March 14, 2013
Whales’ Baleen Teeth Entangle Prey With Hairy Fringes
Brett Smith for redOrbit.com - Your Universe Online
Whether they hunt for food by opening their mouths while diving deep into the ocean or skimming along its surface, many whale species rely on their baleen teeth to filter tasty morsels from the mouthfuls of seawater they take in.
According to Alexander Werth, a biology professor from Hampden-Sydney College in Virginia, no one has ever looked into the mechanism behind how the hairy substance actually traps food.
“The standard view was that baleen is just a static material and people had never thought of it moving or that its function would be altered by the flow of water through the mouth,” Werth explained.
Werth found that the baleen system actually works best by entangling food as water flows across it, according to his report in The Journal of Experimental Biology.
Composed primarily of the protein keratin, baleen is a system of large, continually growing plate-like structures with an internal fiber core and a smooth exterior. These plates are continually worn away by the whale´s tongue, forming bristly fringes that are capable of trapping food.
Most whale mouths contain about 300 baleen ℠plates´ and the structure of baleen systems can vary from whale to whale. For example, the hairy baleen fringes of the skim-feeding bowhead whale are twice as long as the fringes on the dive-feeding humpback whale.
According to Werth, he became fascinated with baleen while performing his postdoctoral work with the Inupiat Eskimos of Barrow, Alaska. After collecting baleen samples from ram-feeding bowheads in Alaska, Werth decided to compare them with samples of humpback baleen that he had collected as a graduate student.
He began by trying to see how well the baleen trapped small latex beads carried by flowing water. Taking a small section of each type of baleen, Werth place each sample in a flow tank and watched as he varied the flow of the water from 4 to 47 inches per second. He also changed the inclination of the baleen, allowing the water to flow from parallel to perpendicular.
While making adjustments to his experimental settings, Werth monitored the baleen and recorded how many beads were trapped for 2 seconds or more. He found that the bristles trapped most beads at the lowest speeds. As the flow speed increased, the marine biologist saw the baleen fringes act more like hair, allowing more beads to pass through. This indicated that single baleen plates are less effective filters at higher swimming speeds.
However, Werth said that the results of this set of experiments were inconclusive.
“'It doesn't make sense to look at flow across a single plate of baleen, it's like looking at feeding with a single tooth,” he said. “You can't chew anything with just one tooth, you need a whole mouthful.”
To refine his experiment, Werth built a scale model rack of six baleen plate fragments and tested the larger system for its ability to trap the latex beads. This setup resulted in the baleen becoming tangled and matted at flow speed that closely mirror the average swimming speeds of these whales.
Encouraged by these results, Werth said he plans to scale up his experimental baleen systems to get a more comprehensive picture of how they enable whales to feed.