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As a kid I had the hardest time understanding how a whale’s baleen works when reading about it in my elementary school texts. The books described these structures as working like strainers, filtering out the plankton these giant creatures feed on. I just couldn’t figure out how if these filters screened out the food as it entered the mouth it could possibly make its way to the animal’s stomach.

It finally became clear to me that the baleen didn’t filter the food as water entered the mouth, but as it left.

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(Image from Wikipedia)

Whales (Cetaceans) are divided into two groups: The toothed whales, such as orcas and sperm whales, and the baleen whales, which make up the majority of large whale species including humpbacks, finbacks and blues. Instead of having teeth like most mammals do, baleen whales have a series of comb-like structures that hang down from the top jaws like a curtain.

Baleen is made of keratin, the same compound that makes up our fingernails. The entire top jaw of these whales contain bands of hard but flexible plates that may, in a blue whale’s case, be up to six feet in length. Each baleen plate is thick and rigid at the gumline and thins out and frays near its tip, forming an interlocking mat of hair-like structures covering the mouth opening.

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(Image from NOAA)

One common misconception is that whales feed on tiny plankton. In general this is not the case. Most baleen whales feed on macro-animals such as krill and schools of fish. One exception is the right whale, which has a particularly fine baleen mesh that is capable of filtering out micro-animals such as copepods and other small planktonic creatures. This species’ name comes from its especially buoyant blubber which causes a dead one to float to the surface, making it the "right" whale for harpooners to hunt since it was less likely to be lost after the kill. This species is also unusually slow and docile, allowing the harpoon boat to easily approach the animal. Needless to say, right whales were among the first whale species to nearly become extinct from overharvesting. Even though killing Right Whales was banned as early as the late 1930’s, only about 600 individuals are alive today.

The feeding method of baleen whales, once you understand how the process works, is very simple. When a whale identifies a large food source, be it a school of fish or a swarm of krill, it opens its mouth and swims through the school, filling its mouth with water and food. As the mouth closes the tongue presses up against the roof of the mouth, forcing the water out and whatever food it contained is trapped by the inside of the baleen mesh. Once the water is ejected the food is swallowed. Lather, rinse, repeat. Over and over again, since a large whale may need to consume up to 6,000 pounds of food a day just to maintain its body weight.

In order to maximize the volume of water a whale can gulp at one time, the throat has a series of horizontal ridges that can expand like a pelican’s lower beak.

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Here you can see the throat ridges of a
humpback swelling with water and food.

There is no doubt that whales are intelligent animals, and the humpback is perhaps the smartest of them all. The complexity of their songs (listen to one here, courtesy of Cornell Ornithology Labs) indicates advanced communication skills. Some colonies have also learned to hunt cooperatively, working together to trap schools of fish in a fantastic behavior known as bubble-netting.

When a pod of humpbacks find a large concentration of fish they all dive down beneath the school. One whale will swim in a circle blowing air bubbles. As the bubbles rise to the surface they create a net that the fish won’t swim through. As a defense, the school will form a tight ball within the center of the "net" and then all the whales will rise straight up to the surface and feed on the trapped prey. Up to two dozen whales may work together to feed this way and because the designated "bubble-blower" is the last to rise, this individual usually gets a smaller share of the food. Humpbacks take turns creating the net to balance this out.

Here’s some amazing video of humpback whales bubble-net feeding on a school of herring. You can see the baleen hanging down from the smaller upper jaw and the water being released out of the sides of the mouth as the jaws close (you can see this very clearly in the last few seconds of that clip). [Update: That site's videos are having trouble. I'll keep the link up since it is the best I've found, but here's an alternative. See the second video down.]

The market force that drove commercial whaling in the past two hundred years was the demand for not only oil for lamps, but also this baleen. It was known as "whalebone" and products that bore this term were made out of baleen, not actual bone. Prior to the invention of plastics whalebone was used in corsets, umbrellas, hairbushes and other items that required strong but flexible materials. While many indigenous cultures have hunted whales for food for thousands of years, the discovery of oil made most commercial operations obsolete. Few countries now kill whales for food with the exceptions of Japan and Norway, which hunt mainly minke whales, and dishes can still be found in some restaurants.

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Minke meat served in Japan.

Fun Fact: All baleen whales have two blowholes, while all toothed whales have only one.

Other diaries in this series can be found here.

Originally posted to Mark H on Fri Mar 30, 2007 at 03:59 PM PDT.

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