Active hunting by deep-diving sperm whales: 3D dive profiles and maneuvers during bursts of speed

Abstract

Active hunting pursuit can involve high expenditures of energy and therefore requires appropriately high-energy gains from successful prey capture. Using data loggers deployed on 12 sperm whales off the Ogasawara Islands, we regularly recorded bursts of speed during deep dives. Here, we analyzed speed, acceleration, and 3D data from these maneuvers to describe the whales' hunting behavior. Bursts occurred at depths >400 m. The median number of bursts was only 1 per dive (range: 0 to 6 per dive), and 33% of the dives did not include any bursts, suggesting prey capture may not always require bursts. Bursts of speed averaged 3.4 ± 1.0 m s -1 (mean ± SD; maximum: 8 m s -1), more than twice the mean speed observed during dives (1.5 ± 0.2 m s -1). Bursts were generally divided into two phases: (1) rapid acceleration with active stroking, and (2) drastic deceleration and changes in body orientation. Tagged whales swam up to 405 m (mean: 120 ± 88 m) during these two phases. Such behavior suggests chasing of their prey, and should incur high energy expenditure. A large percentage (20 ± 14%) of the drag-related locomotion cost of the dives was spent in bursts. Two major types of bursts were observed: inflectional bursts with turning (87%) and linear bursts without turning (13%). Our results strongly indicate that sperm whales use an active-pursuit hunting strategy and use the bursts only to catch powerful and nutritious prey (i.e. large and/or muscular) that compensate for the energetic cost of the burst. © Inter-Research 2012.