Estimates of carrying capacity for sea otters in Washington state

We obtained index estimates of carrying capacity W for the Washington sea otter (Enhydra lutris kenyoni) population as products of the density of sea otters at equilibrium within a portion of their existing range and the total amount of available habitat. We classified sea otter habitat as rocky, sandy, or mixed during aerial surveys along the Washington coast in March 2000. We characterized substrate type and kelp composition from the coast to the 40-m depth contour and computed area (km(2)) and available coastline (km) within each habitat. We calculated maximum foraging depths and maximum distance from shore for 68 sea otters radiotagged between 1994 and 1998 and used the estimites to approximate the offshore extent of sea otter habitat. We used the most current population survey data (1996-1999) to obtain equilibrium densities of sea otters in rocky habitat in Washington. Because sea otters have only recently occupied sandy or mixed sites, the equilibrium densities for these habitats represent a proportional density, based on current counts in the rocky equilibrium region in Washington and available data from the California sea otter population. Index estimates of K for the Washington sea otter population range from 1,372 (CV 0.13) to 2,734 (CV 0.13). These estimates are useful for sea otter management because they directly relate to the index counts Used to monitor the population since 1977. Our results will facilitate decision-making by entrusted management agencies regarding stock assessment and population status under the United States Marine Mammal Protection Act.