Aquatic territory defence by male harbour seals (Phoca vitulina) at Miquelon: Relationship between active defence and male reproductive success

Pinnipeds have unique phylogenetic and environmental constraints which increase the potential for male polygyny. Most of the land-breeding species are polygynous. Less is known about the mating systems of water-breeding pinnipeds, like harbour seals. Harbour seals have many characteristics which suggest at least a low level of polygyny. The purpose of this study is to determine: (1) if male harbour seals are competing for females by displays and/or territorial maintenance and (2) whether these competitive tactics are linked to siring progeny.;The paternity results from DNA fingerprinting, using Jeffreys' 33.15 and 33.6 probes on a captive group, indicated that this technique could be used successfully to determine paternities in harbour seals. Observed copulation did not predict male reproductive success.;Paternity tests were conducted on five adult males and thirteen mother-pup pairs, caught in one study area at Miquelon. Two mother-pup pairs were excluded from the paternity analyses, as they had very low band-sharing coefficients suggesting that these females were fostering pups. Three of the displaying males had fathered pups, while one displaying male and non-displaying male had not.;The aquatic display behaviour, haul-out patterns and aggressive interactions of nine identified males were video-taped during two consecutive breeding seasons. Site-specific simultaneous displays occurred regularly between neighbouring males, establishing territory boundaries. Males defending more boundaries displayed at significantly higher rates than males with fewer boundaries. These results indicated that displays were for boundary defence and not self-advertisement. Intruder males were forced from haul-out areas through aggressive interactions. Territorial males did father some pups suggesting that there is reproductive success associated with territory defence. Some males were never seen displaying and may have been adopting an alternate mating strategy. The deep channels at Miquelon create physically bounded-water ways through which females and pups must pass. The topography at Miquelon appears to facilitate aquatic territory establishment and the defence of areas proximate to females.