Pretty patterns but a simple strategy: predator-prey interactions between juvenile herring and Atlantic puffins observed with multibeam sonar

Abstract

Predator–prey interactions between Atlantic puffins (Fratercula arctica) and newly metamorphosed herring (Clupea harengus) were studied in the Lofoten-Røst area in northern Norway using a high-resolution multibeam sonar system. Attacks from diving puffins and predatory fish induced massive predator-response patterns at the school level, including bend, vacuole, hourglass, pseudopodium, herd, and split. All patterns have previously been observed, using the same sonar, in schools of adult herring attacked by groups of killer whales. Tight ball, the prevailing response pattern in adult fish under predation, was not observed, but a new pattern, intraschool density propagation, was found and interpreted as an analogue to tight-ball formations moving rapidly within the school. The observed patterns persisted much longer than in schools of adult herring attacked by killer whales, reflecting the different hunting strategies. Traditionally, the repertoire of predator responses observed in schooling fish has been interpreted as a range of co operative tactics to trick predators, but this has recently been challenged by authors who suggested that fish that behave the same way produce different patterns at group level simply by maintaining a minimum approach distance to predators and hiding behind conspecifics (the "selfish herd"), and that the particular combination of group size and number and behaviour of predators, rather than different individual tactics, determines the outcome at group level. Our findings support the latter hypothesis.