KOT, B.W.; University of California, Los Angeles: Ventral Pouch Flow Dynamics in Feeding Rorqual Whales: A Kinematic Analysis

Rorqual whales (Family: Balaenopteridae) capture prey intermittently by lunging into masses of prey organisms. They employ their unique filter-feeding anatomy to engulf prey and seawater. Due to the impossibility of directly investigating internal flow dynamics in wild rorquals, I have used indirect observations and measurements to study aspects of these flow movements. Field observations and video capture of surface-feeding rorquals took place in the Gulf of St. Lawrence, Canada. As lunging rorquals broke the surface their engulfed volumes of water often generated conspicuous waves in the outer walls of their ventral pouches. The movement of these waves provided signatures of internal flow movement. Two-dimensional kinematics of the waves were analyzed from digital video of three species of rorquals. Individual still frames were extracted from video sequences and digital landmarks were placed on the anterior margin of individual waves. This allowed flow movement, relative to the animal, to be calculated over known time intervals. The flow traveled back into the pouch then rebounded back toward the rostrum. Flow velocity was quantified and the momentum of the rebound is thought to help initiate ram filtration through the baleen plates. Minke whales (Balaenoptera acutorostrata; the smallest species) showed the slowest rebound, with finback whales (B. physalus; intermediate in size) and blue whales (B. musculus; the largest species) each being progressively faster. Previous studies concerning the function of the ventral pouch have mostly come from morphological investigations of postmortem specimens. This study is the first, to the best of my knowledge, to quantify ventral pouch flow dynamics in wild rorqual whales.