Big gulps require high drag for fin whale lunge feeding

Abstract

Fin whales Balaenoptera physalus exhibit one of the most extreme feeding methods among aquatic vertebrates. Fin whales, and other rorquals (Balaenopteridae), lunge with their mouth fully agape, thereby generating dynamic pressure to stretch their mouth around a large volume of prey-laden water, which is then filtered by racks of baleen. Despite their large body size, fin whales appear to be limited to short dive durations, likely because of the energetic cost associated with large accelerations of the body during several lunges at depth. Here, we incorporate kinematic data from high-resolution digital tags and morphological data of the engulfment apparatus in a simple mechanical model to estimate the drag acting on a lunge-feeding fin whale. This model also allowed us to quantify the amount of water and prey obtained in a single lunge. Our analysis suggests that the reconfiguration and expansion of the buccal cavity enables an adult fin whale to engulf approximately 60 to 82 m 3 of water, a volume greater than its entire body. This large engulfment capacity, however, comes at a high cost because the drag, work against drag, and drag coefficient dramatically increase over the course of a lunge. As a result, kinetic energy is rapidly dissipated from the body, and each subsequent lunge requires acceleration from rest. Despite this high cost, living balaenopterids are not only among the largest animals on earth, but are relatively speciose and exhibit diverse prey preferences. Given this ecological diversity, we frame our results in an evolutionary context, and address the implications of our results for the origin of lunge feeding.

Discovery of a sensory organ that coordinates lunge feeding in rorqual whales

“…In terms of lunge-feeding kinematics, anatomical and histological evidence suggest that the organ's mechanosensors assist in controlling and providing neurological information about the configuration of the jaws during rapid lunges. We propose a three-step lunge-feeding model to explain the organ's role during a lunge: (1) using vibrissae present on the external surface of the chin 9 , rorquals register prey fields of sufficient density; (2) the jaws disengage and rotate 6 , thereby compressing and shearing the organ; and (3) the oropharyngeal cavity reaches full expansion, with drag forces acting on the inside of the mouth 17,18 transmitted to the organ through the YSF 8 (Fig. 2).…”

“…In fin whales (Balaenoptera physalus), for example, the entire process of a lunge occurs in a short time span (,6 s), during which approximately 60-80 m 3 of water and prey are engulfed, a volume equal to or greater than that of the individual rorqual itself 17 ( Fig. 1).…”

Convergent Evolution Driven by Similar Feeding Mechanics in Balaenopterid Whales and Pelicans

“…During an engulfment-feeding event in these taxa, the extensible tissue comprising the floor of the mouth expands enormously, generating a highly unstreamlined profile. An open mouth moving at high speed underwater generates considerable pressure drag, the same phenomenon that provides resistance to moving an open bag under water (Goldbogen et al, 2007). Additionally, rorquals actively accelerate water in their buccal cavities after a lunge-feeding event, giving rise to ''engulfment drag'' (Potvin et al, 2009).…”

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

“…Furthermore, theories and mechanisms regarding limits to large body size in whales are rare (Alexander 1998), probably because of our general lack of knowledge about the physiology of these animals. Recent advances in digital tag technology have revolutionized the study of rorquals in their natural environment, especially with respect to foraging mechanics and energetics (Acevedo-Gutierrez et al 2002;Croll et al 2005;Goldbogen et al 2007Goldbogen et al , 2008Bailey et al in press). Integrating these data provides novel opportunities to examine how animals function at the outlying limits of body mass and also to explore the physiological limits to body size.…”

“…Rorquals meet this energetic demand using a bulk-filterfeeding strategy, lunge feeding, which involves the engulfment and filtering of a large volume of prey-laden sea water that is commensurate of their body size (Goldbogen et al 2007). This tremendous engulfment capacity, however, does not come without a cost.…”