Spatial and temporal variation in sea otter demography

1) Better information on historical and current population dynamics is central to understanding patterns of growth and decline in the California sea otter population. We developed a maximum likelihood-based analytical method to estimate historical age/sex specific vital rates as well as spatial and temporal variation in vital rates from longitudinal databases on population census numbers and the age-structure of salvaged carcasses.

2) We estimated current demographic parameters by conducting a mark-recapture study, measuring survival and reproduction of 115 radio-tagged individuals between 2001 and 2004. These current estimates were compared to estimates from a similar study of radiotagged otters conducted in the mid-eighties.

3) Together, these two approaches indicated that survival has decreased substantially between the early 1990s and the present and is lowest in the north-central portion of the population's range.

4) The greatest decrease in survival was for adult females (≥ 4 years of age). Variation in the survival of this age/sex class is primarily responsible for regulating population growth and driving population trends.