Meeting Abstract
P3.132 Thursday, Jan. 6 Passive elasticity of ventral groove blubber does not limit engulfment volume in lunge-feeding whales GOLDBOGEN, Jeremy, A.*; POTVIN, Jean; SHADWICK, Robert, E.; University of California, San Diego; Saint Louis University; University of British Columbia jergold@ucsd.edu
Rorqual whales feed by engulfing large volumes of water containing schooling prey. The ability to engulf a mass of water on the order of the entire body mass is facilitated by highly compliant ventral groove blubber (VGB) and underlying muscle that make up the buccal cavity outer wall. An early study of non-linear elasticity in fin whale VGB proposed that engulfment volume was determined by the elastic limit of this tissue, a strain of about 300% (Orton and Brodie, 1987, Can. J. Zool.) This model invoked flow-induced passive inflation, i.e. with muscles inactive during stretching of VGB. More recently we formulated a model where active resistance by the VGB muscles is necessary to control the rate and amount of buccal cavity inflation and to accelerate the engulfed water (Potvin et al. 2009, J. Royal Soc. Interface), suggesting that the engulfed volume and maximum VGB strain is not set by its passive elastic properties. We investigated this idea in two ways. First, we calculated the maximum volume of the buccal cavity using geometries based on photographic evidence of lunge feeding whales in the field, and then estimated the resulting circumferential VGB strain. Secondly, we measured VGB strain from the relative separation of adjacent ridges seen in photos of lunging fin, blue, minke and bryde’s whales. In both cases we determined that at full engulfment the VGB experiences circumferential strain of only about 150%, or half what a totally passive inflation would cause. In contrast, strains measured from photos of dead, fully bloated whales reached as high as 300%, the elastic limit of the tissue. Our results suggest the VGB muscle layer plays an active role in buccal cavity inflation, likely by eccentric contraction.
