Krill buildup could slow fin whale filter-feeding unless baleen stays 15% clear
Usually there's safety in numbers, but it doesn't always work that way. Fin whales (Balaenoptera physalus) filter-feed on immense shoals of krill, engulfing colossal mouthfuls of water containing up to 144 kg of the crustaceans. But then the mighty creatures expel the water by squeezing it out through the racks of baleen lining their mouths.
Extraordinarily, hungry fin whales can expel the water in 31 seconds, but Ingrid Ackermann from Stanford University was puzzled. She explains that 144 kg of krill would form a layer 6.3 centimeters (2.5 inches) deep when spread evenly across the 2.9 m2 area of baleen, potentially clogging the gigantic strainer. So how much of an impact might this clogging have on how fast the whales can eject water?
Ackermann and her colleagues, David Cade, Jeremy Goldbogen and Mark Denny from Stanford University, publish in Journal of Experimental Biology that krill could pose a serious clogging problem for filter-feeding fin whales, slowing water leaving their mouths to a 0.02 m/s dribble unless they can prevent the krill from accumulating on the baleen by maintaining a 15% window clear or keeping the krill afloat in their mouths. Then the whales can expel the water in 31 seconds to keep diving for dinner.
How the mouth empties
"When fin whales lunge, their lower jaw hinges open and water floods into a pouch stretching from their lower jaw to their belly button," says Ackermann. The team started by calculating that the view from the side of a 20-meter-long (66-foot-long) fin whale's pouch would expand from 30.5 m2 to 79.2 m2 as it engulfed a 60 m3 mouthful of water.
Then they calculated the pressures exerted as the recoiling blubber and muscle in the pouch squeeze the water out through the baleen strainer, determining pressures ranging from 4.1 kPa up to almost 18 kPa—the equivalent of a 1.8-kilogram (4-pound) weight pressing on a 10-centimeter-square (1.6-inch-square) area. These pressures could empty the whale's mouth in just 31 seconds.
But how much of a difference would a layer of krill make to the whale's ability to expel water?
Krill turns flow to a dribble
Fortunately, krill are a popular food in the pet trade, so Ackermann purchased a bag of the frozen crustaceans from a local pet store. Gently packing the bottom of a 1.6-meter-tall (5.2-foot-tall) tube with layers of krill—ranging from 1.9 to 5.6 centimeters (0.7 to 2.2 inches) deep—and filling the tube with water, the team was able to exert pressures from 8.9 to 12.4 kPa, tracking the speed of the water as it flowed through the krill. They then scaled up the speeds for the size and pressure produced by a full-sized whale.
Instead of flowing through the krill at 0.67 m/s—the speed needed for the whale to empty its mouth in 31 seconds—the water speeds plummeted to a sluggish 0.04 m/s through the 1.9-centimeter (0.7-inch) layer of krill, dribbling at just 0.02 m/s when the plug was 5.6 centimeters (2.2 inches) thick.
At those rates, it would take the whale 16 minutes to empty its mouth, which is twice as long as an average feeding dive.
"The krill might really be a problem," says Ackermann. So how might the whales get around the issue?
Clear patches may be enough
This time, the team investigated what would happen if the krill were spread unevenly across the baleen, leaving relatively unclogged windows that water could gush through.
They calculated that a whale could empty its mouth in 31 seconds if 15% of its baleen is kept almost completely clear, or the animals somehow keep the krill suspended in the water in their mouths to keep the baleen from clogging.
So it is possible for fin whales to empty their mouths fast if they can reduce krill buildup against the baleen.
How fin whales do this in practice remains a mystery, but preventing the baleen from clogging is essential for a fin whale to empty its mouth fast so that it can continue dining on clouds of krill.
Publication details
Ackermann, I. A., et al. Constraints on lunge feeding: krill can clog the baleen of filter-feeding whales, Journal of Experimental Biology (2026). DOI: 10.1242/jeb.251852
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Citation: Krill buildup could slow fin whale filter-feeding unless baleen stays 15% clear (2026, July 9) retrieved 12 July 2026 from https://phys.org/news/2026-07-krill-buildup-fin-whale-filter.html
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