Threatened and Endangered Species - Status Reports
Date Published: July 1993
Number of Pages: 122
On 5 April 1990, the National Marine Fisheries Service published an emergency rule listing the Steller (northern) sea lion (Eumetopias jubatus) as a threatened species under provisions of the Endangered Species Act. Final listing for the species became effective on 4 December 1990. The listing action was deemed appropriate because of a major, rapid decline in ·sea lion numbers that had occurred throughout most of Alaska, within the core of the species' range. Counts of juveniles and adults in the region from the Kenai Peninsula to Kiska Island (i.e., the central and western Gulf of Alaska, and the eastern and Central Aleutian Islands) declined 63% between 1985 and 1989. In addition, counts from trend sites (rookeries and haulouts that have been counted during every major survey) between the late 1950's and 1990 showed an overall decline of 78%.
The reasons for the decline are not well understood. Changes in the quantity or quality of available prey may have contributed to the decline. Evidence of major shifts in the abundance of fish in the Bering Sea over the past several decades is well documented. Estimates of abundance of walleye pollock increased significantly in the late 1970's. This and other important sea lion prey support a major commercial fishery and millions of metric tons are removed by the fishery each year. The development and expansion of commercial fisheries throughout the sea lion's range may have caused detrimental changes in the food supply. However, the complexity of ecosystem interactions, and limitations of data and models make it difficult to determine how fishery removals may have influenced the population.
In the past, Steller sea lions have been harvested commercially and this may have contributed to decline over the past 30 years. A total of 45, 178 pups were killed in the eastern Aleutian islands and Gulf of Alaska between 1963 and 1972. An experimental harvest in 1959 resulted in 616 adult males being taken. While this harvest may have been significant to some of the decline, it does not explain why numbers declined in areas that were not harvested or why declines in some areas were most pronounced 20 years after the harvest. Sea lion losses incidental to commercial fisheries may also have contributed to the overall decline. The total estimated incidental catch of Steller sea lions in foreign and joint-venture trawl fisheries was over 20,000 animals for the period. 1966- 1988. A variety of other factors, including disease, contaminants, El Nino events (warmwater currents), and subsistence harvest by Alaska natives are considered either unimportant or too poorly understood to be considered meaningful to the observed decline.
In Washington, Steller sea lions are present year-round but are most abundant during fall and winter. They occur in greatest abundance along the outer coast from Cape Flattery to the mouth of the Columbia River. Some individuals also occur in inland waters such as Puget Sound. More than 1,000 animals of all age and sex classes have been counted during surveys in recen t years. Although breeding sites for this species occur in British Columbia, Oregon, and northern California, breeding was not documented in Washington until 1992 when a single pup was born on Carroll Island.
The National Marine Fisheries Service has listed the Steller sea lion as threatened throughout its range and Washington's Steller sea lions are part of the threatened population. Recovery actions are needed to correct the downward population trend and have been outlined in the federal recovery plan. The Steller sea lion is not considered in immediate danger of extirpation from Washington and is therefore not recommended for endangered status. It is recommended that the Steller sea lion be designated as a threatened species in Washington.
Washington Department of Wildlife. 1993. Status of the Steller (northern) sea lion (Eumotopias juhatus) in Washington. Unpubl. Rep. Wash. Dept. Wildl., Olympia.