and in your local supermarket for microplastics ingredients.


We hardly ever question the fact that we use plastics. Plastic is a synthetic material that nowadays comes in many different forms with all kinds of properties. What all plastics have in common is that they are made primarily using crude oil. Plastics have many practical properties. Plastics have become a daily essential material present in a wide range of products due to several outstanding characteristics. They are malleable, hard, elastic, not very breakable, long-lasting, and can be changed in almost any way. As they can also be produced relatively cheap, they are found all around the globe.


..      **Fig. 4** (7 Exercise 4.3) Estimated timescales for degradation time of different debris items: aluminum can, plastic bottle, paper towels, newspaper, fshing line, cotton rope, wool socks, cardboard box, plywood, Styrofoam plastic cup, milk carton. Try to fll in which debris belongs to which degradation time, from your readings on the internet © Adapted from: World Ocean Review


### z **Tasks**


### ?**Exercise 4.4: Floating plastic**

We will now study the behavior of plastic waste in seawater. This knowledge is essential to fnd out where plastic waste may cause signifcant problems to gray seals in the area. A key question is how plastic waste is spread. Alongside the different types of plastics, its form and density play an important role for its "behavior." This determines whether a plastic object foats on the surface, drifts within the water column, or sinks to the seabed.

### z **Tasks**


3. Develop a series of experiments that you can use to study this property. You can use entire plastic objects or cut out small samples. You can investigate the following questions:

What items foat in the water and how do they behave in water?


### ?**Exercise 4.5: Mystery game**

Situation: In 2016, 30 sperm whales stranded at various North Sea locations. All individuals were young bulls (males) around the same age. Several research groups from the countries being involved are trying to explain the strandings (. Fig. 5).

..      **Fig. 5** Uwe Piatkowski from GEOMAR and Ursula Siebert from the University of Veterinary Medicine Hannover investigating the stranded sperm whales' unfortunate deaths.

### **Scientifc approach**

In addition to experimenting and searching for answers to scientifc questions, the publication of results in specialist journals on the scientifc process and the presentation of the results at conferences are also essential. This step is important to make information accessible globally and to fnd solutions together. In many cases, it is also possible that several research groups are conducting research on the same problem. Every team, of course, wants to be the frst to publish their fndings.

### z **Required materials**

5 Mystery game cards

### z **Tasks**

1. You are one of the research groups from Germany, the Netherlands, France, and the United Kingdom. You and your colleagues will try to fnd a plausible explanation for the stranding in the North Sea by using the cards. Create a logical sequence of incidents, explaining the phenomenon.

Start with card number 7 and use at least fve more. If you fnd a plausible explanation for the strandings, you can publish it.


### ?**Exercise 4.6: Microplastics beach sampling**

Plastics are currently accumulating on beaches worldwide and can pose a risk for many animals. How much microplastic can be found on sandy beaches?

### z **Required materials**


..      **Fig. 6.** (7 Exercise 4.5) Overview sampling points to quantify microplastic fragments on beaches.

### z **Tasks**


### ?**Exercise 4.7: Plastic waste diary**

You are familiar with various plastic products. It is hard to imagine everyday life without them. An average European, for example, uses more than 100 kilograms of plastic each year. The global increase in the consumption of plastic materials has given rise to huge quantities of waste. Think



about how much plastic you use and dispose of every day.

### z **Tasks**


### ?**Exercise 4.8: What can I do?**

Humans have been using rivers, lakes, and oceans since the beginning of mankind. These habitats give us a great deal of resources. But instead of caring for them, we pollute and exploit them. Fortunately, there are also people and organizations who actively campaign to protect the planet. There are many ways of protecting the environments and its inhabitants. Each and every one of us can contribute to that. In order to reduce plastic consumption, you can apply to one or even more of the three R rules.

1. Reduce

Here, the aim is to cut down on things that you do not actually need. Do you really need the latest smartphone or yet another pair of shoes? If you are now thinking about throwing away everything that is surplus to requirements, then this would be the wrong approach. You can get rid of unnecessary items in other ways, such as by getting them to places where they can still be used. Therefore, you should sell, give away, donate, or swap your items instead.

2. Reuse

Before buying something new, why not use something that you already have and spend your money on things that you will use more often? One example would be shopping bags that can be reused many times. If you think carefully on a day-to-day basis, you will fnd all kinds of disposable items that can be replaced with alternatives.

3. Recycle

Separating waste is essential when it comes to recycling. Not all rubbish items can be recycled. In some countries, container deposit schemes, where the consumer pays a small deposit for items such as bottled drinks, which they then get back upon returning the bottles, are an example of where recycling works well.

### z **Tasks**


waste pollution in the oceans so that more people are informed. What initiatives could you carry out so that lots of people get involved? What can people who do not live in coastal areas do to help protect seas and oceans?

You may fnd the following questions useful:

Who produces a lot of waste in your area?

Who is still not aware of the waste problem?

How can we present the results?


Develop a small survey for your school and start to initiate changes to show other pupils that everyone can improve something.

### z **Home Pages**

Ambsdorf J et al. 2017. Meeresatlas: Daten und Fakten über unseren Umgang mit dem Ozean. 7 https://www.boell.de/en/oceanatlas.

### **Suggested reading**


Wohlsein P, Herr H 2016. Large amounts of marine debris found in sperm whales stranded along the North Sea coast in early 2016. Marine Pollution Bull 15112(1–2):134–41. https://doi.org/10.1016/j. marpolbul.2016.08.027.

**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

# **Chemical Pollution and Diseases of Marine Mammals**

*Anja Reckendorf, Ursula Siebert, Eric Parmentier, and Krishna Das*

### **Contents**



**Suggested reading – 77**

**Supplementary Information** The online version contains supplementary material avail**a**ble at [https://doi.org/10.1007/978-3-031-06836-2\_5].

### n**Learning goals**


### **1 Introduction**

Many organic and inorganic chemicals are manufactured by humans and end up in our oceans. As stated by marine scientist C. M. Reddy of the Woods Hole Oceanographic Institution in 2008: '*During the course of the 20th century, the planet became and is now chemically different from any previous time*'. These chemicals are synthesised or formed by natural processes through human activities.

Many different types of human-made compounds cause problems for wildlife. There are toxic *persistent organic pollutan*ts (POPs), which are industrial compounds, and toxic *trace elements*, previously known as *heavy metals*. POPs and trace elements occur in nature in increased abundance because of human activities. Previously, POPs were used as pesticides, industrial chemicals, solvents and pharmaceuticals. They are chemically stable and do not easily degrade through natural processes.

The *biological half-life* describes how quickly a chemical compound (including medications) is reduced to half of its initial concentration in, for example, body tissues. Usually, POPs dissolve well in lipids (but not in water) and are therefore soluble in *fatty tissues*. They are poorly metabolised (and therefore have a long biological half-life). Because they easily bind to the surface of solid particles, they are easily ingested and assimilated as a part of the animal's nutrition. Because of all these features, POPs are prone to dietary accumulation—so-called bioaccumulation, or biomagnifcation—in fatty tissues, with potential adverse health impacts.

With more humans inhabiting coastal regions, the health of oceans becomes a more important issue for everyone. At higher temperatures, POPs volatize and reach the atmosphere, where they can travel long distances before they are fnally re-deposited. Therefore POPs may accumulate also in areas far from their emission, like Antarctica. Hence, environmental contamination by POPs is extensive, and they will often remain in the environment for decades (. Fig. 1).

Marine mammals can be used as early indicators for negative trends and impacts linked to anthropogenic (human-made) activities. Such *sentinel species* will also permit us to better characterise and potentially manage negative impact on human and animal health because of us polluting our oceans.

### **Bioaccumulation of contaminants**

Organisms take in toxic chemicals through contaminated food, water, and/or air. The gastrointestinal tract concentrates ingested stable and hydrophobic (low affnity to water) chemicals. When these substances are stored in fatty body tissues, they increase in concentration inside the organism. This is known as *bioaccumulation*.

#### **Biomagnifcation trough the food web**

*Biomagnifcation* (also known as *bioamplifcation*) causes toxic compounds to be found at higher concentrations in tissues of organisms belonging to a higher level in the food chain. With each step upwards the food web, the concentration of pollutants increases up to ten times in animal tissues. The toxic compounds are transferred from smaller to larger organism, from prey to predator. Because the compounds are easily assimilated but have a long biological halflife, they accumulate within the tissues. The higher the trophic level an animal feeds at, the more chemicals build up within the body. The amount of increase depends on the biological half-life of the substance, and how easily it is assimilated, metabolised or excreted by the organism.

..      **Fig. 1** Illustration of PCB bioaccumulation in the marine food chain. Pollution and the related biomagnifcation within organisms are a global problem. The numbers associated with the shown media/species refer to a

constructed mean contaminant concentration within these, to show the signifcant effect of biomagnifcation. © Guillaume Bolterys

### **Marine mammals and contaminants**

Marine mammals accumulate high levels of toxic POPs and trace elements in their tissues (blubber, liver, hair) because of their unique biological and ecological features:


### **2 The use of marine mammals as bioindicators**

The distribution of chemical pollutants in the marine environment is not homogeneous, and a considerable variation of concentrations may occur regionally and temporally. It may therefore be diffcult to assess the full environmental impact of pollutants. As a supplement to measurements of the contaminant levels at different sites, *bioindicators* can be used to monitor pollution. Bioindicators are living organisms used to assess the levels of pollutants in the ecosystems where they live. Marine mammals are highly suitable bioindicators of the marine environment. Due to their position at the top of the food webs, their long lifespan and the long biological half-time of pollutants, marine mammals accumulate high levels of different toxic chemicals.

