Sonar observations of killer whales (Orcinus orca) feeding on herring schools

Behavior of killer whales feeding on herring schools was recorded with a high frequency (455 kHz) sonar and recorded on a SVHS tape. Synchronization of surfacing behavior of killer whales was analyzed from 8 mm videotapes recorded between 1990–92. Two different feeding techniques, carousel feeding, where killer whales cooperatively herd herring schools into a tight ball towards the surface and feed on herring which have been stunned by tailslaps, and subsurface feeding were observed and compared. Subsurface feeding killer whales showed less coordination and spent less time around the herring schools than carousel feeding killer whales. Both feeding techniques were employed mainly in the upper 20 m of water but only carousel feeding killer whales brought the herring school to the surface. Subsurface feeding killer whales were observed approaching herring schools down to 98 m, but no feeding could be verified when the whales were deeper than 20 m. The possible causes for different techniques employed by killer whales feeding on herring are discussed as well as the apparent similarity of predator–antipredator behavior between schooling fish and their predators regardless of the species in question.