In this insight, Dr. Ari Friedlaender, Associate Researcher at University of California, Santa Cruz discusses his latest publication in Functional Ecology “The advantages of diving deep: fin whales quadruple their energy intake when targeting deep krill patches”, and more broadly discusses his research interests and path to becoming an ecologist.
About the paper
What’s your paper about?
Our paper is about the feeding behaviour of one of the largest animals on the planet, the fin whale, and how these whales maximize their energetic gains. We used dive recording tags deployed around the world and measurements of the vertical structure of their prey to show that fin whales increase their feeding rates when diving deep. This is important because as air-breathing animals that have to return to the surface regularly, if you are going to make the effort to dive deep you should maximize your time at depth feeding rather than use the majority of your time transiting back and forth to the surface. Coupled with information that prey density is higher at depth, we were able to calculate that fin whales actually consume 4 times more prey at depth versus when they feed on shallow dives and on prey that is less dense. The take-home message is really about how the largest animals on the planet are able to maximize their energetic gains by modifying their behaviour to augment feeding opportunities based on the availability of prey.
What is the background behind your paper?
Air-breathing diving animals (marine mammals, seabirds, etc) face the dual challenge of having to dive to find food in marine /aquatic systems and balancing the need for oxygen. Understanding how different animals have evolved physiological, morphological, and behavioural adaptations to be successful in these environments is of great interest. Baleen whales are some of the largest animals that have ever lived on the planet. They have enormous energetic demands and have also evolved a bulk filter-feeding strategy that allows them to engulf vast amounts of prey-laden water at one time. This is a very costly feeding strategy though so baleen whales must balance the costs of this activity with the gains from foraging on patchy and heterogeneous prey. Very little information exists on fin whales, the second largest animal on the planet, and our goal was to study the ecological relationship between fin whales and their prey to understand how these animals survive and thrive in marine ecosystems.
What are the key messages of your article?
I believe that the key messages of our work relate to understanding how air-breathing diving predators have evolved really remarkable strategies to take advantage of prey to both satisfy their energetic demands and maximize energetic gains in an extremely difficult environment for air-breathing animals to survive. That fin whales are able to quadruple their energetic gains when foraging on deep and dense prey patches is a remarkable piece of information that supports our and other work showing that diving animals increase their feeding rates when diving to greater depths in an effort to maximize feeding time.
How is your paper new or different from other work in this area?
Our work is novel and unique as it is the first such study of the ecological relationships between fin whales and their prey in a quantitative way where both predator behaviour and prey availability were measured concurrently. Similar work has been done on blue and humpback whales, but this is the first work of its kind on fin whales.
Understanding how fin whales maximize their energetic gains raises new questions about how these relationships scale with body size among air-diving predators.
Does this article raise any new research questions?
Absolutely! Baleen whales as a group span a range of body sizes, energetic needs/demands, and foraging strategies. Understanding how fin whales maximize their energetic gains raises new questions about how these relationships scale with body size among air-diving predators. This work also raises questions that relate to the impacts of human activities including anthropogenic noise in the ocean. For example, it has been shown that blue whales respond to navy sonar by cessation of feeding specifically on deep foraging dives. For blue whales, deep feeding on dense prey is the only measured foraging strategy in which blue whales actually gain energy. Given their large body size, the same may be true for fin whales. Our data show that fin whales maximize their feeding rates and energy intake when feeding on deep and dense prey and this makes them extremely vulnerable to disturbance if in fact they respond similarly to their close relative, the blue whale.
Who should read your paper?
I believe this paper is of interest to behavioural ecologists and those who are studying predator-prey interactions, and how these manifest in different environments and land/seascapes. I also believe that this work is of interest to comparative ecologists seeking to understand how the evolution of different foraging strategies have evolved over time. This work is also important for policy makers and those interested in developing methods and strategies to tests for behavioural responses of marine mammals to anthrpogenic sound in the ocean.
About the research
What is the broader impact of your paper?
Baleen whales are at the extreme of body size and foraging strategies, our work provides new information on how the largest animals on the planet are able to find and exploit patchy prey effectively.
Why is it important?
This work is important because fin whales represent some of nature’s maximums in terms of how large and efficient animals can be and the extraordinary ways in which evolution has worked to develop amazing ways to be successful in an otherwise inhospitable environment for air-breathing animals. It is also important because it provides the knowledge that fin whales, like blue whales, may be at extreme risk from human disturbance via ocean noise.
Did you have any problems setting up the experiment/gathering your data?
Fin whales are incredibly difficult to study and in order to achieve the sample size necessary to support our conclusions, great efforts were required by a large number of researchers around the world for several years.
What would you like to do next?
I would like to conduct similar experiments and collect data from other closely related species of baleen whales to truly test how differences in body size, environment, prey, and energetic demands affects how these ocean predators behave.
About the Author
How did you get involved in ecology?
As soon as I started my academic training to understand how animals are adapted for life in marine ecosystems I was interested in how this manifested to relationships between animals and their environments. Initially, I studied why bottlenose dolphins were becoming entangled in gillnets in coastal North Carolina. This required understanding why the dolphins were there and what drove their behaviour. During my dissertation work in the Antarctic, I then studied how the distribution of baleen whales was related to and affected by environmental conditions in the most extreme but productive ecosystem in the world. This further peaked my interest to delve into the behaviour of individual animals to better understand the decisions these ocean predators made and how the environment in which they live affect them.
What are you currently working on?
Similar work with minke whales, the smallest baleen whales in the world. Understanding the ecological relationships between baleen whales will offer great insights as to how differences in body size and energetic demands affect behaviour, foraging strategies, and the ecological needs of different species.
What’s your current position?
What is the best thing about being an ecologist?
Being able to do multi-disciplinary research with colleagues and scientists and students from different backgrounds and interests. Being an ecologist, to me, requires being in the field, learning about an environment and the animals in that system, and working with people to better understand the connections between animals and their environment.
One piece of advice for someone in your field…
Always keep your eyes open, always push the boundaries of what you think you know, and never stop being curious.