Characteristics of ringed seal, Phoca hispida, subnivean structures and breeding habitat and their effects on predation

Abstract

Characteristics of ringed seal (Phoca hispida) subnivean structures and breeding habitat were quantified and their potential influence on predation success by polar bears (Ursus maritimus), arctic foxes (Alopex lagopus), and humans on ringed seals was investigated in Admiralty Inlet and Strathcona Sound, Northwest Territories. A total of 237 ringed seal structures were located between April and June 1991–1993 using trained dogs. Ringed seal lairs and breathing holes were concentrated in areas of deep snow, and were associated with large, thick ice ridges. Only a small percentage of the available fast-ice habitat had sufficient snow depth for lair construction each year. A discriminant function analysis used to classify structures located in 1992, using a combination of structural and habitat measurements, correctly classified 70% of structures located in 1991 and 1993 into functional groups. The length, width, internal height, and level of "tiggak," the odour of rutting male ringed seals, associated with structures were the most important descriptors separating structure types. Seventy-three percent of structures located in the study were undisturbed by predators. The mean length and width of structures entered by predators were significantly greater than those of undisturbed structures. Polar bear success decreased as snow depth and the thickness of the roof covering the structures increased. The conditions necessary for successful arctic fox predation are unclear. Inuit hunters attacked structures close to ice ridges, and ridge height and snow depth influenced their success. All predators attacked lairs having the odour of rutting male ringed seals less often than structures with no male odour.