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Field Notes

Covering the natural wonders of the Pacific Northwest

March 8, 2013 at 7:00 AM

Open wide: Feeding the largest animal on Earth

One of the mysteries of the natural world is why and how the biggest animal alive, the blue whale, manages to feed itself on a diet of such tiny prey: krill. The tiny crustaceans are no bigger than a paper clip, yet they constitute the diet of many whales, including blue whales, fin whales, humpbacks and minkes that feed off Washington’s Coast.

To figure out how they do it, Jeremy Goldbogen, of the Cascadia Research Collective in Olympia, and his colleagues figured out how to tag swimming blue whales with a stick-on camera when they surface. Not so easy to do, by the way, on an animal bigger than a school bus. Using a long rod and adhesive to smack the camera on the surfacing whale’s back, they were able to ride along with the whale to see how it feeds. (The camera falls off in a few days, and has a transmitter on it to enable scientists to retrieve it, floating in the water.)

Here’s more on the tagging operation from Science Magazine.

From the footage, Goldbogen and his colleagues learned that the blue whale and others in the so-called rorqual family have highly specialized biomechanics to pull off a feeding method unique in the animal kingdom. Goldbogen presented his findings recently at the annual meeting of the American Association for the Advancement of Science in Boston. The whales lunge feed, accelerating as they swim through the water to drill through aggregations of krill.

And the blue whale is perfectly built for the task. Its  large body enables it to feed efficiently on the pastures of the sea, opening a specially adapted mouth to capture some 80,000 gallons of water — a volume heavier than its own weight — in just a few seconds. In repeated lunges over several hours, the animal can ingest more than a ton of krill, plenty of food for the entire day.

To do it, the whale accelerates to top speed and opens its mouth 90 degrees — special hinges in its jaw allow this big gulp — forcing the water into its oral cavity. The mouth and jaw area — which is unusually large, taking up more than 25 percent of the body area — works in concert with blubber pleated like a bellows to allow the whale to blimp out from its mouth to its vent, up to four times its resting size.

As if that weren’t enough, its tongue also is specially adapted to unfurl and invert to form a wall at the back of its throat and push back into the whale’s body cavity all the way down to its belly button, to ingest the massive amount of water it captures in its lunge. Then it pushes the tongue forward, to press the krill through baleen plates of keratin (the same substance in hair and fingernails.) Water out, krill in, dinner is served.

How the blue whale feeds. Graphic courtesy of Jeffrey Goldbogen

How the blue whale feeds. Graphic courtesy of Jeremy Goldbogen

 

Much of that mechanism was already known from work by earlier researchers. But the coup de grace for Goldbogen and his colleagues was the camera. When they stuck it on swimming blue whales they discovered the whales barrel roll as they lunge through krill, mouths agape. The roll enables them to ambush their prey, as they blast through a krill patch at 16 feet per second.

All in a day’s work for whales, mammals so unique in their kingdom that “it is as if they are dropped from space,” Goldbogen said. “There is nothing else like them.” True, they suckle their young on milk, and have a few residual hairs if you know where to find them. “But they look much more reptilian or snakelike.”

The blue whales’ many extreme adaptations enable them to get a lot of food efficiently. Much more so than captures of individual fish. Goldbogen is still trying to figure out which came first though: the animals’ gigantic body size, or their unique feeding mechanism.

Here’s a link to National Geographic’s Science Friday with some amazing footage from the so-called Crittercam.

Comments | Topics: blue whale, Jeremy Goldbogen

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