Ever wonder how baleen whales (Mysticeta) get enough to eat? The mechanism is described for rorqual whales (Balaenopteridae) in a review article published this past October in Physiology.
Researchers have found that rorqual whales (ex: blue whales and fin whales), in particular, have an interesting strategy for foraging. The process includes 5 steps that take place in rapid succession (about 20-90 sec total): quick forward lunges toward prey; opening their jaw up to 80 degrees; ingesting large amounts of water containing prey (up to 150,000 liters for a 28 meter blue whale); closing the mouth and filtering out excess water; and finally, swallowing their prey. The whales are able to open their mouths wide thanks to having grooves that are packed with stretchy elastin fibers.
The ability to lunge such a large body forward sounds like a process that would require a lot of energy. In fact, the animals can lunge forward multiple times at speeds up to 3-6 meters/second before surfacing for air. Surprisingly, researchers found that the energy required to lunge favors larger whales as they can ingest more water containing prey than smaller whales.
This video posted to YouTube shows a blue whale foraging on a large mass of krill:
Shadwick R, Potvin J, Goldbogen JA. Lunge Feeding in Rorqual Whales. Physiology. 43(6): 2019. https://doi.org/10.1152/physiol.00010.2019