Mating strategies and reproductive success of the male Pacific harbor seal (Phoca vitulina richardsi)

Little is known about mating strategies of pinnipeds that mate underwater. To address this question, I studied male strategies and reproductive success of Pacific harbor seals mating in Elkhorn Slough, California, from 1998 through 2001. Underwater playbacks were used to evaluate the function of male calling behavior. Males responded aggressively to male vocalizations. No responses to control signals were observed. Only one identifiable seal responded per playback location. Female seals did not respond to playbacks. Based upon aggressive male responses, I concluded that vocalizations signal a male's presence, possession of a place and willingness to defend it.; Male mating strategies were studied using VHF telemetry, hydrophone recordings, and additional playbacks. During the mating season, males increased their time in the water and away from haul out locations. At one location, multiple males aggregated to display with activity peaking one month before peak estrus. At two other locations, only one male displayed and acoustic activity was greatest during peak estrus. Small non-adjacent acoustic display areas were observed within the boundaries of large (39,571 +/- 18,818m2) adjacent territories (maritories) defended by males during playbacks. Males exhibited maritory site fidelity for 2--4 years. Benefits gained from defending maritories were unclear, as females moved through freely. This resembles terrestrial lek polygyny.; Elkhorn Slough's travel corridor caused females to be clustered in space and time. I predicted that polygyny would be greater than previously reported for this species in open coast environments without travel corridors. Male reproductive success was measured using microsatellite DNA to determine paternity analysis and sibling relatedness. Most males sired 0 or 1 pup per season with little variation between males, indicating low polygyny. This was confirmed by low levels of sibling relatedness. Males that spent more time in Elkhorn Slough achieved higher reproductive success. A concurrent study observed that approximately 50% of resident females pup elsewhere but don't ovulate until returning to Elkhorn Slough suggesting females mate preferentially with known males of shared home range (Greig 2002). It appeared that environments with travel corridors favored inshore male strategies, but polygyny was no greater than reported for open coast habitats.