The behavior of Pacific herring schools in response to artificial humpback whale bubbles

Abstract

There have been numerous reports of humpback whales and other marine predators deploying bubbles during foraging activities. However, the effects of bubbles on schooling prey organisms remain poorly understood. We conducted a series of laboratory experiments to gain insight into the effect of bubbles on the Pacific herring, Clupea harengus pallasi, a principal prey species of the humpback whale, Megaptera novaeangliae. The fish exhibited strong avoidance of bubbles and could be contained within a circular bubble net. The herring schools were also reluctant to swim through a curtain of bubbles even when frightened. However, herring were much more willing to cross a bubble curtain or net if there was a larger aggregation of fish on the opposite side. Individuals and small groups of herring also waited for less time before crossing than did larger groups. These experiments suggest that herring have a strong fear of bubbles and can readily be manipulated or contained within bubble nets by predators.