The interest in studying contaminants in marine mammals was boosted by past large-scale die-offs or impaired reproduction abilities of pinnipeds and cetaceans living in polluted regions, and the discovery of high contaminant levels in these animals. In many cases, *morbillivirus* infections were the primary cause of disease outbreaks in these animals. Famous examples are the harbour seal mass mortalities in the North Sea in 1988 and 2002. Scientists investigate if environmental pollution plays a role in mass mortalities, as toxic chemicals may suppress the immune system.

### **3 How harmful are pollutants?**

Several chemical pollutants, such as DDT, PCB, TBT (*Tributyltin*) and metallic trace elements, are *endocrine disrupting chemicals* (EDCs), meaning they affect the hormonal system. Hormonal disruptions can infuence many systems in the body, such as the endocrine system itself, reproduction (cause birth defects and developmental disorders), immune cell generation, as well as causing tumours.

Endocrine disrupting chemicals may interfere with the hormone synthesis in the endocrine gland, the hormone transport or the hormone's metabolism and excretion within its target cells. Since many hormones regulate reproductive functions, exposure to EDCs often has negative consequences for reproductive health. Embryos, foetuses and newborns are especially vulnerable to EDCs, causing future problems in brain function, immunity, metabolism and reproductive abilities.

Furthermore, EDCs can alter the synthesis of steroid hormones and have adverse effects on the mechanisms of molecules operated by genes and proteins. Pollutants most likely promote disease and mortality by supressing the immune system. Alterations to energy metabolism can lead to obesity, diabetes, and cardiovascular disease development, as well as have adverse effects on the immune system. Additionally, synergistic effects between various contaminants may amplify the toxicity of different chemicals. Interactions with environmental factors, for example, pathogens, starvation, and climate change (changes in water temperature, pH and salinity) could also amplify the contaminant toxicity and bioavailability.

Trace element pollutants, such as mercury, cadmium, and lead, have especially high cell toxicity and accumulation characteristics. Mercury and PCBs are potent *immunosuppressants* in terrestrial and aquatic animals, altering host resistance to disease. Animals impairments to specifc exposures.

with high contamination levels seem to be more susceptible to diseases than animals with lower toxin burdens. Since EDC effects are usually subtle and more chronic than acute, it is often diffcult to link certain health

### ► **Example**

A well-studied case of contamination effects comes from the St. Lawrence River Estuary beluga whale (*Delphinapterus leucas*) population in Canada. These belugas live at the southernmost limit of the species range, are geographically isolated from other populations and were listed as endangered in 2014 by the *Committee on the Status of Endangered Wildlife in Canada*. Pollution and human disturbance have reduced food resources and caused habitat degradation, which seem to contribute to the decline of this species.

The St. Lawrence River Estuary receives water from one of the world's most industrialised regions. The belugas are heavily contaminated by trace elements, PCB, DDT and PAHs (*polycyclic aromatic hydrocarbons*). Exposure to highly toxic discharges from local aluminium smelters led to elevated contaminant levels in the tissue of the belugas and had toxicological effects. From studies made between 1983 and 2006, 16% of 175 stranded belugas had at least one terminal cancerous tumour. Some of the cancer types found in belugas are related to the presence of PAHs, suggesting that these compounds are involved in the cause of cancer in the SLE belugas.

These effects of pollution are not restricted to belugas only. The human population living by the St. Lawrence River Estuary is also suffering from higher cancer rates than other Canadians.

Contamination is considered a serious threat to the SLE beluga population recovery. Despite reductions in the discharge of some toxic chemicals, pollutant concentrations in tissues do not decrease quickly. Some effects on contaminants may frst develop 20 years after exposure. The belugas could be affected by contaminants for many decades to come. ◄

### **4 Post-mortem examinations**

A *post-mortem examination* is the examination of a dead animal. For humans it is also called an *autopsy*, whereas for any non-human animal it is called a *necropsy*. The aim is to determine the cause of death, how and when the animal died and to obtain a better understanding of how diseases spread. Often, a proper health assessment of living marine mammals is not possible. Therefore, we rely on post-mortem examinations of animals that are stranded or caught in fshing nets to obtain information of animal health and diseases.

Post-mortem examinations elucidate the cause of death and common diseases of the species investigated. We also learn about transmissible pathogens between humans and animals (so-called *zoonoses*) and the infuence of anthropogenic activities on wildlife. Additionally, necropsies are the main source of samples used for toxicological analysis, which helps researchers to associate contaminant loads with clinical observations and pathologic health impairments. This helps us to identify how different pollutants and their concentrations affect the health of marine mammals.


For a small animal such as a harbour porpoise (*Phocoena phocoena*), a necropsy lasts 2-4 h, depending on the animal's decomposition status. For a larger whale, necropsy may last for several days, depending on available work force and technical equipment, as well as the stranding location.

Some extra examinations can be undertaken depending on fnancial means, which species is investigated, and under which circumstances it was found. Additional examinations may include *immunohistology* (the microscopic study of tissues with the aid of antibodies that bind to tissue components and reveal their presence), *electron microscopy*, bone density measurements, and analysis of stomach content and reproductive organs. Such examinations are complex and time consuming, and analysis may take several months.

The cause of disease and death may be determined, and the general health status of the individual can be assessed. This may also inform the health status on the population and the habitats frequented by the animal. However, it is not always possible to determine a cause of death. Some cases remain unsolved even after a thorough post-mortem examination.

Disease can be a major cause of population decline in marine mammals, and the reasons for many stranding events remain poorly understood. New sequencing technology, virological and microbiological studies can identify pathogens and diseases and help in surveillance.

For watching a short video about the necroscopy of a harbour porpoise, see: (7 https:// wissen.hannover.de/en/Institutions/Universityof-Veterinary-Medicine-Hannover/Lookinginto-Animals-Necropsies-at-the-TiHo).

### **5 Common diseases of marine mammals**

Marine mammals, just like any animal, can suffer from different kinds of diseases. These can affect their health adversely, cause pain, distress and even death, and therefore have negative implications for the entire population.

Diseases can be caused by different reasons:


For any cause of disease there is often secondary bacterial and parasitic infections, most common in the lungs.

A high load of parasites (e.g. pulmonary roundworms, *gastrointestinal nematodes* and tapeworms, liver and *gastric fukes*), pneumonia, acute traumata (from bleedings or fractures), chronic disease and direct anthropogenic impacts are common for stranded marine mammals**.** Impaired hearing, as well as disruption of the hormonal and immunological system, can also have severe, adverse impacts on individual health.

Chemical pollution may play a role in the *pathogenicity* (the ability of an organism to cause disease) of several types of diseases of marine mammals. Pathogenic viruses have been associated with meningitis, bronchopneumonia, skin diseases and changes in the reproductive system. Different infuenza A virus strains have caused at least fve larger die-offs of seals in the past 40 years. There is a risk that these diseases can be *zoonotic* (being able to transfer to and infect humans).

A deteriorated health status from an increased pollutant burden can lead to devastating viral epidemics. Huge morbillivirus die-offs were caused by the *Phocine Distemper Virus* (PDV) in 1988–1989, 1990–1991, and 2002 in harbour seals in the North Sea and Kattegat, and by a dolphin morbillivirus in 1990–1991 in striped dolphins (*Stenella coeruleoalba*) in Mediterranean waters. The *epizootic* (disease event in an animal population, analogous to an epidemic in humans) PDV outbreaks killed thousands of animals, and the disease susceptibility of the infected individuals was probably caused by contaminantinduced *immunosuppression*.

Exposure to a mixture of different PCBs decreases the immune response and increases the risk for virus infections. If other environmental factors also favour virus replication and their rapid spread, combined effects may lead to epizootic outbreaks. Furthermore, PCB exposure indicated a contaminantrelated disruption of hormone function of free-ranging harbour seals and harbour porpoises, leading to reduced reproduction.

### **Contamination in the Baltic Sea from the 1970s and 1980s**

Elevated POP levels in Baltic grey seals (*Haliocherus grypus*) and ringed seals (*Pusa hispida*) in the 1970s and 1980s were linked to reproductive failure and several different tissue lesions, causing the so-called *'Baltic Seal Disease Complex'*. Affected seals had smaller *thyroid glands* (responsible for secretion of hormones regulating growth and development) and enlarged adrenal glands (producing a variety of hormones, including adrenaline, cortisol, and sexual hormones). The uterus experienced *stenosis* (abnormal narrowing), *occlusion* and tumours, resulting in impaired reproduction. There were also claw lesions, loss of bone structure in the skull and reduced bone mineral density.

