Exploitation of sound during predator-prey interactions: Killer whales and herring

Abstract

The majority of killer whales (Orcinus orca) in Norway and Iceland feed cooperatively on schools of herring (Clupea harengus). The whales swim towards the school and, at short distances, perform underwater tail slaps that produce thudlike sounds containing impulses resembling cavitation pulses in duration, frequencies, and amplitude. Herring are debilitated by the underwater tail slaps, probably due to a combination of factors like sound pressure gradients, particle movements, hydrodynamic effects, and physical contact with the tail or other fish. Following the underwater tail slaps, killer whales can easily capture individual flaccid herring [Simon et al., J. Exp. Biol. 208, 2459–2466 (2005); a video will be shown]. Icelandic killer whales have another strategy not shown by their Norwegian relatives. A whale can emit a 3-s, 680-Hz call that ends 1 s before the tail slap. The frequency of the call falls within the herring audiogram, but outside that of killer whales. This call seems suited for herding the herring into tighter groups, making it possible to debilitate more fish [Simon et al., Behav. Ecol. Sociobiol. (submitted)]. Herring are not defenseless. The school can produce a flatulent bubble net that could hinder detection by killer whale biosonar [Wahlberg Westerberg, Aquatic Living Resources 16, 271–275 (2003)].