Meeting Abstract

15.1  Jan. 4  Differences in age at first reproduction of northern sea otters (Enhydra lutris kenyoni) in Alaska VON BIELA, V.R.**; BURNS, J.M.; GILL, V.A.; University of Alaska Anchorage; University of Alaska Anchorage; U.S. Fish and Wildlife Service, Anchorage, AK vanessavb@gmail.com

Life history theory predicts that populations experiencing different environmental conditions such as resource availability and/or predation rates will have different reproduction and survival rates. Age at first reproduction (AFR) is expected to be older if populations are stable or declining due to bottom up constraints and younger if populations are increasing or declining due to top-down factors. In southwest Alaska (SW), where northern sea otter (Enhydra lutris kenyoni) populations have declined over 75% since 1992, changes in AFR may shed light into the causes of the decline. In this study we compared AFR, determined from analysis of reproductive tracts or cementum annuli, between three sea otter populations in Alaska: southcentral (SC, 1994-2005, n=25) where the population is are stable, southeast (SE, 1994-2005, n=39) where the population is stable or increasing, and southwest (SW) during a period when population was stable (1967-71, n = 692) and during the rapid decline (1994-2005, n=42). Otters in SC had the highest AFR of all groups (t-test with Bonferroni correction, p>0.05), as expected for a stable population at carrying capacity. In addition, the AFR for SW sea otters during the decline was significantly lower than when the population was stable (t-test, p>0.05), supporting the hypothesis that top-down forces are driving the current population decline. These findings support the use of AFR as a cost-effective indicator of the underlying causes of population change in large marine vertebrates.