Herring schooling manoeuvres in response to killer whale attacks

• Published in: Canadian Journal of Zoology
• Main Authors: Nøttestad, Leif, Axelsen, Bjørn Erik
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1999
• Subjects: Killer Whale; Orca; Orcinus orca; Tysfjord; Killer whale
• Online Access: http://dx.doi.org/10.1139/z99-124; http://www.nrcresearchpress.com/doi/pdf/10.1139/z99-124

The antipredator behaviour of overwintering Norwegian spring-spawning herring (Clupea harengus L.) was investigated during repeated attacks by killer whales (Orcinus orca L.) in Tysfjord in northwestern Norway. The observations were made using a high-resolution (455 kHz) multibeam sonar. Ten different types of predator-prey interactions were recorded during 54 observed events (an average of one antipredator event every 3.9 min). Antipredator responses 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. Attacked schools were significantly more circular (p < 0.0001) and had higher relative densities (p < 0.05) than schools that were not attacked.