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Status and Trends of Sea Otter Populations in Southeast Alaska, 1969-2003

George G. Esslinger·James L. Bodkin
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Abstract

Aerial surveys of all known sea otter (Enhydra lutris) habitat in Southeast Alaska (SE AK) in 2002-2003 indicated a population size of 8,949 otters [Standard Error (SE) = 899] at an average density of 0.92 otters per square kilometer. These findings on sea otter distribution and abundance were compared to results from several previous surveys. Sea otters have expanded their range beyond the outer coast of SE AK and currently occupy inside waters such as Glacier Bay and Sumner Strait. This range expansion, along with archeological evidence, supports the hypothesis that sea otters are capable of colonizing inside waters in SE AK. Inside Glacier Bay National Park and Preserve, in northern SE AK, sea otter abundance has increased from 5 in 1995 to 1,266 (SE = 196) in 2002, more than doubling on an average annual basis, indicating immigration and reproduction as factors contributing to population growth. In the remainder of northern SE AK, the estimated abundance has declined from 2,295 in 1987 to 1,838 (SE = 307) in 2002. In southern SE AK, the abundance of sea otters increased from 2,167 in 1988 to 5,845 (SE = 821) in 2003. Overall, population growth rates for sea otters in SE AK between 1987 and 2003 are much lower than rates from previous studies and were unexpected given the amount of unoccupied habitat available in SE AK. Divergent population trajectories were evident between the southern (6.6 percent per year) and northern areas of SE AK (2.0 percent per year). These differences suggest variation in reproductive or survival rates between the areas. Harvest levels between 1989 and 2003 may have had a measurable effect on sea otter populations in SE AK. Available data on age and sex specific fecundity and survival rates could be used to develop age- and sex-structured population matrix models to help guide management and conservation of sea otter populations.

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George G. Esslinger, James L. Bodkin. 2009. Status and Trends of Sea Otter Populations in Southeast Alaska, 1969-2003. https://doi.org/10.3133/sir20095045

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