High concentrations of organochlorine are associated with a low mineral density in *trabecular bone* (porous, internal skeletal bone tissue found at the ends of long bones, in the pelvic bones, ribs, skull, and vertebrae). Measurements of bone mineral density provide insights into the bones' health and can determine the risk for fractures. Severe intestinal ulcers and increased parasitic burdens have also been associated with high loads of DDT and PCB.

Zoonotic diseases can be dangerous for people encountering dead or sick marine mammals. People working with marine mammals have the highest risk of acquiring zoonotic diseases. Therefore, marine mammal researchers, rehabilitators, trainers, veterinarians and volunteers must be extra careful. People encountering captive or wild marine mammals during, for example, vacations should also be careful. Zoonoses caused by bacteria, fungi or viruses are easily transmissible. Luckily, the majority of transmissions from marine mammals to humans have only resulted in localised skin infections that can resolve spontaneously or with appropriate medical therapy. However, some zoonoses can lead to life-threatening systemic diseases. When encountering dead or alive marine mammals, always keep a safe distance and call appropriate authorities.

Growing amounts of anthropogenic infuences and utilisation of the marine ecosystem constantly increase the pressure on marine mammals, their habitat and the associated stress and disease risk. Marine mammals may face more infectious diseases in the future, enhanced by the prevalence of contaminants in the environment and in the food chains.

### **Current topics of chemical pollution and diseases of marine mammals research**

Chemical pollution affecting marine mammals is an important topic for current research, since it includes many unanswered questions. Even though there is knowledge on intake pathways, bioaccumulation and biomagnifcation, as well as on geographical and temporal contaminant trends, data is lacking on the implications on marine mammals.

There have been many questions regarding the impact of plastics and other debris on the marine fauna, including marine mammals. This includes the transport of contaminants to coastal ecosystems (persistent, bioaccumulative and toxic chemicals attach to plastics) and impacts of macro as well as micro plastics. It is still unclear if ingested plastics add signifcantly to the existing contamination load. Plastics are nowadays such an important topic, so that this book dedicates a whole chapter to them.

Many studies are conducted on diverse species and different known and measurable pollutants. However, this does not mean that all potential pollutants are known and tested for. There is still a wide grey zone of unknowns, including newly emerging contaminants, their accumulation within the environment, impacts they have on different species, and potential human exposure.

Many of the current studies on cetaceans focus on organochlorine contaminants and their reproductive implications, particularly in endangered species and subspecies, since they are especially vulnerable. This focus may change over time with new analytical methods. Orcas are on top of the trophic food chain and a very long-living species. Thus, they are highly susceptible to contaminant biomagnifcation and consequential reproductive impairment, since immunosuppression can have detrimental effects on offspring (embryos during pregnancy, calves receiving large amounts of contaminants through nursing) and population survival.

*Stable isotopes* and *biomarkers* are used to assess contaminant exposure as a feeding ecology tool and to assess the bodily response to environmental pollutants. Stable isotopes are non-radioactive variations of chemical elements. Measuring and analysing their distribution, amounts and proportions in samples can be used to trace the origin, history, source, chemical interactions, and carbon and nitrogen cycles of the studied sample. Biomarkers are characteristic biologic traits that can indicate normal or pathogenic processes associated with stress (e.g. environmental pollution or diseases) within organs, cells, genes, gene products, or hormones of the studied organism. Since the primary reason for wildlife contaminant exposure is their feeding ecology, effective new tools for diet determination and habitat use are key elements of many eco-toxicological studies.

Another important topic for current research is the individual and population health effects of oil exposure on marine mammals. An example is the extremely long and large oil spill caused by *Deepwater Horizon* in the Gulf of Mexico in 2010. Many cetaceans have succumbed to different disease complexes associated with the spill and suffered from reproductive failure and abortions. Establishing a link between the massive oil spill and its effect on wildlife is crucial for preventing future disasters and establishing appropriate management plans for similar human activities.

We need to consider effects of both older pollutants such as PCBs, which are banned in Europe and North America but are still long-lasting in the food chains, as well as newer chemical pollutants. We need to improve pollutant management and design effective conservation measures. It is also crucial to develop sampling and analysis methods for new contaminants, to generate new mitigation measures to prevent further contamination, as well as develop functional cleaning methods. Last but not least, we need to tackle these issues on a global scale to prevent further entries of pollutants into the environment.

Apart from PCBs and trace metals, pharmaceuticals (including human and veterinary drugs) are another important class of contaminants entering the world's waterways. Thousands of tons of pharmacologically active substances are used annually worldwide. Unfortunately, they receive relatively little attention as possible environmental pollutants. Up to 90% of consumed pharmaceuticals can be excreted unchanged, while environmental bacterial action can convert utilised metabolites into active drug compounds. Additionally, unused medicines are often disposed through the sewage system, and many pharmaceuticals are only incompletely eliminated at sewage treatment plants. The possible effects of the presence of drugs in aquatic systems are widely unknown.

A major concern has so far been that antibiotics found in effuent sewage may cause increased resistance among bacterial populations exposed to these drugs. There are currently several studies looking for multidrug-resistant bacteria in marine life. However, most aquatic organisms are continually exposed to a whole range of different substances. Especially in coastal regions, pharmaceuticals may suppress the immune response and hormone production of aquatic organisms.

Several studies have shown that many aquatic animals are affected by marine environment polluting drugs: Oysters from two different bays in Canada contained traces of medications such as antibiotics, *antihistamines* (used for allergy treatment) and pain relievers. 'Intersex' fsh, with both male and female reproductive organs caused by *endocrine disrupters*, have been found worldwide. Scientists believe that artifcial hormones from birth control pills may contribute to this problem. *Antidepressant* and *antianxiety* medications are also found globally in the environment. They accumulate in wildlife tissues, and their potential to disrupt normal biological systems and behaviours is extensive.

Many aquatic organisms spend their entire lives in polluted environments, affecting their immune system, feeding habits, behaviour, metabolism, and movement patterns. *Prozac* (a common antidepressant used for the treatment of depression) causes shrimp (*Echinogammarus marinus*) to leave their natural, hidden habitat and head towards more luminous locations, making them vulnerable to predators. Small amounts of cocaine can have adverse health effects on critically endangered European eels (*Anguilla anguilla*). Cocaine-exposed eels were hyperactive and suffered from muscle damage. These problems do not end in our rivers or oceans: When we eat seafood, the pharmaceuticals and contaminants return to our bodies, affecting our physiology and starting a new vicious circle.

### **6 Teaching materials**

### ?**Exercise 5.1: How can diferent types of pollution afect marine mammals?** Have a class discussion:

5 Identify sources of, and solutions to air pollution.


### **Tip**

Let the students collect all discarded items they fnd on their way to school. Discuss the potential the objects have to harm wildlife.

Some activities anybody can do to help reduce pollution:


Be sure to share facts that will emphasise the importance of your activities and why you are doing them. For example, when you are recycling, explain that recycling just one glass bottle reduces air pollution by 20 percent and causes 50 percent less water pollution compared to making a brand-new bottle.

### ?**Exercise 5.2: Mussel fltration**

Organisms get rid of contaminants through catabolism and excretion, but how does the ocean get rid of pollutants?

In this experiment, we will demonstrate the important role of mussels as waste collectors within aquatic ecosystems by showing their ability to clear water.

Marine mussels are *bivalve* (they have two hard shells) molluscs. There are among other species, blue mussels, oysters, and clams, which all improve water quality and contribute to healthy marine habitats. They play an important role in aquatic ecosystems. Mussels are flter feeders. They draw in seawater and flter out phytoplankton and sediments. A video showing the anatomy of a mussel can be found at 7 https:// www.youtube.com/watch?v=gZKSFBj- - FqU.

On this 3D animation 7 https://www. youtube.com/watch?v=7KekxV78gns you can observe flter and particulate organic matter fltration by a blue mussel (*Mytilus edulis*). The animation shows the path of water (blue) and associated food (orange) in the mussel. Siphoned material is either transferred to the mouth for digestion or sloughs off the gills and exits via the ventral margin of the shell. Digested material is used both as fuel for various life processes and excreted as faeces. The amount and rate of particulate matter removed from the water column and subsequent deposition of waste depends on species, size, water temperature and particle concentration.

Marine mussels function as bioindicators of marine pollution. As sedentary suspension feeders, mussels remove a variety of materials from the water column. These materials include pollutants that can be assimilated and bioaccumulate in their tissues.

### z **Required materials**


bour (if blue mussels cannot be obtained, freshwater mussels from a lake or aquarist stores are also an option).


### z **Tasks**


After the experiment, the living mussels should be returned to their place of origin, or they can be kept in suitable aquarium; or a dissection can be done to view the food colouring deposition within the mussel by colouration of the organs. While the mussels are alive, you can observe the ciliary movements at the level of the gills with a binocular microscope. You should, however, consider how to humanely kill the mussels prior to dissection, for animal welfare reasons. This can be done by boiling, by bubbling carbon dioxide or adding a 20–30% concentration of magnesium sulphate into the water. Please do NOT use formaldehyde or alcohol for euthanasia purposes.

You can also watch a recording of the whole mussel clearing experiment 7 (Video S1).

