Herring schooling manoeuvres in response to killer whale attacks

The antipredator behaviour of overwintering Norwegian spring-spawning herri ng (Clupea harengus L.) was investigated during repeated attacks by killer whales (Orcinus orca L.) in Tysfjord in northwestern Norway. The observatio ns were made using a high-resolution (455 kHz) multibeam sonar. Ten differe nt types of predator-prey interactions were recorded during 54 observed eve nts (an average of one antipredator event every 3.9 min). Antipredator resp onses included "split," "hourglass," "vacuole," "bend," "dive," "herd," and "fountain." Large attacked schools demonstrated a different repertoire of antipredator manoeuvres than small ones and were less likely to be attacked . Despite being located in the vicinity of the whales, herring schools with a cross section exceeding 460 m(2) were not attacked by killer whales. Att acked schools were significantly more circular (p < 0.0001) and had higher relative densities (p < 0.05) than schools that were not attacked.