The influence of rookery terrain on population structure, territorial behavior, and breeding success of Steller sea lions in the Gulf of Alaska

Abstract

The effect of rookery terrain on population structure, territorial behavior and breeding success of Steller sea lions was assessed at two rookeries, in the northern Gulf of Alaska. The sea lions using Sugar loaf and Marmot Islands differed in age structure, juveniles being absent from Sugar loaf but present on Marmot during the breeding season. Territory boundaries of breeding bulls on Sugarloaf were stable, and were unaffected by tides. Territory boundaries on Marmot were unstable, shifting with the tide. Territorial bulls occupied two types of territories on Sugarloaf Island (landlocked and water-access) and three types on Marmot (landlocked, tidal and semiaquatic). The behavior of territorial bulls on Marmot was influenced by tides and presence of juvenile animals. These factors were not important on Sugarloaf. The breeding success of territorial bulls was unaffected by location of territory on Sugarloaf. Territory location was important in the breeding success of Marmot Island bulls.