BEHAVIORAL-DIFFERENCES AMONG ADULT MALE HARBOR SEALS DURING THE BREEDING-SEASON MAY PROVIDE EVIDENCE OF REPRODUCTIVE STRATEGIES

We studied the behaviour of 43 male harbour seals (Phoca vitulina) during the 1991 breeding season on Sable Island, Canada. Males were classified as subadults (n = 21) or adults (n = 22) based on their initial body mass. Throughout the 40-d study, twice-daily beach surveys were carried out to locate marked males. Two spatial (average distance moved between haul outs, and the proportion of possible sightings in which a male was hauled out) and three social (fighting and composition and number of different groups in which the male was observed) variables were used to describe the behaviour of males during the premating period, when there were no, or few, receptive females, and the mating period, when receptive females were increasingly numerous. Of 39 males with complete behavioural data, principal components and cluster analyses identified a subset of 7 adults that differed from the other males. These seven adults exhibited evidence of intermale fighting (i.e., wounding on the neck and hind flippers), showed greater fidelity to a single haul-out site, associated with fewer groups, and were more often sighted alone or in all-male groups. We suggest that these adults may represent the most successful males.