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 mating 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. Tenure duration (days) followed a heavily skewed, Poisson-like distribution (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 success 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 location of territorial tenure had no measurable effect on mating success (P > 0.05 in both cases). The probability of a male returning to hold 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 success in the current year (P > 0.15). It was, however, positively related to the duration of tenure in the current year (P < 0.0001). The overall annual return rate was 43% which is not significantly different from the survival rate for the general male population and suggests that territorial tenure does not contribute to increased mortality in male Antarctic fur seals.