Developing population models to examine mortality impacts and spatial components of sea otter demographics (Hosted by NCEAS)

The Southern sea otter population has recovered from near extinction over the last 100 years. The slow recovery rate in California (5% annually) compared to Alaskan populations (17-20%), suggests that the southern population is highly vulnerable to emerging mortality problems (e.g., disease) and ecological disasters (e.g., oil spills). Over the last 3-5 years, recovery of the southern sea otter population has ceased and abundance has declined. By 1999, the population declined approximately 12% from its peak in 1995. This decline has been accompanied by in apparent increase in sea otter strandings and it is generally believed that mortality is the key factor regulating southern sea otters. Studies at the National Wildlife Health Center (NWHC) and California Department of Fish and Game (CDFG) suggest that disease mortality patterns may have changed over the past 10-20 years and newly recognized diseases may pose a significant threat to sea otters. The goal of our working group is to develop demographic models to evaluate impacts of mortality on sea otter populations for both overall population growth as well as spatially explicit components. Modeling approaches will rely on a variety of data sources including abundance estimates, mortality data, and cause specific death information. We will use a maximum likelihood to evaluate changes in mortality for age and sex groups, and estimates of probability of mortality through space and time will be used to evaluate the relative contribution of each mortality source to total mortality. This modeling will set the stage for future evaluation of 1) historical changes in mortality patterns, 2) spatial relationships between disease and otter population and habitat distribution, and 3) spatial relationships between disease mortality and sources of disease agents (e.g., sewage).