..      **Fig. 2** (7 Exercise 5.2) Mussel fltration experiment. The upper picture shows two aquaria with sea water, the right one also contains mussels. The bottom picture

### ?**Exercise 5.3: Bioaccumulation: The hidden dangers in the food web**

The processes of bioaccumulation and biomagnifcation are connected. How can we visualise a better understanding of these concepts?

With this simple experiment, students can observe how contaminants accumulate and magnify in different organisms within the food chain. Through ingestion with their prey, chemicals move up through the food chain. Bioaccumulation means that even when the initial level of chemicals was low, the concentration accumulates in organisms higher up the food web, increasing their toxic potential.

shows that after 11 min, the mussels have cleared the water completely, while the tank without mussels remains unchanged

### z **Required materials**


### z **Tasks**

Place all 30 items in the 'shaker' to represent the population of primary producers and give it a good shake. Record the amounts of DDT

..      **Fig. 3** (7 Exercise 5.3) Top: game requirements (differently sized cups, a 'shaker' and 'plankton' items of two different colours); Bottom: playing the game—simulation of bioaccumulation by emptying the contents of two randomly chosen small 'sand lance' cups into one of the medium 'cod' cups

(number of, for example, red sweets) per producer (for example, 10 contaminants per 30 producers gives a total of 1/3)


Empty the contents of two randomly chosen 'cod' cups into the large 'porpoise' cup. Record the amount of DDT in the porpoise.

4. Place all items back into the 'shaker' cup and repeat the experiment two more times. Then calculate the average amount of DDT for each organism from all three trials.

Draw conclusions to marine life by using the following questions:


Herring, Squid, Salmon, Mackerel, Orca, Mussels, Shark, Cod, Tuna

?**Exercise 5.4: Oil spill clean-up (Part 1)**

Imagine an oil spill into a body of water what methods or materials could be used to clean up the oil?

The ocean has been subject to many different small oil leakages and large oil spill disasters with major environmental impacts. There are chronic spills: The Niger Delta is polluted by over 13 million barrels of crude oil, with an average yearly spill of 240,000 barrels. More commonly, we hear about wrecked oil cargo ships such as the 'Amoco Cadiz' crude oil carrier spill in France in 1978 and the 'Exxon Valdez' oil tanker spill in Alaska in 1989. In this exercise, you will model an oil spill, look at the impact of oil on seabirds and test different materials for cleaning up the spill. This experiment will help you understand why an oil spill is an environmental catastrophe and a diffcult task to deal with.

### z **Required materials**


### z **Tasks**

First, you have to prepare your clean water and 'crude oil'.

	- 5 What happened to the oil when you dropped it on the ocean? Record your observations and explain them.

4. To test the sorbents each student should choose ~3 sorbents to test, so that all available options are being tested. Before starting, write a hypothesis on how the different sorbents you selected will clean up oil and which of them will work best.

Test the sorbents one at a time and record your observations thoroughly.


Look back at your original hypothesis and write a concluding statement that recommends materials and methods for cleaning up oil spills based on your fndings.

*Oil spill clean-up (Part 2)*

How are animals affected by oil and related clean-up methods?

	- 5 What is the function of feathers for birds?
	- 5 Which water bird species can you think of being affected by oil spills?
	- (a) Cold water washing: try washing some of the oiled feathers in cold water. Write down your observations.
	- (b) Hot water washing: try washing some of the oiled feathers in hot water. Write down your observations.
	- (c) Washing with detergent: try washing some of the oiled feathers in the warm soapy water. Write down your observations.

*Oil spill clean-up (Part 3): Group discussion*

Discuss the following points within your class and perform some online research yourself on the issue:


sible resultant liver and kidney damage. However, cleaning (restraint and handling) is a very stressful procedure for a wild bird—should birds be cleaned immediately after capture or should they not be washed until their physical and mental condition is stable (such that they are likely to survive the procedure) even if that increases the chances of intoxication through toxin absorption?

5 Why is it so important to make sure the bird is thoroughly rinsed and defnitely clean after the washing procedure?

*Example* a*nswers*:


### ?**Exercise 5.5: Greenhouse gases in the ocean**

It is often mentioned that the ocean functions as a huge CO2 trap, which is of major importance for climate regulation, but how does it do that?

The ocean absorbs gases from the atmosphere and releases them again. Thus, the world's oceans have a major infuence on the world climate and also absorb a lot of airborne contaminants. Gases like the greenhouse gas carbon dioxide or other pollutants can dissolve in the water, just


ment.


### z **Tasks**

Fill half of the bowl and the bottle to the brim with warm tap water. For a nicer optic, you can dye the water with food colouring.


What does this mean for other pollutants and for aquatic animals?

If you are unsure, perform an online search on sea temperature increase and its effects on ecosystems.

### **Explanation**

In this experiment, we have to discern the invisible from the visible gas bubbles: not all the produced gas arrives at the top of the bottle, because—invisible to us—a certain portion is absorbed by the water. The gas basically 'dissolves' in it. The ability of the water to absorb gases depends on the temperature and the amount of gas already dissolved in the water: the colder the water, the more gas can be absorbed, resulting in a smaller gas bubble within the bottle (Step 2). The second effervescent tablet (Step 3) then dissolves in water, which already contains a lot of gas from the frst trail (it is almost 'saturated'). Therefore, a much larger proportion of gas directly fzzes into the bottle now.

In the past, water in the world's oceans contained relatively little carbon dioxide, and large quantities of greenhouse gases could therefore pass from the air into the water at the ocean surface. Meanwhile, our oceans slowly begin to warm due to climate change caused by carbon dioxide. Due to both effects (saturation and temperature increase), the oceans are less able to absorb this gas. It is a vicious cycle.

### **Suggested reading**


health. London: Elsevier, Academic Press ISBN: 9780128122501.


Doeschate M, Esteban R, Ferreira M, Foote AD, Genov T, Giménez J, Loveridge J, Llavona Á, Martin V, Maxwell DL, Papachlimitzou A, Penrose R, Perkins MW, Smith B, de Stephanis R, Tregenza N, Verborgh P, Fernandez A, Law RJ 2016. PCB pollution continues to impact populations of orcas and other dolphins in European waters. Scientifc Rep 6:18573. https://doi.org/10.1038/srep18573.

**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

# **How to Become a Marine Mammal Scientist**

*Katrin Knickmeier, Anja Reckendorf, and Dennis Brennecke*

### **Contents**


### n**Learning Goals**


### **1 Introduction**

There are many ways to become involved working with marine mammals as a professional career. You can become a zoologist, marine or population biologist, oceanographer, veterinarian, ecologist, physicist, engineer, underwater photographer, technician, national park ranger, naturalist, professional scuba diver, digitalisation expert, science communicator, project assistant at an institute studying marine mammals or a combination of several of these. Scientifc working with marine mammals is transdisciplinary and encompasses various academic disciplines, such as biology, chemistry, physics, mathematics and engineering. An interest in topics relevant for today's environmental challenges (e.g. climate change, pollution, decrease in biodiversity, renewable energy, natural disasters and food security) can lead to studies of marine mammals. Marine mammals have a fundamental role in many marine ecosystems.

### **2 Marine mammal career opportunities**

If you plan to become a marine mammal scientist, it will require your full devotion, time, energy and creativity. Practical feld work outdoors can be equally part of a researcher's job as working on the computer or performing meticulous laboratory work. Try to fnd a good place to gain experience in your feld of interest and a team that will give insights into their daily work. Volunteering can be important to gain knowledge and experience for a future career. If you are unsure about a certain job or work feld, receiving practical insight often helps to make the right career choices for your future. For example, you could utilise your holidays to familiarise yourself with an occupation of interest, like participating in aquatic animal censuses, rehabilitation or education programmes.

There are thousands of students who want to work with marine mammals. Since you are not alone in your passion, you have to be unique in some relevant way. You can achieve this by learning certain technical skills, such as computer coding, equipment repair, or by acquiring a scuba certifcation, a boat handling licence or a permit to fy drones or radio control aircrafts. It is also important to educate yourself by reading specialised and scientifc literature. You can read about marine animals that interest you, but also about your specifc feld of interest, such as diving physiology, acoustics, diseases, social behaviour, prey species and food availability.

### **2.1 Prerequisites learned in school**

Most research positions have an academic background, so achieving good grades especially in the natural sciences, technology and mathematics is important for being accepted into a university to study your feld of interest. It is important that you are profcient in English. You can improve your language skills through training courses. Scientists regularly present their research at international conferences or meet during different assemblies to exchange knowledge, project ideas and research outcomes. Meetings are almost always held in English. You report your study results in scientifc publications, written in English to reach a large audience.

In some parts of the world, many people you meet are not comfortable speaking English, so you also want to pick up other languages. Latin is not a requirement, but numerous scientifc terms like taxonomy or anatomical structures are Latin for global standardisation.

### **3 How to become a marine mammal scientist**

There are many university programmes preparing you for a career in science, some of which will be touched on in this chapter. Also, non-academic professions can lead to an active career in marine mammal science and research. Scientifc groups rely on employees with many practical and administrative backgrounds, such as laboratory technicians, secretaries, communication specialists, public relations managers and animal trainers.

