Meeting Abstract

9.8  Jan. 4  The Ventral Pouches of Lunge-Feeding Great Whales Play Central Dynamic Roles in Prey Capture and Filtration KOT, B.W.; Univ. of California, Los Angeles bkot@ucla.edu

Among the largest and most visible anatomical features of the great whales (rorquals; Mammalia: Balaenoptera) are their antero-ventral pleated pouches. These pouches are major components of the filter feeding apparatus of the whales and extend from the tips of the lower jaw posterior to nearly the umbilicus. The understanding of how they function during feeding remains mostly qualitative and speculative. Most rorquals capture prey by lunging into masses of prey organisms such as schooling krill or fishes. Due to the impossibility of directly investigating internal flows in the buccal cavities of feeding wild rorquals, I have used external observations and measurements to study aspects of these flows. Visual observations and digital video recordings were made of three species of rorquals feeding at the sea surface in the Gulf of St. Lawrence, Canada. Blue whales (Balaenoptera musculus; the largest species), finback whales (Balaenoptera physalus; intermediate in size), and minke whales (Balaenoptera acutorostrata; the smallest species) were observed while actively feeding on prey at the surface. As lunging rorquals opened their mouths and partially emerged from the water three things happened: they turned on their sides or backs, exposing their ventral pouches; their forward motions rapidly slowed; and the engulfed volumes of water generated conspicuous waves (moving bulges) in the outer walls of the pouches. Two-dimensional kinematics of the waves were estimated from video recordings of the three species. Results show that these rorquals use their ventral pouches in a functionally similar manner despite their large differences in body size and mass. The evident elasticity of the pouch may also help maintain elevated internal water pressures necessary for the completion of filtration.