How do big whales manage to put enough tiny bits of food in their bodies to get to such huge sizes?
For example, a fin whale will dive hundreds of feet down in search of food. Once it gets deep enough, it speeds up dramatically, and then abruptly slows down, almost stopping. Yet even as it slows, its tail is still moving up and down, generating tremendous thrust. Then, about half a minute later, it speeds up and slows down again. What’s going on?According to the scientists, this pattern occurs when the whales lunge into a cloud of krill and drop open their jaws. Pleats under the lower jaw open up, engulfing huge amounts of water. The whale slows down because of the drag. It behaves, in other words, a lot like a parachute.
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It’s a lot of water, the scientists have found: in one lunge, a fin whale can momentarily double its weight.If a whale simply let the water come rushing in, there would be a tremendous collision — more than a whale could handle. Instead, the scientists argue, the whales actively cradle their titanic gulp. As the water rushes in, the whales contract muscles in their lower jaw. The water slows down and then reverses direction, so that it’s moving with the whale. (It just so happens that fin whales do have sheets of muscle and pressure-sensinging nerve endings in their lower jaw. Before now, nobody quite knew before what they were for.) Once the water is moving forward inside the whale it can then close its mouth and give an extra squeeze to filter the water through its baleen.
This bizarre strategy may be the secret to the huge size of some whales. A fin whale can get 20 pounds of krill in a single gulp, but it can gulp every 30 seconds. Because krill live in gigantic swarms, they can keep gulping and get enough food in four hours to fuel their bodies for an entire day.
Big fin whales are not just scaled-up versions of little fin whales:
Instead, as their bodies get bigger, their mouths get much bigger. Small fin whales can swallow up about 90% of their own body weight. Very big ones can gulp 160%. In other words, big fin whales need more and more energy to handle the bigger slugs of water they gulp. As their body increases in size, the energy their bodies demand rises faster than the extra energy they can get from their food.