Comportement de chasse des orques (Orcinus orca) autour des îles Crozet

Abstract

Killer whales around Crozet Islands consume a great variety of preys, including fish, penguins (Eudyptes sp.), elephant seals (Mirounga leonina), and, occasionally, large cetacea. Prédation techniques used on elephant seals and penguins, which are easily observed from the shore, are described. Hydrophones were used to record the acoustic behaviour of the whales during their hunts for both types of prey. The successful predation of 29 elephant seals was observed, 24 of which were weaned pups. Seals were captured along the banks (n = 3), near river outlets (n = 14), by voluntary stranding of the whales on the beaches (n = 7), or by attack of seals swimming in bays (n = 5). Hunting techniques were routinely used in "strategic" points apparently chosen specifically according to the location and climatic factors. King penguins were hunted along the banks (n = 13), particularly where algae prevailed, or offshore (n = 32). While hunting, whales tended to be very quiet and used acoustic signals sparingly, emitting a few isolated clicks and short distance contact calls. Reactions of whales exposed to artificial sounds tended to show that they localize their prey by passive listening. When an elephant seal was captured, long distance contact calls characterized by excitement were emitted 72% of the time and resulted in the arrival, by "porpoising," of the most distant members of the group, along with whales of other groups coming from several kilometers away. The author hypothesizes that the adaptive value of this behaviour is to allow the size of the hunting unit to adjust itself to the size of the prey by permitting not only members of the same groupu to associate, but also members of other groups to associate temporarily.[Journal translation]