The Steller sea lion Problem
Since 1980, the world population of Steller sea lions (Eumetopias jubatus), has dropped from more than 300,000 animals to fewer than 100,000. The portion of the population breeding from Prince William Sound west through the Aleutian Islands has suffered the most dramatic decline, losing 75 per cent of its numbers. In 1997, the western population was declared endangered under the United States Endangered Species Act, while the eastern Alaska population was considered threatened. Alaskan harbour seal populations have also declined, northern fur seals are depleted and similar declines have been reported in some seabird breeding colonies. In British Columbia, Steller sea lion numbers appear stable, but harbour seal populations have increased rapidly. Further south, striking increases are being observed in the range and abundance of elephant seals and California sea lions. Possible reasons for these changes include parasites and disease, killer whale predation, nutritional stress through competition with man or other species for food, or nutritional stress caused by natural and/or human-induced changes in the abundance, quality and distribution of prey. Climate change, pollution, entanglement in marine debris, and incidental and intentional take by man may also be involved. Whether the decline is caused by a single factor or a combination of all of the above is a matter of scientific debate. However, the nutritional stress hypothesis is receiving increasing amounts of attention and funding in recent years. |
