Decline of Steller Sea Lion Population Since 1980, the world population of Steller sea lions (Eumetopias jubatus) has dropped from around 300,000 animals to fewer than 100,000, and it is still declining. In 1997, the portion of the population breeding from Prince William Sound through the Aleutian Islands was declared an endangered species under the United States Endangered Species Act. No one knows exactly why the population is dwindling, but researchers at the North Pacific Universities Marine Mammal Research Consortium are trying to solve this mysterious puzzle.
Reasons for Population Decline Noticeable reductions or depletions have occurred in the abundance of Steller sea lion, harbour seal, northern fur seal and some sea bird populations in the Gulf of Alaska and Bering Sea. Possible causes include increased incidence of parasites and disease, predation by killer whales, 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. Other factors that may be contributing to the population decline include meteorological changes (i.e., frequency of storms), pollution and toxic substances, entanglement in marine debris, and incidental and intentional take by man.
For the most part, data to assess each of the possibilities are currently limited. Whether the decline is caused by a single factor or a combination of all of the above is a matter of scientific debate. Research by the Consortium, however, is focusing on the nutritional stress hypothesis as a major contributor to the population decline.
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