Rorqual whales (Balaenopteridae) are obligate lunge filter feeders that intermittently engulf and process large volumes of prey-laden water. Lunge feeding is a high-cost (due to drag), high-benefit (due to the amount of food captured) strategy that has major implications for rorqual diving capacity and foraging ecology, but several biomechanical aspects of this feeding strategy and its energetic consequences remain unknown. A complex suite of morphological adaptations, the most important of which is the ventral groove blubber (VGB), enable the rapid inflation and extreme expansion of the oral cavity during lunge feeding events. The mechanical properties of the VGB suggest that flow-induced dynamic pressure generated from high swimming speed is required to fully expand the ventral feeding pouch. Previous tag studies of lunge feeding have largely lacked detailed information on the timing of mouth opening and VGB expansion relative to specific kinematic signatures. Here we used a custom engineered tag that included dual video cameras and high-resolution movement sensors (accelerometers, magnetometers, and gyroscopes) to simultaneously measure the strain of the VGB and the mechanics of the body during 8 lunge-feeding events in 4 tagged blue whales. Our analyses indicated that VGB expansion proceeds posteriorly, with anterior regions reaching maximum extension prior to the initial expansion of posterior regions. Body deceleration began at the onset of mouth opening and ended when the VGB reached maximum extension. Our estimates of maximum VGB strain in blue whales (1.80 ± 0.23) was significantly lower than its known mechanical limit (3.0). These results support the hypothesis that engulfment requires the use of eccentric muscle to actively resist inflation as water and prey enter the mouth. By action-reaction, active inflation generates additional drag that has a significant effect on the energetics of lunge feeding.
Citation:
Cade, D, J Calambokidis, A Friedlaender, and J Goldbogen. 2015. Expansion rates of ventral groove blubber in lunge-feeding blue whales. Abstract (Proceedings) 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, California, December 14-18, 2015.