The baleen plate is a strainer that enables maximum feeding capacity, which is essential for such huge animals that require so much food to satisfy their energy needs. Baleen is a horny form of whalebone, with each bristle (or horny outcrop) measuring an average of less than one-fifth of an inch (or about five millimetres) in size. The plates are curved backwards slightly, giving them tautness and solidity, and offering less resistance for the water that has to flow in and out of the mouth freely.
The outer edge of the baleen plates is rather straight, while the inner edge is more rounded. The top of the plate (attached to the gums of the upper jaw) is broad. At the bottom, where the plates taper to a point, they are far narrower. The inner edge of the plate is coarser than its outer edge.
The thickness of the hairs or bristles on the baleen plates varies from one whale species to another. Similarly, the physical size of the plates also depends much on the species. The baleen plates of the Greenland Right Whale are, on average, 10 feet (or just over three metres) long, while a Pigmy Right Whale’s baleen plates are only about 2.5 feet, or 0.76 metres in length. The Blue Whale has baleen plates measuring an average length of 3.5 feet (equivalent to one metre) and the Fin Whale’s is about 2.25 feet (or 0.68 metres) in length. In proportion to the body size and, particularly, the size of the head, the baleen plates are rather big. To accommodate such hefty structures, the snout has to be arched.
When the mouth is open (usually in order for the animal to feed), the baleen plates have to extend right from the top of the jaw (where they are attached to the gum) to the bottom so that no food escapes through any gaps. Therefore, the tips of the baleen plates need to be flexible enough to bend inwards so that the whale’s mouth can close unhindered.
There are hundreds of baleen plates on each side of a whale’s mouth. The Blue Whale may have up to 400, while the Pigmy Right Whale has only about 230.
The more rigid the plate, the larger the prey that can be consumed. Whales with flimsier baleen plates commonly have a diet of plankton or krill, which are small and delicate. Those with firmer plates, on the other hand, can consume fish that, while never very large, are a lot more substantial than the krill.
Baleen is made from keratin, the same substance from which human hair and fingernails are made. In terms of its structure, baleen is rather similar to bone, because it consists of a compact layer that encloses three to four layers of horny tube structures. This hollow structure provides the perfect combination of maximum structural strength and minimal weight. The hollow tubes run from the gums, their source, along the full length of the plate and out on the inner edge, emerging as a hollow hair-like structure. The entire baleen plate grows (and continues growing throughout the whale’s life) from the gum out, since its edge is constantly being worn down from use.
The papillae of the baleen plates each have an epidermal fold and a dermal fold that comprises connective tissue, nerves and blood vessels. The epidermis becomes cornified towards the outside of the baleen plate so that the whole top wall of the papillae is made from horn.
As the baleen whale swims through the ocean waters, it keeps its mouth open to allow the water to flow in. The exact feeding methods and characteristics differ slightly amongst the different whale species. The water flows through the tiny gaps between the plates of the baleen, while the krill and (sometimes) fish get stuck in the hairy bristles. The whale then closes its mouth and uses its tongue to push upwards, somehow forcing the captured prey towards and down the throat. Exactly how this is done remains a mystery, as no scientist has been able to see inside the mouth as this process takes place.
The baleen whales make up a significant part of the world’s whale species, and are particularly fascinating in that these mammoth creatures rely on vast amounts of very tiny animals to fulfil their dietary requirements, rather than on hunting larger species, like their toothed relatives.
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