Distribution of sex and age groups of ringed seals Pusa hispida in the fast-ice breeding habitat of Kongsfjorden, Svalbard

摘要

Spatial distribution of various age- and sex groups of ringed seals (N = 94; 19 adult males, 33 adult females and 42 subadults) was studied in their fast-ice breeding habitat in Kongsfjorden, Svalbard, during May 2004. Adult females occupied the inner, most stable ice area, while subadults were found predominantly in the outer parts of the fast-ice, where the ice conditions are more unstable. Adult males were scattered across these 2 areas; some were intermingled with breeding females while others were found further out towards the ice edge in areas mainly dominated by subadults. This pattern suggests territorial behaviour with competitive exclusion of the subadults and adult males that cannot compete for territories in the prime breeding areas. The size of adult males was correlated with their testosterone levels, but it was not necessarily the largest males that had the most adult female neighbors. The adult males that had the most adult female neighbors were however significantly older than the adult males with fewer female neighbors (18 ± 1 vs. 12 ± 1 yr). This suggests that experience (age) likely plays a strong role in achieving reproductive success for male ringed seals. A male:female sex ratio of 1:2.4 was found in the prime breeding area, which suggests a slightly polygynous mating system.