### **3.1 How to become a marine biologist**

Marine biologists study marine organisms, which may include either microscopic beings such as plankton, or larger animals such as marine mammals. If you want to study these organisms you may either observe them in the feld (that is, in the ocean), or you can collect some individuals and bring them into your laboratory. In the laboratory, you can investigate a certain scientifc question, for instance whether a certain species can survive summer heat waves, by simply increasing the temperature of the water simulating a heat wave event. During feld studies, you may investigate if marine mammals are more present in pristine areas than highly human impacted areas.

To become a marine biologist, you need to gain knowledge in a broad range of disciplines. These mainly constitute the subjects of biology, chemistry, geology, physics and mathematics. Being engaged and achieving good grades in secondary school is important. Marine biology and all related careers are of a high educational level, which means you likely need to obtain a degree from a college or university to become a competitive candidate for a job.

First, you likely will need to get a university degree, which is often a *Bachelor of Science* in biology or any other natural science. There are different university programmes, like environmental sciences, marine geosciences, bioinformatics, etc. The duration of a Bachelor's programme is usually three or four years (six to eight semesters). After obtaining your degree, you can choose a feld of special interest and deepen your knowledge by entering a *Master's programme* to study and specialise in, for example, marine biology, marine environmental sciences or biological oceanography.

A Master's programme usually lasts four semesters (two years) or in some countries three years. The fnal year or semester is dedicated to your Master's thesis, for which you choose a research topic that interests you and that you would like to focus on in your future career. Keep in mind that almost everything in the marine environment is connected and therefore of relevance, from the tiniest plankton to the largest animals on Earth, and a solid basis of knowledge is needed to understand them and any threats they face.

After completing a Master's thesis, you may continue to pursue a doctoral degree, which will give you the opportunity to develop your own research questions, and then by performing experiments or feld surveys, write scientifc publications and thus become a part of the scientifc community. This last phase of higher education usually lasts at least three to four years, sometimes longer.

### **3.2 How to become a veterinarian**

If you would like to become a veterinarian, you should have a general understanding of mathematics, physics, chemistry and biology. You should be interested in domestic animals, animal health, microbiology, diseases, food safety and hygiene. If you want to become a wildlife veterinarian, you should also be interested in wildlife, environmental protection, animal welfare and conservation.

To be accepted by a veterinary university, you usually need to have good grades in secondary school, especially in the natural sciences. Often, a letter of intent and an aptitude test are also required. The educational system differs depending on your country of residence, but it usually takes some 11 semesters (5.5 years) of study, including compulsory practical internships. You learn about zoology, botany, chemistry, physics, biochemistry, embryology, pharmacology, as well as more specialised topics in anatomy, physiology, pathology, animal welfare, internal medicine and surgery. You also learn about food and meat production and hygiene.

Depending on the university, you may specialise in a certain animal species during the course of study. Even so, with a veterinary degree you have a broad training and can work in many different felds. You can work in a veterinary clinic, in the food production and hygiene sector, pursue research, sell veterinary supplies, or work for the pharmaceutical or another industry. Unfortunately, there is usually little university training in topics of interest for wildlife veterinarians. You need to gain experience through internships and postgraduate studies to specialise in felds like wildlife biology, zoo animal and wildlife health, animal welfare and conservation.

As a veterinarian you are expected to see the larger picture by connecting fragmented information to form a diagnosis, to function in unfamiliar situations, to work reliably under stress and to quickly familiarise yourself with new situations and areas of work. You need to be attentive and creative, because regardless of whether you are treating a mouse, horse or elephant, you have to fnd a solution for each animal and situation. In addition, you can specialise in clinical felds such as reproduction, *ophthalmology* or dentistry rather than in an animal species. If you desire to work with marine mammals, you should try to engage in as many practical experiences as possible. Volunteer wherever you can and participate in relevant internships. This is a highly competitive feld with very few paid positions. Therefore, you should be determined and excel at your profession to succeed in the long run.

In rehabilitation or permanent holding facilities, the veterinary care team obtains regular hands-on experience with the animals they care for. Veterinary specialists are often called in for their expertise to assist the head veterinarian with clinical cases (such as dental reconstructions, or *osteosynthesis*). For some wildlife veterinarians, marine mammal research often involves little hands-on work with the animals, as much of the work focuses on population levels or the pattern of spreading of a disease. One should be prepared for working many hours on a computer or in a laboratory. Still, working as a veterinarian is highly rewarding, whether it is helping individuals in a clinical setting or performing wildlife research on a broader scale, as in this profession you can usually see the results of your devotion and you can do a lot of good.

### **3.3 How to become an engineer**

*Advice from Principal Research Fellow Mark Johnson, PhD in electronic engineering, Scottish Oceans Institute and Marine Bioacoustics Group, University of St Andrews, and Aarhus University, Denmark.*

Working on engineering methods to study marine mammals is incredibly rewarding and challenging. Most marine mammals spend little time at the surface, so much of what we know about their behaviour and capabilities comes from using electronic data loggers (records data over time and/or in relation to location). To learn something new in this highly specifc feld, you have to develop a logger capable of measuring something different or invent a way to analyse the data that the loggers collect, and this often requires engineering knowledge. Engineering is both a set of skills and a way of looking at problems. Engineers use maths and physics to understand how things work or to build new things. In animal biology, engineers invent ways to fnd out where animals are, what their environment is like, how many of them are there, and what they are doing. Some biologists working with animals take an engineering approach, for example, by applying physical models to explain how animals move or how the sounds they make radiate into the environment. Either way, the key is to look at problems from an engineering perspective and acquire enough knowledge in maths, physics, and engineering to develop the mechanical or electronic systems you need.

Many universities offer Bachelor's degrees in engineering in which you usually have to select between mechanical or computer and electronic themes. Some universities offer more cross-disciplinary themes such as industrial design or biomedical engineering which may also give you useful skills for developing systems to study marine life. A more practically oriented diploma in computer engineering may also be a possibility to help you add engineering skills to your biology training (e.g. as an evening class). There are few research groups actively working on engineering applications in marine biology, and you may need to persuade researchers across departments at your chosen university to create a cross-disciplinary opportunity for postgraduate study. However, there is such a powerful need for people with engineering skills in marine biology, that you may fnd that researchers are keen to create such opportunities.

Strangely, many university engineering courses do not teach you how to build electronic devices. They teach you about the theory and less about the practice. Most engineers learn about designing and building by trial and error or by working with other engineers. Some companies employ interns and this can be a good way to learn how to proceed. Another way is to reverse engineer: see how other people have designed equipment and try to adapt their work. There are a lot of hacker and engineering communities on the web that can help with advice (albeit of varying quality). But ultimately, the way to learn is to build things, test them and fnd out what breaks, repeatedly.

### **3.4 How to become a mathematical biologist**

*Advice from Dr. Benno Wölfng, formerly responsible for statistics and modelling at ITAW, now working in the division for Management and Monitoring of Marine Protected Areas of the German Federal Agency for Nature Conservation, Isle of Vilm, Germany.*

In his autobiography, Charles Darwin 'deeply regretted that [he] did not proceed far enough at least to understand something of the great leading principles of mathematics; for men thus endowed seem to have an extra sense'. This *extra sense* has facilitated great scientifc discoveries in life sciences in recent years. On the one hand, mathematical models are excellent tools for studying complex systems such as the evolution and spread of new traits in a population or the spread of disease. On the other hand, statistical methods are essential for quantifying the evidence in favour or against a scientifc hypothesis and thus form the foundation for inference. The great majority of contemporary publications in the biological sciences draw on mathematical tools. To fully appreciate the evidence underlying a scientifc statement, mathematical knowledge is required and every scientist should know a basis of statistics and programming. But don't worry: while statistics use mathematical concepts, they require a different set of logical thinking, and you don't have to be a mathematician to be a great statistician and vice versa. If mathematics is not your strongest suit, you can still get an understanding of statistics and be an excellent scientist, while for the more comprehensive studies and models, an interdisciplinary approach including statisticians, mathematical biologists or bioinformaticians is usually the way to go.

The requirements: Mathematical biologists are working in a feld that spans disciplines as diverse as mathematics, biology and bioinformatics. Bachelor's degrees in biomathematics, biology, bioinformatics, statistics, applied mathematics or physics can all be good starting points for a career. In the end you want to achieve both a good knowledge of the biological system you are studying and a thorough understanding of the mathematical toolset. During your studies you may achieve this by participating in courses of other university departments, by selecting or suggesting cross-disciplinary assignments and research projects and by working in cross-disciplinary research groups. Programming experience is an essential skill. For graduate students and postdocs, experts in specifc tools or analysis methods often offer internationally advertised courses.

Most research questions in the life sciences can only be answered in collaborative efforts. Fruitful collaborations between researchers of different disciplines require a mutual understanding of basic principles and a shared vocabulary. Mathematical biologists can be viewed as working in a continuum between mathematics and biology. You can select where to specialise on this continuum based on your personal interests and talents. If your prime interest is in developing mathematical tools, in abstraction or in exploring systems, you may choose to study theoretical physics or applied mathematics. Bioinformaticians typically focus on the analysis of data acquired in the feld of molecular biology as well as genetic and genomic data. Statisticians are trained in experimental design and the analysis of experimental data. Biologists receive an in-depth training in the methods and concepts of their discipline enabling them to identify research questions from which their discipline will proft. Efforts to acquire a good knowledge in related disciplines will be important throughout your career.

