THE INCONGRUITY OF THE BLUE WHALE (Balaenoptera musculus) is that it may be the world’s largest animal but it survives on a diet of one of the world’s smallest animals – shrimp-like krill. (To be perfectly accurate, there are lots of things smaller than krill, but, really, krill are little. Shrimp-like. Usually less than an inch long. You get the idea).
THE BALEEN FACTOR Blues, of course, are baleen whales – rather than having teeth their mouths are equipped with baleen, a filtering structure similar to bristles made of keratin, a substance found in fingernails and hair. When a baleen whale opens its mouth underwater, the water pours in. Pushing the water out traps tiny animals like krill in the baleen. It’s the Big Guys’ principal source of nutrition. Blue whales do this by going where the krill are, often hundreds of feet deep in dives that last up to 15 minutes.
How does B. musculus, which can be more than 100 feet long and weigh more than 330,000 pounds, survive on a diet of tiny crustaceans? Very well, actually. Krill may be small but they swarm in enormous numbers, so sweeping through a shoal of them can net a lot of tasty little crustaceans.
WHY NOT LONGER DIVES? The question that intrigued the University of British Columbia research team led by zoologist Robert Shadwick was why blue whales’ dives were so short considering the massive oxygen supplies available to them in their enormous volumes of blood and muscle, according to a report on their research in the Journal of Experimental Biology. Wouldn’t whale foraging, they wondered, be most productive with longer dives?
Based on the whales’ technique of inflating their mouths somewhat like parachutes to capture prey, the team studied parachute aerodynamics to define the forces acting on whales as a they dived, and they built mathematical models to calculate the amount of energy the whales expend on dives. They measured museum-based blue whale jawbones and calculated the density of krill swarms a whale might encounter on a dive.
They found that the volume of krill a blue whale harvested on a single forging dive could provide as much as 90 times the amount of energy it expended making the dive. Specific lunges could return as much as 240 times nutritional energy as energy expended.
SUCCESSFUL HUNTER/GATHERERS – OF KRILL Whales, they found, are remarkably productive in foraging just the way they do it.
Assuming they like krill.
(Another To Be Accurate note: Northern Atlantic blue whales can be more than 100 feet in length. The animals that were studied were northern Pacific blue whales, which tend to be smaller than Atlantic blue whales – more like a mere 88 feet in length. But the principle remains).
Principal Source: “Blue Whale-sized Mouthfuls Make Foraging Super Efficient, Kathryn Knight, Journal of Experimental Biology, January 1, 2011; National Oceanic and Atmospheric Administration.