Meeting Abstract
Baleen whales are filter feeders, consuming aggregations of zooplankton from the water column using baleen plates inside the mouth. Baleen consists of keratin plates arranged in racks, which fray on the inside edge and create a dense fibrous mat. Baleen whales include some of the largest animals on the planet, which support themselves on vast numbers of small-bodied organisms by filter feeding. Despite the importance of baleen filtration to the natural history and ecology of these predators, very little is known about either three-dimensional baleen morphology or the mechanics of baleen filtration, including what role, if any, the fringe plays in filtration. To quantify the three-dimensional morphology of baleen plates, we used computed tomography (CT) to image partial baleen racks from five species. For each baleen specimen, we calculated the percentage by volume of both plate material and the complementary void between plates for seawater flow during filtration. By volume, baleen plates comprised 14-34% of the imaged racks. The sei whale specimen had the smallest plate and largest void volumes, while the gray whale specimen had the largest plate and smallest void volumes. The relationship between plate/void volume between species likely reflects the functional constraints associated with foraging on different prey items, as well as differences in filter feeding strategies. We also investigated whether the baleen fringe modulates flow through baleen plates using a gravity-driven water flume. Flow rates through partial racks of baleen from a blue whale, a humpback whale, and a fin whale were not significantly different than the flume’s flow rate with no baleen, suggesting that neither the fringe mat nor the baleen plates produce significant hydrodynamic resistance during filter feeding.