### **4 Accounts of diferent career paths**

### z **Interview with Professor Dr Ursula Siebert, Director of the Institute for Terrestrial and Aquatic Wildlife Research (ITAW), Germany**

Prof Dr Ursula Siebert is a wildlife veterinarian who specialises in marine mammals. She studied veterinary medicine at the German Justus-Liebig-University Giessen and the Ecole Vétérinaire de Nantes in France, before conducting her doctoral thesis on 'Impact of mercury pollution on cetaceans from German waters' in Brussels, Belgium and Giessen, Germany. In 2007, she fnished her habilitation in zoology at the Christian-Albrechts-University Kiel and has been the Director of the ITAW since July 2011. She is a Diplomate of the European College of Zoological Medicine (ECZM) in Wildlife Population Health and a Certifed German Veterinary Specialist in wild animals.

### *What is your main research focus?*

'In my research, I mainly focus on wildlife biology and wildlife health. I supervise terrestrial and aquatic research working groups at the institute; thus, I am involved in everything the institute conducts: health monitoring on live and dead animals, acoustics, animal counts, telemetry, wildlife diseases/ parasites and population decline investigations. To protect marine mammals in particular, it is necessary to know how they live and what effects human activities have on them. Only the interdisciplinary work of several research groups and professions (zoologists, veterinarians, chemists, physicists, statisticians, etc.) and the joint evaluation of data and information lead to insights into the status of a population or species. Over the past years, human threats to marine mammals have increased dramatically and researchers need to fnd out how the animals react to changing living conditions, form conservation management strategies, and propose protected areas. Advising politics and stakeholders is also a main part of my work'.

*How did you become a scientist working with marine mammals?*

'I was conducting a part of my veterinary studies in Nantes, France, where I lived close to the seaside and started to work on marine mammals. From that point on, I followed this path and kept educating and specialising myself in marine mammal science and pathology'.

*What does a typical day as a research institute leader look like?*

'The head of a research institute has to look after everything that happens at the institute, for example, the research projects, proposals, contracts, master and doctoral students, building and facilities, as well as everybody's safety and security. I have to keep contact with funding agencies and stake holders to inform them about the progress and outcome of our research, and recognise what type of work or project are needed next to preserve marine mammals in German waters. Because I am involved in so many different working aspects, I regularly meet with ministries, contracting authorities, working groups, national and international colleagues and potential collaborators; have to read and respond to a huge amount of emails per day; write and check scientifc papers and reports; and keep an overview of everything that is going on at the institute'.

*What was your best experience working with marine mammals?*

'The best working experience concerning marine mammals is to teach and train people in different countries about them, including preparing young scientists for future research and protection of marine mammals. To see the excitement and interest in their eyes during a lecture or a practical class is always rewarding for the hard work we are doing'.

### z **Interview with Associate Professor Magnus Wahlberg, Head of the University of Southern Denmark (SDU)'s Marine Biological Research Center in Kerteminde, Denmark**

Prof Magnus Wahlberg is originally from Sweden and studied physics and biology at the Universities of Lund and Gothenburg. He worked with fsh telemetry and sound production for the National Board of Fisheries in Sweden before starting a PhD at the University of Southern Denmark, developing acoustic localisation methods for deep-diving cetaceans, focusing on the sperm whale. As a post-doctoral researcher at Tjärnö Marine Biological Laboratory, Sweden, and Aarhus University, Denmark, he continued measurements on deepdiving cetaceans, including bottlenose whales. In 2006, he was appointed chief scientist at Fjord&Bælt, focusing on studies of harbour porpoise biosonar and hearing. He was appointed Associate Professor at SDU in 2012, and in 2015 he became Daily leader of SDU's Marine Biological Research Center in Kerteminde. His current research focuses on the hearing abilities and behaviour of marine mammals and birds.

### *What is your main research focus?*

'My main research area is underwater hearing and underwater sound production in marine animals, especially marine mammals. I studied how fsh respond to sound, how marine mammals interact with fshing gear, and also how especially porpoises fnd food by using echolocation. I work a lot with underwater sound, which means I am working very interdisciplinary. Acoustics by defnition is a topic in physics. You need physicists to understand acoustics and you also need skilled engineers to build the equipment that you need for the measurements. We often work with engineers in our research'.

*How did you become a scientist working with marine mammals?*

'I started my career studying physics, actually. Then I got interested in biology and I switched to biology. But I was mainly interested in underwater sound, how animals respond to it and how they use sound underwater. For many years, I was working on different projects related to these questions. I also had a passion for marine mammals. I worked with many different scientists on some bycatch projects, I was a whale safari guide (naturalist) and very often, I helped other colleagues with their research projects just because I thought it was fun. I never ever thought I could make a career out of this passion. But I was lucky and motivated, so one thing led to the other, until I got a job at the Swedish fshery institute working with fsh and seals. Later, I started my graduate work with toothed whales, and eventually ended up in Kerteminde and have continued my career here. For me, one thing has just led to the other very much by coincidence rather than following a planned career path. And I think especially in some scientifc felds you have to be fexible and have very many hooks out in the sea of opportunities and then you may get effcient, competent or lucky so that one of the hooks is the big catch and then that's the way you go. In my opinion, you cannot sit down and plan your life a certain way, because the next opportunity is maybe in Canada or in Australia, or in a completely different feld or with another species, you never know'.

*What does a typical day as a researcher look like?*

'There are no typical days for researchers. Every day is different, and I think you have to be very open minded and adaptable. We call it 'expect the unexpected'. You should always try to fnd out if there is something new and interesting in what you are doing; that's sort of what we are mainly focusing on. On the other hand, you have to be very meticulous, because it takes a lot of discipline to formulate good ideas for projects, plan the projects, and get funding to conduct them, and also to collect and analyse the data, and fnally writing it up for a scientifc publication.

Natural scientists are trying to fgure out the unknown, how issues are connected or how biological life systems function. Our work is trying to fnd new things. And how do you do that? Well, it's not necessarily like an 8:00 am to 4:00 pm kind of job. The days usually start more or less in the same way as they do for most people: we are starting our computer and go through our emails to see if there is an immediate problem from colleagues or students that needs our attention. But otherwise every day can be very different. Sometimes we are running experiments, we have to fx technical problems, we may have some issues that we have to solve in terms of understanding an experimental result or we go out in the feld to measure sounds from the wild and we have to either prepare feld equipment or actually go out and take the measurements. Often, we dive into our computers to analyse the data and also write up papers and reports. On top of that, we are also teaching and supervising students at different levels. Finally, we have some administrative work to do. Basically, every day looks very different'.

### *What was your best experience as a marine biologist?*

'I have many fantastic experiences from feld work with whales and seals but maybe the best one I can think about is one in the Azores, which are some beautiful Portuguese islands in the Atlantic where a lot of whales congregate. We had been out there for several weeks listening for and also tagging sperm whales from a sailing boat. During our last night, when all tags were retrieved, we had to fnish up and eventually get all the equipment back into the boat, which actually took the whole night. It was already in the early morning hours when we had everything organised. I had been able to sleep a little bit during the night whereas the rest of the crew was completely exhausted. So, I was the only one who was sort of fresh enough to sail. There I was, sitting all alone while the sun was rising, and right beneath the stunning volcanic landscape of the Azores, quietly sailing the boat back to the harbour—that was a fantastic experience!'

### z **Interview with Professor Eric Parmentier, Director of the University of Liège's Functional and Evolutive Morphology laboratory, Belgium**

Eric Parmentier is a fsh and 3D-modelling expert who graduated from the University of Liège's animal biology department before studying Carapidae, a sound producing fsh family whose members infltrate invertebrates. With the aim of carrying out comparisons, his research expanded to other fsh families capable of acoustic communication.

*What is your main research focus?*

'I like to work on different subjects. In the lab, we work mainly on the acoustic communication of fsh. We try to understand which messages fsh send, how they produce their calls and how we can use these calls to monitor the environment. If fshes are able to send sounds, they should also be able to receive them, meaning that we are also working on their hearing abilities. Additionally, we examine the feeding modes of different fsh species. Being able to feed on different prey and food items means that you are able to share the same environment and different niches. This way, we can explain the biodiversity of fsh in the same habitat. Our latest project in the lab concerns marine mammals. They have different sizes, anatomies and physiologies, and do not all live in the same parts of the ocean. Using the vertebrae of the backbone, we try to explain how they evolved and adapt to different environments. Our work slogan could be: show me your backbone and I will tell you where and how you live'.

### *How did you become a scientist working with aquatic animals?*

'I simply like to be in the sea. So, I suppose, it is easy to understand that I also like to understand how creatures of the sea are living. How they communicate, how they adapt to changing situations and how they thrive. The most obvious way to fnd answers to these questions was to study them—so I became a biologist'.

