Julie Marie van der Hoop has just finished up a Marie Sklodowska-Curie Postdoctoral Research Fellowship with the Marine Bioacoustics Lab at Aarhus University. In this Insight, she talks about her work on Foraging rates of ram-filtering North Atlantic right whales. In this paper, the authors used multi-sensor bio-logging tags to ask the questions: How much prey-laden water is filtered by right whales over the course of a dive, and what information do they use, as breath-hold divers, to decide to forage or not?

 How is your paper different from other work in this area?

Assumptions are natural in science, especially in modelling aspects that are challenging to measure. As new methods and technologies develop, though, we can take a step back and think – “hey, do we actually need to assume X now?” We realized that we could really refine estimates of foraging capacity by estimating the filtration speed of whales, via on-board tags, and by considering the difference in mouth size with age, with considerable effects compared to previous assumptions.

We also looked across taxa, comparing differences in mouth gapes, baleen lengths, swimming speeds, and ultimately filtration rates of different ram-filter feeders. We hope to spark some interesting discussions on comparative morphology across marine species, given the great work that is being done on ram-feeding fishes and sharks.

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Did you have any problems setting up the experiment?

We took a new look at some existing data in our tag library, as sensor analysis and inference for testing hypotheses related to foraging have really progressed since the data had been first collected. Resurrecting older data files and types, and re-organizing some of the metadata (on paper data sheets!) from almost 15-20 years ago was a bit of a challenge, but was also important to bring those data into the digital age for future use. It really put an interesting perspective on the utility of existing data, and how to bring past archiving practices up to current standards.  

How does this fit into your previous work

I previously worked on questions of drag – the resistive forces that animals experience – but more in the context of drag from when animals become entangled in fishing gear, or when scientists put tags on animals to study them. These objects increase the drag on a swimming animal, which impacts energetics and biomechanics. Some animals also feed in a way that creates a lot of drag. Ram filter-feeding whales and fishes swim with their mouths open; that large frontal area requires more thrust and energy to move forward in the water. So, what were the drag trade-offs of this foraging strategy? Tag data from North Atlantic right whales, which provided biomechanics, diving behaviour, and estimates of speed, seemed like a great opportunity to ask some of those research questions.

Much of my previous work quantified energy expenditure from fishing-gear drag on North Atlantic right whales. That work was especially rewarding in the context of the species’ critically low population and low reproduction due to entanglement. This current paper [in Functional Ecology] continues with similar principles of energetics and drag, but is more based on how these whales acquire energy over their short foraging seasons, and how they trade off the costs vs. gains of their high-drag feeding strategy.  It’s an additional piece in the puzzle of energy

What do you do in your spare time?

It’s hard to ignore some of my research topics when I’m out doing what I love – cycling. Particularly in Denmark (where I completed this research, the wind really increases the resistance (drag). When that happens, I can either slow down or increase my power output; the same principles hold for whales. While the similarities are interesting, the sport still provides an escape and a balancing force to my working life.

Read “Foraging rates of ram-filtering North Atlantic right whales” here or the plain language summary here.