Whales with different methods of filtering

Fin whales consume larger and more mobile prey: krill and small fish. “When they locate a school of krill or small fish, they accelerate, open their mouths, engulf and then close their mouths and use the powerful muscles of their belly to push the water out through their baleen,” continues Mr. Potvin. Thanks to ventral grooves that can expand like an accordion, rorquals are able to engulf a volume of water that exceeds the volume of their body. During filtration, enormous pressure is generated and the rate of filtration (the speed of water passing through the baleen) is about 10 times higher than in balaenids.

“In rorquals, baleen are short because of how fast the animals are swimming when capturing their prey. Short baleen minimizes drag and energy, and is able to withstand enormous pressure with minimal damage. Balaenids, on the other hand, catch their prey very slowly, such that they are able to expose longer baleen without generating a large drag force,” explains the physicist.

Two of the species studied – sei whales and pygmy whales – have intermediate-sized baleen that does not fall into either of the aforementioned categories. These two species likely have a less specialized diet (including small and large prey), allowing them to adapt to different ecosystems and situations, but possibly limiting their effectiveness.

The next challenge for researchers will be to compare the energy used by different whale species to feed, and to shed light on the link between their body size and the energy efficiency of their diet. Additionally, researchers will compare the energy expenditures of the bowhead whale and the blue whale – two species that feed exclusively on plankton – to understand why the blue whale is about twice as long as the bowhead.