Chapter 4: Genetic and Historical Considerations of Oregon Sea Otters

SHORT SUMMARY:

Oregon’s sea otter population was hunted to extinction during the international maritime fur trade. The last native sea otter was killed in the early 20th century. Although sea otters probably occupied most of the Oregon Coast—evidenced by sea otter remains in archaeological sites within First Nations middens—the historical population size remains unknown. The scarcity of documentation for Oregon otters hunted during the fur trade might indicate that population density throughout the state was relatively low; however, studies using genetics to determine which sea otter subspecies, northern or southern, aligns best with Oregon’s extinct sea otter population suggest that Oregon likely represented a hybrid zone, with ancestors genetically resembling both southern and northern sea otters.

It seems clear that the successful reintroductions of sea otters to Washington, Vancouver Island, and Southeast Alaska have been instrumental in increasing population connectivity, with evidence of migrants carrying their genetic material between neighboring sea otter populations. These translocations have arguably been the most successful management tool to recover extirpated sea otter populations and their genetic diversity.

The criteria for selecting a source population for a reintroduction to Oregon should attempt to maximize genetic diversity and establish genetic consistency with Oregon’s original pre-fur trade population. Information obtained from First Nations oral histories, archaeological remains, and genetic studies suggests that Oregon represented a hybrid zone between southern and northern sea otter populations. Based on this evidence, any future reintroduction effort to Oregon should aim to recreate such a hybrid zone by using both southern and northern source populations for an Oregon reintroduction. The U.S. Fish and Wildlife Service could approve the use of northern sea otters as a source population for a northern Oregon release site and southern sea otters as a source population for a southern Oregon release site, which might allow migrants to exchange gene flow soon after reintroduction. Alternatively, an Oregon reintroduction using a northern sea otter source population and a northern California reintroduction using southern sea otters as a source population could be authorized, allowing populations to reestablish themselves in historical areas and reconnect over time. Either of these strategies could help recover genetic diversity by mixing northern and southern sea otters and restoring the potential for gene flow through the 900-mile gap in sea otter distribution that exists from central Washington to south of San Francisco.