No abstract

No abstract

No abstract

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 m2 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.

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 cooperative 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.Résumé : Nous avons étudié les interactions prédateurs-proies entre des Macareux moines (Fratercula arctica) et des Harengs (Clupea harengus) fraîchement métamorphosés dans la région de Lofoten-Røst, dans le nord de la Norvège au moyen d'un sonar de haute résolution à faisceaux multiples. Les attaques des oiseaux en plongée et des poissons prédateurs déclenchent des patterns de réaction massive au sein des bancs de harengs : repliement, vacuole, sablier, pseudopode, troupeau et séparation, types de comportement déjà observés, au moyen du même sonar, dans des bancs de harengs adultes attaqués par des épaulards. La formation d'une boule compacte, la réaction la plus fréquente des poissons adultes face à des prédateurs, n'a pas été observée, mais il s'est produit un nouveau pattern dans les bancs de harengs, la pulsion de densité, interprétée comme analogue à la formation d'une boule compacte, mais se déplaçant rapidement dans le banc. Ces patterns ont duré beaucoup plus longtemps que ceux observés dans les bancs de harengs adultes attaqués par des épaulards, ce qui reflète la diversité des stratégies de chasse. Traditionnellement, le répertoire des réactions aux prédateurs observé au sein des bancs de poissons est considéré comme une série de tactiques de coopération pour tromper les prédateurs, mais cette théorie a été remise en question par les auteurs qui croient que ces poissons qui se comportent de la même façon produisent des patterns différents quand ils sont en groupe en s'approchant...