Oiled Sea Otter Rehabilitation Course

Selection of Release Sites

Sharpe (1990) described criteria that were used to evaluate release sites along the Kenai Peninsula for sea otters following the EVOS. These criteria included:

1) amount of habitat of shallow or moderate water depth,
2) amount of kelp,
3) amount of weather-protected habitat,
4) water quality,
5) distance from oiled areas,
6) suitability for post release monitoring,
7) number of sea otters already occupying the area, and
8) suitable transfer sites (helicopter landing zones).

These are reasonable criteria for evaluating specific release sites. Amount of kelp was used by Sharpe (1990) as an indicator of habitat productivity, but in many areas an abundance of kelp does not necessarily equate with abundant food resources for sea otters. Kelp may be uncommon in some coastal areas of Alaska, especially those dominated by soft bottoms in which bivalves make up the predominant foods of sea otters. Moreover, in some rocky areas, abundant kelp is a reliable indicator of heavy and persistent feeding by sea otters (VanBlaricom and Estes, 1988).

Obviously, the presence of other sea otters may be the best indicator that a particular habitat is suitable for sea otters. However, uncertainties associated with disruption of the social organization of otters already in the area may be an important consideration. In addition, placement of sea otters in an unfamiliar area may place them at a competitive disadvantage with local sea otters.

Through predation, sea otters are rapidly able to affect the quantity and size of sessile or slow-moving shellfish. Therefore, the only way to assure that food is not limiting to rehabilitated sea otters is to release them in unoccupied or recently occupied areas. However, as discussed above, this strategy will likely be met with considerable resistance by commercial, subsistence, and recreational fishermen who use the same resources as sea otters.

Prerelease intertidal and subtidal surveys in occupied habitats can reveal on a gross scale the relative abundance of prey in an area. However, because of the patchy nature of their food resources and the ability of healthy sea otters to thrive in areas of long-standing occupation where food appears limited, surveys undertaken to assess the abundance of food resources at potential release sites may be difficult to interpret.

Given the resolution of most habitat studies, it is unlikely that pre- and postrelease habitat surveys will be able to document any effects of the released animals on the abundance of sea otter prey.

Recent studies suggest that individual sea otters specialize in certain kinds of prey within a given habitat (M. Riedman, Monterey Bay Aquarium, personal communication; K. Lyons, University of California, personal communication). Therefore, it may be advisable to release sea otters in areas that contain populations of prey comparable to those from where they were captured.

The effect of releasing rehabilitated sea otters on the wild population is not known. Sea otters are gregarious animals with a complex social organization (Garshelis et al., 1984; Riedman and Estes, 1990). Although their social organization has been described in general terms, little is known about the importance of the social bonding that exists outside of mating and between mothers and pups. Capture, treatment, and temporary holding of sea otters undoubtedly are very disruptive to their social organization. Release of those sea otters may also cause stress depending on the release strategy. Relocating sea otters to an already inhabited area may disrupt both the rehabilitated animals and the receiving population.