A long-term study reveals multiple reproductive behavior strategies among territorial adult male Steller sea lions (Eumetopias jubatus)

Abstract

We conducted a long-term study to assess how tenure and territorial behaviors influence reproductive success among male Steller sea lions (Eumetopias jubatus (Schreber, 1776)). Copulations by males (n = 44) that maintained territories on a rookery in the Gulf of Alaska from 2001 to 2009 were observed using a remote video system. Approximately half of postpartum females copulated with a male in a different territory from where they gave birth. Nearly two-thirds of territorial males with known tenure were unsuccessful in copulating during their first year. Number of copulations for territorial males increased from acquisition year to year 2 with no change in subsequent years. Cluster analysis of tenure and territorial tactic variables for 15 males with observed lifetime reproductive success was used to describe multiple reproductive strategies. Characteristics of the two most successful strategies were the following: (i) males typically copulated in their first year, retained the same territories for 3–5 years, and occupied centrally located coastal territories where the highest percentage of females gave birth and (ii) males did not copulate until at least their third year and occupied peripheral territories with fewer births for a longer tenure of 7–8 years. Results indicated that lifetime reproductive success was not achieved solely by time on the breeding area; rather, it was achieved from a combination of tenure and territorial tactics.