Scaling of Lunge Feeding Kinematics in Baleen Whales

Although gigantic body size and obligate filter feeding mechanisms have evolved in multiple independent vertebrate lineages (mammals and fishes), intermittent ram (lunge) filter feeding is unique to a specific family of baleen whales: rorquals. Lunge feeding is a high cost, high benefit feeding mechanism that requires the integration of unsteady locomotion (i.e. acceleration and maneuvers) and the impact of scale on the biomechanics and energetics of this foraging mode remains poorly understood. The goal of our study was to use a combination of multi-sensor tags paired with drone footage to determine the impact of morphometrics such as body size on kinematic lunging parameters such as fluking duration and timing, maximum lunging speed, and deceleration during the engulfment period. Our preliminary results show that, regardless of size, animals tend to time the cessation of fluking to coincide with both the maximum lunging speed and the point of mouth opening. Given the ability of the rorquals to engulf large volumes of water using their momentum, rather than requiring constant thrust production from the flukes throughout the lunge, we predicted the optimal speed of lunging across scale. In order to minimize the energetic cost of lunge feeding, hydrodynamic theory predicts lower lunge feeding speeds at intermediate body sizes but much higher speeds at the extremes of rorqual body size. We used empirical data to test this theory and to determine how and when rorquals depart from optimal predictions given ecological factors such as differences in prey type and prey distribution. Broadly our results indicate a scale-dependent energetic trade-off between lunge feeding kinematics (cost) and engulfment capacity (gain) that has important implications for the evolution and ecology of gigantic filter feeders.