First, he tested a small section of each type of baleen in a flow tank as he varied the flow speed from 10 to 120 cm s and altered the inclination of the baleen to the water flow from parallel to perpendicular. Monitoring the fringes and recording how many beads became lodged for 2 s or more, Werth saw that the bristles trapped most beads at the lowest speeds, and as the flow increased the bristles began streaming like hair, increasing the fringe's porosity and reducing the number of snagged particles: single baleen plates are less effective filters at higher swimming speeds.
However, Werth says, '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; you can't chew anything with just one tooth, you need a whole mouthful.' So, he built a scaled down rack of six, 20 cm long baleen plate fragments and tested how well they trapped the latex beads.
This time, Werth could clearly see the fringes from adjacent baleen plates becoming tangled and more matted as the flow increased, trapping the most particles at speeds ranging from 70 to 80 cm/s, which corresponds exactly with the swimming speed of bowhead whales skimming through shoals of copepods. However, when he compared the porosity of the baleen of both species, he was surprised by the similarity of the performances, despite the whales' different feeding styles.
Having found that baleen filters best at the natural swimming speed of skim-feeding bowheads, Werth is keen to scale up and investigate how full-sized 4 m long baleen plates perform
|Contact: Nicola Stead|
The Company of Biologists