Another factor to consider in release strategies is the overall risk to the population of sea otters from an oil spill. Currently, the population of sea otters in Alaska is considered a subspecies (Enhydra lutris kenyoni); one that originally extended southward through British Columbia, Washington, and Oregon (Wilson et at, 1991). Although the EVOS may have killed several thousand sea otters (Doroff et al., 1993; Garrott et al., 1993), it did not place the northern subspecies of sea otter, which numbers more than 100,000 animals (Calkins and Schneider 1985, USFWS unpublished data), at biological risk. Given the low risk to the Alaskan population and the northern subspecies as a whole, more costly and controversial release strategies to safeguard the releasable sea otters, such as long-term holding, were not necessary.
If possible, rehabilitated sea otters in Alaska should be released within the subpopulation of their origin, which increases the probability that an individual will be familiar with that area and the food types available in that area. Table 10.1 lists suggested subpopulations of sea otters in Alaska that were identified by the State of Alaska as potential management units when they requested return of management of marine mammals during the late 1970s. These areas were defined in part by the locations of remnant populations, transplant locations, and geographic considerations such as habitat discontinuities.
Sea otter populations in California, Washington, and British Columbia are discontinuous. The population in California also is afforded sub specific status (E. l. nereis) based on skull morphology (Wilson et al., 1991). Although the genetic uniqueness of the California population is unclear, preservation of that gene pool is the safest course of action, perhaps justifying more extreme measures for safeguarding rehabilitated animals if an oil spill were to occur there. Whereas rescue efforts following the EVOS had little effect on the overall population in Alaska, similar efforts expended on behalf of the southern sea otter in California could be significant, especially if a large oil spill affected their entire 300-mile range.
The range of E. l. nereis presumably extended from Morro Hermoso in Baja California, Mexico (Kenyon, 1969) north to the California-Oregon border (Wilson et al., 1991), leaving a large area of unoccupied habitat suitable for relocation if necessary. However, any attempts to relocate sea otters to northern California will be met with considerable resistance from some segments of the public because of important commercial and recreational shellfish fisheries. An oil spill in the range of the southern sea otter could create a real dilemma for releasing rehabilitated sea otters, perhaps necessitating long-term holding until the habitat is sufficiently recovered.
Sea otter populations in both Washington State and British Columbia resulted from transplants of individuals from Alaska (Jameson et al., 1982); taxonomically they belong to the northern sea otter, E. 1. kenyoni. Presumably sea otters in those locations are genetically similar to those in Alaska. If at all possible, rehabilitated sea otters from those areas should be released in coastal Washington State or British Columbia. However, the Alaska origin of those populations increases relocation options, should more extreme measures be needed. If populations in those areas were severely depleted by an oil spill, they presumably could be augmented with sea otters from Alaska. Furthermore, if Washington and British Columbia were severely affected by a large oil spill, perhaps rehabilitated sea otters from those populations could be released in Alaska.
