Oiled Sea Otter Capture Course

A Brief Historical Perspective


The past four decades have seen at least twenty-nine encounters between pinnipeds and oil (St. Aubin, 1990a), although these have resulted in too few quantitative accounts to allow us to accurately predict the impact. Large scale mortality has rarely been observed, but oil has clearly been implicated in some deaths.

Many of the reports have been anecdotal and do not specify the number of animals or species involved. Despite large numbers of seals being affected, such as 10,000-15,000 harp seals in the Gulf of St. Lawrence in 1969 (Warner, 1969) and approximately 650 gray and harbor seals following the Arrow oil spill in Chedabucto Bay in 1970 (Anonymous, 1971), little, if any, follow-up work has been done that quantitatively links mortality in marine mammals with exposure to spilled oil. An exception to this is the behavioral, histological, and toxicological study of pinnipeds following the Exxon Valdez oil spill (EVOS) (Loughlin, 1994).

Still less is known about the best approach to deal with oiled pinnipeds. Indeed, in one small study conducted on oiled gray seals on the coast of Wales in 1974, the authors concluded that the disturbance caused by cleaning was probably more damaging to the pups’ chances of survival than the oil itself (Davis and Anderson, 1976). During the EVOS, eighteen harbor seal pups were brought to rehabilitation centers in Alaska for cleaning. Although covered with crude oil, few medical problems were encountered and the seals were eventually released (Williams and Davis, 1990). In view of this, wildlife experts questioned the relative benefits of placing oiled seal pups in rehabilitation centers when important maternal bonds are broken (Williams et aI., 1994).

Laboratory studies on the effects of oil have been conducted only on ringed and harp seals (Smith and Geraci, 1975; Geraci and Smith, 1976). Such experiments are limited by public attitudes that consider them inhumane and unnecessary, and studies have been restricted to small sample sizes. Furthermore, the results of laboratory studies may be biased by stress associated with handling and captivity.

Most species of pinnipeds are sufficiently dispersed and their populations robust enough to preclude devastation by a single oiling event. Yet some, such as the Mediterranean monk seal, could be significantly affected. Their declining population of less than 1000 animals exists as several localized stocks that are highly vulnerable to oil. It is therefore imperative to gain experience while dealing with less threatened species to direct treatment of those that are most at risk.

Polar bears

The literature offers no information on the fate of bears exposed to oil in their natural environment (St. Aubin, 1990b). No major spill has occurred when bears have been present, and there are only anecdotal accounts of bears biting cans of oil or fuel storage bladders, without obvious immediate effect. Nevertheless, opportunities for contact exist throughout most of the polar bear’s range, where petroleum resources are being exploited and oil is transported and stored. Their life history and behavior also conspire to draw polar bears into contact with oil (Stirling, 1990), and it is conceivable that field workers might yet have to deal with a dozen or more bears fouled after encountering a contaminated lead.

River Otters

River otters that frequent marine habitats have been involved in several recent oil spills. This species appears vulnerable to the direct effects of oil exposure, as well as indirect effects associated with habitat contamination. The impact of oil on this species may be underestimated because river otters often return to holts following contamination.

In 1978 following a spill of Bunker C fuel from the Esso Bemicia, fourteen carcasses and eighteen live oiled otters from a population of European river otters (Lutra lutra) in the Shetlands were found (Richardson, 1979). Necropsy examination of five oiled carcasses revealed congested lungs, hemorrhagic gastroenteropathy, and a mixture of oil and blood in the intestines resulting from ingestion of oil during grooming (Baker et al., 1981). In comparison, no river otter deaths could be directly attributed to oil during the 1993 Braer spill, which also occurred along the Shetland coastline a. Conroy, Institute of Terrestrial Ecology, Banchory Research Station, Scotland, personal communication). Long-term studies concerning the chronic effects of this spill are currently being conducted.

Behavioral and physiological effects have been reported for river otters (Lutra canadensis) within the spill area of the EVOS. River otters from contaminated sites showed: 1) an increase in plasma haptoglobin (an indicator of physiological stress), 2) a decrease in body mass, 3) larger home ranges, and 4) a more restricted diet than otters living in uncontaminated areas (Bowyer et al., 1993; Duffy et al., 1993). Oil related mortality and population differences between contaminated and noncontaminated sites were considered, but could not be determined due to the relatively small sample size of the studies (W. Testa, University of Alaska, personal communication).