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Mechanics and energetics of rorqual lunge feeding Goldbogen, Jeremy Arthur

Abstract

Rorquals whales are among the largest predators on earth, yet little is known about their foraging behavior at depth. These whales obtain their prey by lunge-feeding, an extraordinary biomechanical event where large amounts of water and prey are engulfed and filtered. This process is predicted to entail a high energetic cost that has major consequences for rorqual foraging ecology and efficiency. The present thesis examined the mechanics and energetics of lunge feeding using a combination of experimental and theoretical analyses. Body kinematics and respiratory events during foraging were determined using a digital acoustic tag. Kinematic data were incorporated into a hydrodynamic model of lunge feeding to calculate engulfment drag and volume. Finally, an allometric analysis was used to assess the effects of size and morphology on lunge feeding performance. The tag data demonstrate that rorquals glide to depth, execute several lunges at the bottom of a dive, and ascend to surface via active swimming strokes. Each lunge is marked by a rapid increase and decrease in body speed and a bout of active swimming strokes. During a lunge, a rorqual can engulf a volume of prey-laden water that is larger than its entire body, but at a high energetic cost because the drag, work against drag, and drag coefficient dramatically increase during the lunge. The allometry of rorqual feeding morphology enhances engulfment capacity, but at a higher energetic cost. Longer dives were required to perform more lunges at depth and these extended apneas were followed by an increase in the number of breaths taken after a dive. Maximum dive durations during foraging were approximately half of those for non-feeding whales. At the highest lunge frequencies, respiratory rate was at least threefold higher than that of non-feeding whales that underwent a similar degree of apnea. This thesis provided several lines of evidence that support the concept of high foraging costs in rorquals associated with lunge feeding. Despite this high cost, rorquals are able to sustain some of the largest animal masses that have ever existed, but it may also impose an upper limit on large body size in this lineage.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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