Meeting Abstract

40.5  Saturday, Jan. 5  Fish versus krill " Comparing the energetic costs of engulfment by rorqual whales lunge-feeding on slow and fast prey POTVIN, J*; GOLDBOGEN, J A; SHADWICK, R E; PYENSON, N D; Saint Louis University; Cascadia Research Collective; Univ. of British Columbia; Smithsonian Institution

Lunge feeding is a strategy employed by rorquals (Balaenopteridae) to catch schooling krill or (small) fish in bulk, via the engulfment of the water in which the prey is embedded. Recent modeling informed with kinematic and morphological data (Goldbogen et al 2012 Func Ecol; Potvin et al. 2012 PLoS One) indicate that lunge feeding on krill comes at high costs, largely incurred from quickly setting into motion a very high mass of water. Particularly with regards to the expended metabolic power, such costs are high enough at large body lengths to impose a physical limit on the largest size attainable by these whales. Whether the same mandible kinematics (mouth opening rates and maximum gape), body-water dynamics and body size limit involved in krill-feeding apply to the engulfment of fish has never been assessed. Here we show via modeling that, due to the significantly higher escape speeds of the prey, such extrapolation involves unrealistically high metabolic outputs, as well as mouth opening rates that are much higher than measured by tags deployed on humpback whales (horizontally lunging towards fish). On the other hand, fish-engulfment costs become smaller and more realistic, i.e. similar or lower than the highest active metabolic output of any terrestrial mammals (mass-specific), if engulfment is modified by resorting to smaller maximal gapes (i.e., 50 rather than 80deg) and by keeping the mouth opened over longer durations (i.e., 2-3 time longer than for krill-feeding). Also, applying such revised lunging kinematics over the body size spectrum of humpback and fin whales shows costs decreasing with the smaller bodies and trending to levels characteristic of krill-feeding.