Skull and buccal cavity allometry increase mass-specific engulfment capacity in fin whales

Abstract

Rorqual whales (Balaenopteridae) represent not only some of the largest animals of all time, but also exhibit a wide range in intraspecific and interspecific body size. Balaenopterids are characterized by their extreme lunge-feeding behaviour, a dynamic process that involves the engulfment of a large volume of prey-laden water at a high energetic cost. To investigate the consequences of scale and morphology on lunge-feeding performance, we determined allometric equations for fin whale body dimensions and engulfment capacity. Our analysis demonstrates that larger fin whales have larger skulls and larger buccal cavities relative to body size. Together, these data suggest that engulfment volume is also allometric, increasing with body length as L 3:5 body . The positive allometry of the skull is accompanied by negative allometry in the tail region. The relative shortening of the tail may represent a trade-off for investing all growth-related resources in the anterior region of the body. Although enhanced engulfment volume will increase foraging efficiency, the work (energy) required to accelerate the engulfed water mass during engulfment will be relatively higher in larger rorquals. If the mass-specific energetic cost of a lunge increases with body size, it will have major consequences for rorqual foraging ecology and evolution.

On the Olfactory Anatomy in an Archaic Whale (Protocetidae, Cetacea) and the Minke Whale Balaenoptera acutorostrata (Balaenopteridae, Cetacea)

“…The conspicuous forward thrust of the vertex in balaenopterids (in both absolute distance and proportionally when compared with both archaeocetes and odontocetes) is likely a consequence of their evolutionary preference toward bulk feeding. This mode of prey capture is described elsewhere and the energetics involved therein continues to be the focus of research attention (Pivorunas, 1977(Pivorunas, , 1979Lambertsen, 1983;Lambertsen et al, 1995;Goldbogen et al, 2007Goldbogen et al, , 2008Goldbogen et al, , 2010Goldbogen et al, , 2011Goldbogen, 2010;Pyenson et al, 2012). It is not yet known how much force is needed to close balaenopterid jaws once the pleated throat is engorged with food-laden water, but at the very least, most of that force has to come from jaw adductor musculature, which in turn take their origin on the skull (Beauregard, 1882;Beneden, 1882;Lambertsen et al, 1995).…”

Keeping momentum with a mouthful of water: behavior and kinematics of humpback whale lunge feeding

“…However, analysis of our fine-scale accelerometer and depth data suggests a different interpretation of this signal. In the following, we will discuss the details of humpback lunge feeding as revealed by these data and address implications for the existing models for rorqual feeding behavior and kinematics (Goldbogen et al, 2009;Goldbogen et al, 2010;Potvin et al, 2009;Potvin et al, 2010).…”

“…Accelerating the body from a near stop after each lunge, as required by this model, is energetically costly and is purported to be the key factor determining oxygen consumption in lunge feeding (Goldbogen et al, 2006;Goldbogen et al, 2007;Goldbogen et al, 2010). However, there are several difficulties with the lunge-stop model and the measurements on which it is based, making it uncertain precisely when key biomechanical events occur in lunges.…”

“…Ideally, we would sample the whale's velocity and the relative timing of the mouth opening and closing, but sensors for gape on wild cetaceans are not currently available, and extant speed sensors are directional and so must be calibrated in situ over the behaviors of interest to approximate forward speed (Blackwell et al, 1999;Shepard et al, 2008). In their studies, Goldbogen et al (Goldbogen et al, 2006;Goldbogen et al, 2007;Goldbogen et al, 2010;Goldbogen et al, 2011) relied on the amplitude of low-frequency flow noise, recorded by the tag, as a proxy for speed whereas the mouth opening state was deduced by combining speed and stroking indications derived from tag accelerometers sampled at 1Hz. Although care was taken to calibrate flow noise against the known descent and ascent speeds of each tagged animal, the relationship between flow noise and forward speed also depends on the body form and gait, both of which change dramatically during lunges.…”

“…Based on these recordings, Goldbogen et al (Goldbogen et al, 2006;Goldbogen et al, 2007;Goldbogen et al, 2010) proposed a lunge-stop model for lunge feeding in which the whale first accelerates to >3ms -1 and then opens its jaws, initiating a rapid deceleration due to the increased drag force from a radically changed body form. This deceleration ultimately brings the whale to a near standstill at the end of the lunge, requiring additional fluke strokes for the whale to regain forward motion.…”