*What does a typical day as a researcher look like?*

'It depends on the day, because I am a professor and I also have to teach. However, much of my time is spent in a lab, working with bones, graphics and animations. But right now, while answering these questions, I am in Guadeloupe (in the southern Caribbean Sea) for one month with my research team and it is 6 am. In twenty minutes, we go to sea. We will probably swim four to fve hours to collect different fsh species we suspect to be vocal. Once we catch them, we place them close to the beach in shallow water and use hydrophones to record their sounds, if possible. We also take small tail samples for genetic studies. After sampling, some fsh are set free immediately, while others are kept longer for morphological studies. If the fsh is vocal, we can go back to the sea to place other hydrophones allowing us to follow the fsh's sonic activity for longer times. We can also use cameras to explain fsh behaviour through videos. This kind of feldwork is always very exciting, but can also be strenuous and exhausting work. Once we are home, we have a huge amount of data that needs to be analysed and interpreted, so when we leave the feld the work is by no means done'.

### *What was your best experience as a marine biologist?*

'There is no best experience, but a lot of nice experiences. Each time we visit a new place or we know we are the frst people to observe something, we are excited and happy. For example, during this mission in Guadeloupe, we are the frst to record and describe the sounds of ten different fsh species! Before us, nobody knew these fsh were even able to produce sounds. Isn't that amazing? It is also neat to communicate the experiments we have done and our research outcomes. The description of new fsh species was also a great thing. So, there are a lot of nice experiences in my life as a marine biologist'.

### z **Interview with Dr. Iwona Pawliczka, Head of Prof. Krzysztof Skóra Hel Marine Station, Department of Oceanography and Geography, University of Gdansk, Poland**

Dr Iwona Pawliczka studied marine biology at the University of Gdańsk. She has always been interested in marine mammals but did her master's thesis on fsh diet. During her studies she published her frst paper on harbour porpoises as a co-author of an international team. After a couple of years spent far from the sea, she got a position at Hel Marine Station University of Gdańsk where she took care of the research and population reestablishment and stabilisation of Baltic harbour porpoises and grey seals. She fnished her PhD on the biology, population status and threats to harbour porpoises in the Polish waters of the Baltic Sea. Her current research and conservation work focusses on the biology of and threats to marine mammals. She is a member of different international forums dedicated to marine mammal protection in European waters, including ASCOBANS and HELCOM expert groups.

*What is your main research focus?*

'Marine biology is a very multidisciplinary science. In our situation in Poland, where there aren't so many marine mammals, and at the same time not so many scientists working on them, it is very important to cover a lot of different issues in this kind of research. At Hel Marine Station the team and I try to cover not only biology, behaviour and monitoring—but also more specifc research as toxicology, parasitology and microbiology. We try to fnd out as much as possible about marine mammal populations that live here in the Baltic Sea. At the same time, we cooperate with a lot of different international teams like the ITAW, which are specialised in their own very specifc aspects in the lives of marine mammals'.

### *How did you become a scientist working with marine mammals?*

'From the beginning of my life, I lived at the seaside. I was pretty sure that my professional life has to be connected to the sea, in some way. Growing up, I decided, that the biology of the sea was the most exciting for me. I had the chance to observe marine life from a very young age. I became more and more excited and curious about it, asked myself how marine mammals can live in the water and what adaptations they have to live in the marine environment'.

*What does a typical day as a researcher look like?*

'I think marine biologists and researchers, in general, are independent workers. It very much depends on how you organise your work in your offce and the feld. Firstly, you have to fnd fnancial support to carry out projects. You have to fnd co-workers and research teams, often internationally, who are also interested in the same project or research questions. Writing grant and project proposals is a large part of a researcher's life. Then you have to organise your time between feldwork, offce work, conferences, workshops, and writing publications and project reports. The frst stage of almost all projects is dedicated to feldwork. Sometimes on the ocean, sometimes at the beach, sometimes in the laboratory. Being out on the ocean or working hands on with marine mammals is obviously a prize for every researcher, which is only occasionally awarded. Often, you have to spend a lot of time inside the offce or in labs. But you may also have to dedicate your time and your research to working at the university and to education, both academic and public education. It is very important to deliver the most recent data to the public, to politicians and to decision-makers, to take care of the environment and to trigger positive progress'.

### *What was your best experience as a marine biologist?*

'This is very diffcult to say. My job and being a researcher have so many facets and so many different days, and you get so many different experiences, that it is very diffcult to say which one was the best. But, I would defnitely say, that the happiest moments and days are when you can really observe the results of your work out in nature and how the animals live in their natural environment and not in captivity, not in the labs and not in the offces. So those are the best moments in my life as a marine biologist'.

### z **Interview with Dr. Andreas Ruser, Deputy Director and Head of the Bioacoustic Research Group at the ITAW, Germany**

Dr. Andreas Ruser is a trained physicist. He graduated from the Faculty of Mathematics and Natural Sciences of Kiel University in 2001. During his doctoral research in biophysics, he focused on analysing chlorophyll-fuorescence to determine marine algae groups and on investigations on natural water samples with fow cytometers. One of his interests focuses on the layout and construction of analogue and digital circuits and he is in charge of the development and improvement of different monitoring-systems (for water levels, currents, waves, underwater sound, animal hearing, etc.).

### *What is your main research focus?*

'The bulk of my work is in the feld of bioacoustics, where I mainly perform research on marine mammals. My working group focuses on underwater noise and hearing of harbour porpoises, harbour seals and grey seals, in particular on the impact of anthropogenic underwater noise. We examine the animals' ears to understand the physical effects of anthropogenic underwater sound on hearing, and also try to investigate how sound affects the distribution of animals within their habitat. To record sounds in the ocean, acoustic recording devices (hydrophones) are stationed underwater. Through their recordings, we can learn how severe the underwater sound input is and can determine its effects on marine animals. By analysing the recordings, we can detect whether animals are present in the vicinity of the hydrophones or not. In addition, we also tag animals with acoustic recording and GPS devices and later try to fgure out how an animal behaves when exposed to underwater sound. Through our bioacoustics research, we try to answer questions regarding their normal physiology, anthropogenic infuences on behavioural change and the severity of underwater noise pollution effects'.

### *How did you become a scientist working with marine mammals?*

'The career process until I started working with marine mammals was very long. I was always interested in technology and this passion led to the decision to study physics. During my studies, I would have never dreamt of ever working with marine mammals. That was never my plan. However, I always wanted to work in the feld of applied physics. Meaning no theoretical research, but something that can be measured or somehow captured and practically implemented. During my university studies, I worked in a very different area, namely in photosynthesis research. During the course of my career, I moved from basic photosynthesis research in terrestrial plants, over investigations of phytoplankton, to research on marine mammals. In fact, my research objects have slowly but steadily increased in size throughout my career. In the end, working with and on marine mammals happened just like that. I always had a natural interest in this subject, but the basis to become a marine mammal researcher was paved very early on by my fascination and orientation for applied physics'.

### *What does a typical day as a researcher look like?*

'This morning, my day started like every other workday. With a rather unpleasant sound: the repeated buzzing of my alarm clock. Like most people working at the institute, I would rather be outside in the feld watching and studying marine mammals and recording their call behaviour instead of working in the lab. The step into the acoustic laboratory is sobering; it looks like a NASA control room with banks of computers and boxes flled with equipment such as hydrophones, amplifers, cables and sound cards. A colleague is staring at the computer screens, but he is actually listening to the sounds of blue whales the team recorded in Iceland. Sound recordings come with a collection of a gigantic amount of data. Each recorded second represents, depending on the sample rate, up to more than 500,000 data points. These huge amounts of data and many hours of recordings require many cups of coffee, the use of powerful software, excellent programming skills and proper data management. The subsequent analysis of sound is diverse and requires more cups of coffee, but statistical programmes allow data organisation, calculation, statistical computing and graphic display of recorded sounds. This means, that we will sit in front of our computers for the rest of the day, analysing the collected data, trying to refne our programmes and change statistical descriptive parameters to improve our results. Often, we let the computers calculate overnight, so that we have the next dataset analysed the next morning and we can continue working on it'.

*What was your best experience as a scientist?*

'Apart from a very mind-boggling experience with different plankton types during my

doctoral chlorophyll-fuorescence research, my best experience as a scientist is the acoustic work with a harbour porpoise. Doing my frst hearing tests and auditory experiments with porpoises was my absolute career highlight. For one, the animals are extremely special, all the porpoises I've studied so far have their own personality, which is amazing and relatively unbelievable. They may not look like it, but porpoises are simply highly fascinating, remarkable animals. It is just something completely different to work with a large animal, compared to researching microscopic plankton structures that are barely visible to the naked eye. Moreover, every feld investigation is a new challenge, always extremely complicated. You have to think about and consider an incredible amount of possibilities and in the end, everything has to work in the feld. Something that is easily done in a lab is usually a challenge on site and feldwork is always complicated and often nerve-racking. Even if you have tested the entire equipment and the measuring system worked perfectly a few hours ago, the conditions in the feld are always different. Suddenly, an electronic system that was previously running fawlessly for weeks in the laboratory shuts down without a reason while you are working on a porpoise. Adrenaline kicks in and you have to fnd a fast and easy solution to the problem to still get reliable results at the end of the day. That is why a good day out on the water, where everything works and you get good results is so satisfying. When all your hard work is rewarded with aspired data, the whole team is happy, the examined porpoise is healthy, has good hearing abilities and can happily swim off—that is always a great feeling and the best motivation one can think of'.

