THE COST AND BENEFITS OF TERRITORIAL TENURE, AND FACTORS AFFECTING MATING SUCCESS IN MALE ANTARCTIC FUR SEALS

The timing, location and duration of territorial tenure, and the matin g success and return rates of male Antarctic fur seals (Arctocephalus gazella) were measured over four consecutive breeding seasons (1984-87 ) on Bird Island (54 degrees 00'S, 38 degrees 02'W), South Georgia. Te nure duration (days) followed a heavily skewed, Poisson-like distribut ion (median 13.08 days, maximum 75 days) and was positively related to the number of years of tenure (r(s) = 0.52, P < 0.0001). Mating succe ss was also biased to a few individuals and was positively correlated to both duration of tenure (days) and the previous number of years in which tenure was achieved (P < 0.0001 in both cases). The timing and l ocation of territorial tenure had no measurable effect on mating succe ss (P > 0.05 in both cases). The probability of a male returning to ho ld a territory in the next year was not related to the number of years tenure that had been achieved (P > 0.7) or to the level of mating suc cess in the current year (P > 0.15). It was, however, positively relat ed to the duration of tenure in the current year (P < 0.0001). The ove rall annual return rate was 43% which is not significantly different f rom the survival rate for the general male population and suggests tha t territorial tenure does not contribute to increased mortality in mal e Antarctic fur seals.