Polar bear predation on beluga in the Canadian Arctic

摘要

During May 1970, while conducting field work at Grise Fiord in the Canadian Arctic Archipelago, a local hunter reported that a polar bear (Ursus maritimus) had successfully caught 3 beluga (Delphinapterus leucas) during March near King Edward VII Point (76°08' N, 81°08' W), the extreme southeast cape of Ellesmere Island, Northwest Territories. As none of the fifteen local hunters had ever witnessed such an event, and only one had ever heard of it before, I assumed bear predation on whales to be very rare, and consequently recorded whatever information I could obtain at the time. According to the hunter's narrative, movement of a partially grounded iceberg about 200 metres offshore had prevented freezing of a small area of water surrounding the berg. ... it seems probable that a small number of beluga had endeavoured to pass the winter in the open water alongside this berg. At some time in March a medium-sized female bear had caught and removed an adult female beluga together with another adult and a grey-coloured subadult beluga both of unspecified sex; the adult female beluga was dragged about 7 metres from the edge of the water, the other two a shorter distance only. ... Four days later on reaching the site of the whale kill, only the carcass of the grey beluga remained; apparently movement of the berg had broken up the ice and no trace of the other two carcasses could be found. The remaining carcass was attracting large numbers of glaucous gulls (Larus hyperboreus) and some ravens (Corvus corax) and earlier that day two male bears had been present. The smaller of the two bears had walked backwards dragging the beluga carcass tail-first in a zig-zag course a distance of about 150 metres from an earlier resting place on the ice. Inspection of the carcass indicated loss of all skin and fat, and most of the meat from head and trunk; fracture of the occipital bones had occurred, but it is not known if this damage was suffered before or after death. An eyewitness account of a polar bear killing beluga in Novaya Zemblya however, relates how the bear lies with outstretched paws on the ice and delivers a blow to the head when the whale surfaces within range. ... There appears no reason to doubt that the hunter reporting this event had, as he believed, discovered the beluga shortly after they were caught in March, nor that the tracks of the medium-sized female bear near the carcasses at that time were those of the predator. According to the description given, such a bear would weigh in the range of 130 to 180 kilograms, or about one-fifth the probable weight of each adult beluga it had successfully killed and removed from the water. The only other reports on bears killing beluga I can find in the literature appear contradictory. One asserts that, in the Baffin Bay region, at small openings in the ice where whales are sometimes trapped in winter, "a small flock of bears will congregate and kill a small whale, which they will then drag up on to the ice and eat". The other commentary, relating to the Eurasian arctic, suggests that attacks on beluga by single bears are quite frequent, and that when a bear discovers a pod of trapped whales it remains nearby and successively kills them (up to 13 are reliably reported). This present report of a multiple killing by a solitary bear, substantiated by direct inspection shortly after the event, establishes that there is no difference between Eurasian and North American polar bears in regard to this predatory behaviour