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# **Supplementary Information**

**Glossary – 92**

### **Glossary**

**Acoustic deterrent device** A device that plays out loud sounds to make seals avoid predating on fshing gear and fsh farms. For porpoises, sounds of less intensity is used to avoid bycatch; these devices are known as *pingers*.

**Acoustics** *Science of sound*, including sound production, propagation and reception.

**Additives** Substances that are added in small quantities during plastic production to induce or enhance specifc properties.

**Alternative fshing gear** Fishing gear developed to mitigate bycatch and depredation by marine mammals.

**Anthropogenic sound** Sound caused by human activities.

**Aquaculture** Raising fsh, crustaceans, mussels or algae in controlled conditions, such as tanks and ponds, or off the coast in net pens or cages, or (for algae and mussels) on lines.

**Baleen** Long and slender structures attached to the upper jaw of baleen whales. Baleen is made of keratin, a fbrous protein also found in human hair and fngernails. While foraging, water is pushed through the baleen and captures, for example, krill or schooling fsh.

**Bioacoustics** Scientifc topic combining biology, engineering and acoustics. Bioacousticians investigate, for example, sound production and reception, how sound is used by animals to communicate, fnd food and orient themselves in their environment, and how animals react to man-made sounds.

**Bioaccumulation** Gradual build-up of chemicals or toxins in an organism. Bioaccumulation refers to the combined toxic uptake from food, water, air, etc. as a result of the substance being absorbed faster than eliminated by the organism through catabolism and excretion.

**Bioindicator** *Sentinel* species, which reveals the qualitative status of the environment and indicates a problem within the ecosystem when monitored for changes in, for example, biochemistry, physiology or behaviour.

**Biomagnifcation** Also known as *bio-amplifcation*. Biomagnifcation is the increased concentration of contaminants in organisms higher up the food chain. The contaminants are accumulated by foraging on smaller animals having assimilated contaminants at lower concentrations.

**Blubber** A layer of fat under the skin of marine mammals, serving as energy and water reservoir as well as thermal insulator, and also important for buoyancy control and streamlining the body.

**Bycatch** Incidental non-targeted catch of marine animals in fshing gear. By-caught species can be non-target fsh species as well as marine mammals, birds, turtles and invertebrates.

**Clade** A taxonomic group consisting of all organisms belonging to the evolutionary descendants of a common ancestor.

**Class** A high-level taxonomic group of organisms with a common evolutionary origin. All mammals (including whales, seals and humans) belong to the class Mammalia, and birds belong to Aves.

**DDT** An insecticide, which is not only toxic but possibly also carcinogenic to humans and animals. Abbreviation of *dichlorodiphenyltrichloroethane*.

**Drag** The resistance exerted by the water to the movement of a body.

**Echolocation** Sensing the environment by receiving returning echoes of sound pulses produced by the animal. Echolocation, also known as *biosonar*, is found in toothed whales, bats and a few species of birds.

**Environmental contaminant** Harmful chemical, biological or radiological substance that has an adverse effect on living organisms and their environment. Contaminants can be derived from human (e.g. industries, wastewater, agriculture) or natural (e.g. algae and bacteria) activities.

**Epoch** Geological time period that can be observed as a layer in rocks, caused by sediments that have turned into stone. Some scientists argue that we currently live in a newly formed epoch, called the *Anthropocene*, as traces of modern human activities, such as microplastics and pollutants, can be found in newly formed sediments.

**Family** A low taxonomic rank, right above *genus*. All dolphins (including orcas) belong to the family Delphinidae, whereas humans and great apes (e.g. chimpanzees and gorillas) belong to the family Hominidae.

**Fishing gear** Gear used to catch, for example, fsh, crustaceans and squid. Fishing gear design is adapted to the behaviour and depth of targeted species. Fishing gear can be active (e.g. trawl) or passive (e.g. trap). Some widely used types of fshing gear are traps, pots, trawls, longlines, as well as fyke, seine and gill nets.

**Fluviatile** Found in, or produced by, a river.

**Fyke net** A static fshing gear consisting of a long cylindrical or cone-shaped netting bag that is fastened to rigid rings. Fish is guided towards the entrance of a trap by *wings* or *leader nets* and have a problem fnding their way out again. Fyke nets are anchored or attached with poles to the bottom.

**Genus** Taxonomic rank right above species. The harbour seal (*Phoca vitulina*) belongs to the same genus, *Phoca*, as the spotted seal (*Phoca largha*). The only species in the human genus *Homo* is humans, *Homo sapiens*.

**Gill net** Nylon nets attached to the bottom with anchors and held up by foating lines and corks. The mesh size determines which size of fsh is most effectively caught. The fsh pass through the net with its head, but not its body, and get entangled when it tries to back off. Some gill nets stand at the bottom, whereas others are foating at the surface.

**Gyres** Enormous circular surface water currents in the ocean.

**Immunotoxicology** The study of toxicity of foreign substances and their effects on the immune system.

**Invasive species** Non-native species introduced by, for example, aquaculture or ballast water of ships.

**Macroplastics** Plastic fragments larger than 2.5 cm.

**Mesoplastics** Plastic fragments with a size of 2.5–5 cm.

**Microplastics** Plastic fragments smaller than 5 mm.

**Mitigation methods** Methods used to decrease anthropogenic stressors in the environment, usually based on the concept 'avoid, accept, reduce, control'.

**Myopia** Near-sightedness.

**Necropsy** Post-mortem examination of a dead animal; corresponding to autopsy of a human.

**Noise pollution** Adding man-made sound to the environment that may harm animals.

**Order** A grouping of organisms at a taxonomic rank lower than *class* but higher than *family*. Whales and dolphins belong to the order Cetacea, whereas seals belong to the order Carnivora. Humans, and apes and monkeys, belong to Primates.

**Otolith** Ear stone in bony fsh that functions as a sensory organ detecting gravity, balance, movement and direction to sound sources. Because otolith shape is species-specifc, it is used in dietary studies of marine piscivores.

**PCB** Toxic and carcinogenic organic chlorine compounds that were previously used as plasticizers and fame retardants for plastics. Globally banned since 2001 due to toxic properties. Abbreviation for *polychlorinated biphenyls*.

**Phylogenetic tree** Illustrating the relationships between organism as a tree, where clades are found on branches stemming from the same base.

**Pinger** Acoustic deterrent device attached to gill nets and emitting ultrasonic sounds aversive to, for example, harbour porpoises. Pingers are used to mitigate bycatch problems and are mandatory in some European gill net fsheries.

**Pollutant** A substance with harmful or toxic effects on organisms and the environment.

**POPs** Long-lasting toxic organic substances that degrade extremely slowly. Two famous examples of POPs (*Persistent Organic Pollutants*) are DDT and PCB.

**Predators** Animals killing and eating other animals.

**Recycling** The process of enabling waste products to be reused.

**Refractive index** A medium-specifc measure of the amount of bending of light rays experience when going from one medium to another. Proportional to the speed of light.

**Rete mirabile** A complex network of veins and arteries found in some marine mammals. The function is unknown but is believed to be involved in the diving response.

**Rods** Anatomical structure in the eye containing pigments that are light sensitive but cannot discriminate between colours (for colour visions, the eye uses pigments found in cones).

**Seafood certifcation schemes** Offcial certifcate organizations with the main objective to ensure that labelled fsh was caught using techniques that minimize bycatch of marine mammals or other marine organisms.

**Seal culling** Seal hunting. Seals have been harvested through thousands of years for their fur, blubber, liver and meat, as well as a pest control to reduce their competition with fsheries.

**Soundscape** The entire amount of sound in a certain location, usually added together by many different sound sources (both natural and man-made). The term is the acoustic analogue to the visual *landscape*.

**Steroid hormones** The term 'steroid' indicates certain hormones synthesized in the gonads (sex steroids) and adrenal glands (corticosteroids). Steroid hormones control metabolism, immune functions, infammation and development of sexual characteristics.

**Taxonomy** The science of classifcation of animals and plants according to how closely they are related. The corresponding adjective is *taxonomic*.

**Toxins** Poisonous substances (molecules, peptides or proteins) produced within living cells or organisms. Toxins can cause disease on contact with or absorption by body tissues.

**Trace elements** Previously called *heavy metals*, trace elements are trace dietary components essential in minute quantities for the proper function of the organism. Examples are cobalt, copper, fuorine, iodine, iron, manganese and zinc. Trace elements may be toxic at high concentrations, and some are toxic even at lower concentrations.

**Trawling** Fishing by towing a trawl (a coneshaped net ending in a bag) with one or more boats. Some trawls are made to be towed long the sea foor (bottom trawl) and others at middepth (pelagic trawl).

**Viviparity** Live birth (as opposed to, for example, birds laying eggs).

**Wave propagation** The physical description of how a wave (e.g. an acoustic signal) travels from one location to the other. The wave changes while traveling with respect to its amplitude, duration and frequency content.

**Whaling** Hunting whales, dolphins or porpoises. Whaling has been going on for thousands of years. In the nineteenth century, whales were mostly hunted for their blubber and baleen. Industrial whaling of the twentieth century, mainly for meat, brought many large whale species to near extinction.