OBSERVATORY; On Dives, Hungry Whales Go Slow and Open Wide
By HENRY FOUNTAIN
Published: August 25, 2009
The bowhead whale has a tough task when it comes to diving and feeding. Opening its huge mouth to expose its baleen plates, so it can filter plankton and other organisms from seawater, creates a lot of extra drag. But the bowhead has only a limited supply of oxygen for each dive.
What's the whale to do? It could filter-feed only occasionally, or it could feed continuously but slow down. Either way reduces drag, and thus the energy expended.
Malene Simon of Aarhus University in Denmark and colleagues studied bowheads feeding off West Greenland by attaching small acoustic tags (developed by two of the study's authors, Mark Johnson and Peter Tyack) that also contain pressure sensors to record depth and accelerometers and magnetometers to record the whale's orientation.
As the researchers report in The Proceedings of the Royal Society B: Biological Sciences, at the bottom of their dives the whales moved at very slow speeds, less than three feet per second, continuously using their tails, or flukes, to propel them. That suggests they kept their mouths open for filter-feeding throughout the bottom part of the dives.
Despite the slow speed, the researchers calculate that the whales can filter about 100 cubic feet of water per second, or more than 2,000 tons of water and prey during a typical dive.
PHOTO: An Atlantic bowhead whale near Baffin Island, in Canada.(PHOTOGRAPH BY PAUL NICKLEN/GETTY IMAGES)