ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Mathilde Chevallay is an author on ‘ Sealing the deal – Antarctic fur seals’ hunting tactics to capture small evasive prey revealed by miniature sonar tags’, published in JEB. Mathilde is a PhD student in the lab of Christophe Guinet and Tiphaine Jeanniard du Dot at Centre d'Etudes Biologiques de Chizé, France, investigating fine-scale predator–prey interactions in diving predators of the Southern Ocean using state-of-the-art biologging devices.

Mathilde Chevallay

How did you become interested in biology?

Since my childhood, I have been very curious about how and why animals behave the way they do. In particular, I have always been fascinated about how animals sense and perceive their environment, and how they use the information they obtain from their environment to move through space, to find their food, to avoid predators and to make decisions that allow them to survive in their complex environments. I remember spending hours following my cat around the garden with a notebook to record his behaviour. He was not a good hunter, but I loved watching him explore his environment, choosing his ‘prey’ and figuring out, or at least trying to figure out, how to catch them. Marine animals particularly intrigued me because, unlike my cat, you cannot just follow them and observe them directly, and I really wanted to know what they do when they are in the deep ocean! When I was doing my bachelor’s degree, I met Christophe Guinet, one of my PhD supervisors, who specialised in the foraging behaviour of deep-diving predators of the Southern Ocean, and his research was perfectly in tune with what interested me: understanding how predators find and capture their prey in the deep ocean. This is where it all started.

Describe your scientific journey and your current research focus

I studied marine biology at Brest University (France) for 5 years (bachelor’s and master’s degree). During my master’s, I did two research internships in the Centre d'Etudes Biologiques de Chizé, where I specialised in the study of the foraging behaviour of diving predators, especially pinnipeds such as fur seals and elephant seals. Following my master’s internships, I started my PhD in 2021 on fine-scale predator–prey interactions in diving predators of the Southern Ocean, i.e. elephant seals, fur seals and king penguins. To do so, I used an innovative approach called biologging, which consists of deploying devices on animals to record detailed information on their behaviour and their environment in areas that are normally totally inaccessible to us. Thanks to these recording devices, we can now have access to a whole new range of information on the life at sea of these mysterious and charismatic deep-diving predators. In particular, the aim of my PhD is to better understand how these deep-diving predators detect, select and capture their prey in the deep and unlit waters of the Southern Ocean, and to study the impact of environmental parameters on the distribution and behaviour of their prey, in order to better anticipate the effects of climate change, which is particularly intense in the polar areas, on the ability of these predators to efficiently find and capture their prey.

How would you explain the main findings of your paper to a member of the public?

The aim of this research was to study the hunting tactics of the Antarctic fur seal, a small marine mammal, and to compare them with the ones of the largest seal, the southern elephant seal. These two seal species both live on the same sub-Antarctic islands and forage on the same type of prey: small lanternfish. However, they are very different in terms of morphology, diving capacity and locomotor performance, so they probably will not hunt their prey in the same way. On the one hand, you have the southern elephant seal, the largest pinniped weighing several hundred kilograms, a very good diver but quite slow and not very manoeuvrable; and on the other hand, you have the small Antarctic fur seal, a poor diver, but very manoeuvrable and able to perform fast accelerations. Therefore, our aim was to better understand how these predators can efficiently exploit the same kind of prey, being very different.

To answer this question, we deployed on these two species an innovative biologging device, the sonar tag, that combines movement sensors (the same types of sensors found in connected watches, for example), allowing us to describe the fine-scale behaviour of predators, with a small sonar, which can scan every prey encountered by the predator during their hunting periods and give us precious information on their prey characteristics and behaviour.

We showed that fur seals and their prey detect each other at the same time, i.e. 1–2 s before the strike, forcing fur seals to display reactive fast-moving chases to capture their prey. In contrast, elephant seals detect their prey up to 10 s before the strike, allowing them to approach their prey stealthily without triggering an escape reaction. Therefore, we show that our two very different predators rely on distinct hunting strategies according to their locomotor performance, manoeuvrability and sensory capacities, allowing us to better understand how they can efficiently capture the same kind of prey.

A female Antarctic fur seal equipped with a miniature sonar tag in the Kerguelen Islands.

A female Antarctic fur seal equipped with a miniature sonar tag in the Kerguelen Islands.

What do you enjoy most about research, and why?

I love the fact that you learn new stuff every day. It never gets boring! I work on fascinating animals in a field where there is still much to discover and each new result opens up new questions. I like the fact that it is also very diversified and that each day is different. My favourite part is writing (I know, this is the part that students usually don't like…), especially when you finally have all your results and you can start to put everything together to build your global story.

What is the most important piece of equipment for your research, what does it do and what question did it help you address?

The most important piece of equipment for my research is definitely the sonar tag. The sonar tag is a new recording device that can be deployed on several species of marine animals (seals, sharks, penguins). It is like a connected watch that records almost all the life of our animals, from their location to their dives and all their movements with super precision (up to 200 pieces of information per second!). It also integrates a small sonar that, similar to the ones usually found in ships, can scan every object and organism that our animals encounter during their dives, and can give us very detailed information on these organisms, such as their size, gregarious behaviour or escape behaviour. Therefore, thanks to this tag, we can describe very accurately every detail of the life of our animals! I use the data recorded by this tag to describe the fine-scale predator–prey interactions in diving predators of the Southern Ocean (seals and penguins) that are usually poorly studied because of their inaccessibility during their hunting periods.

Do you have a top tip for others just starting out at your career stage?

For me, the most important thing is to surround yourself with caring people and to work in a healthy environment. I have the chance to be supervised by two incredible supervisors, who have always been very attentive and caring, and I am convinced that it really allowed me to fully enjoy my PhD. For me, having a good supervisor is at least as important, if not more so, than having a good PhD subject. I would really recommend that people who want to embark on a PhD choose their supervisors carefully, meet them, talk to former students, and check that there is a good working relationship before taking the plunge. And then, enjoy!

What's next for you?

I am in the middle of my last year of my PhD so I have completed most of the analyses I wanted to do during my thesis and I am starting to write my dissertation. I really enjoyed doing my PhD, and I really want to continue a career in research. I am now thinking about what I want to do next and what aspects of research I want to explore. The results obtained during my thesis open up a whole range of questions that I would like to explore in more detail. In particular, I would like to study the inter-individual differences that can be observed within animal populations. The way in which these differences between individuals emerge within a population, why they emerge, how they are maintained and transmitted and how they will impact on the survival of individuals, their ability to reproduce and therefore population dynamics in the longer term are questions that I am particularly interested in and that I hope to address in my future research projects.

Mathilde Chevallay’s contact details: Centre d'Etudes Biologiques de Chizé, Centre National de la Recherche Scientifique, 79360 Villiers-en-Bois, France.

E-mail: [email protected]

Jeanniard du Dot
Sealing the deal – Antarctic fur seals’ hunting tactics to capture small evasive prey revealed by miniature sonar tags
J. Exp. Biol.