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AFSC Historical Corner:  Pinnipeds and Other Marine Mammal Research

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Steller Sea Lions

Steller sea lion underwater
Steller sea lion underwater.  AFSC photo.

Ranging from California to Japan across the North Pacific Ocean, the eastern and western stocks of Steller sea lions are the largest of the eared seals, gathering to breed at over 40 rookeries. They were named after Georg Wilhelm Steller, who first described the species in 1741. Subsistence harvesting of the Steller sea lion have provided food, clothing, and skins for sea kayaks. In the 1800s, the whiskers were sold as tobacco-pipe cleaners.

Research on the species increased during the late 1900s. From 1976-90 the western stock of Steller sea lions declined in numbers, believed to have been brought about by contributing factors such as incidental take in fisheries, poaching, diseases, predation, and indirectly from fishing and climate change. Consequently, the Steller sea lion was listed as threatened under the Endangered Species Act in April 1990 and declared endangered seven years later. After a slow recovery in their population since the 1980s, the species was relisted as threatened.

NOTE:  This page is under development, pending additional content.

Event items:

  • Sea lion census, 1977

    "The northern or Steller sea lion is the most abundant sea lion in North America, estimated at 200,000 animals, ranging from off California northward into the Bering Sea. The greatest number of these animals occurs from the Gulf of Alaska to the western limits of the Aleutian Islands.

    Few comprehensive studies of abundance and distribution have been conducted on this species, especially on the Aleutian Islands. The eastern Aleutian Islands have been surveyed five times since the late 1950s. Estimates of abundance have ranged from 45,000 to 50,000 during the earlier studies to less than 25,000 in recent years.

    Because of proposed action to return management of this species to the State of Alaska and because of pending oil and gas exploration on the continental shelf near the Aleutian Islands, a population study was initiated 1975 to more effectively evaluate the status of the stock.

    From June 1975 to July 1977, six aerial surveys were conducted, along the eastern Aleutian Islands and north coast of the Alaska Peninsula to determine the distribution and abundance of the northern sea lion. Counts of sea lions on rookeries and haul-out sites were-compared with counts made in 1957, 1960, 1965, and 1968.

    When these data were rigorously compared to counts from 1975 to l977, a chronological population decline of 40 to 50% over the past 20 years was evident. Factors which may have contributed to the decline are (1) a westwardly shift in distribution, (2) an increase in fisheries interactions in the survey area, (3) removal of pups during commercial harvest, and (4) an, as yet, unidentified population controlling factor."  (From Northwest and Alaska Fisheries Center Monthly Report, Dec. 1977).

  • Marmot Island northern sea lion research: June 1988 preliminary results

    Members of the National Marine Mammals Laboratory (NMML) conducted field studies of northern sea lions, Eumetopias Jubatus, at Marmot Island, Alaska, 20 June to 6 July 1988. This research was a continuation of work initiated in 1987 to assess the trend in abundance of northern sea lion populations and to devise methods for determining the cause of observed population declines. NMML staff were joined by two scientists from the Soviet Union, Dr. V. Vladimirov (VINRO, Moscow) and Mr. V. Shevljagin (Glavrybvod, Moscow). The cooperative involvement by the Soviet scientists was made possible by a grant from the Trust for Mutual Understanding and administered through the U.S. Department of Interior as part of the U.S.-U.S.S.R. Cooperative Program on Protection of the Environment.

    The principal research objectives on Marmot Island were to 1) count the number of live pups, juveniles, and adult sea lions by sex at each beach; 2) test the effectiveness of Telazol as an anesthetic for sea lions and attach radio transmitters to anesthetized animals; and 3) apply brands and flipper tags to pups for long-term survival studies, and monitor animals tagged during 1987.

    A total of 3,136 live pups were counted, approximately 200 more than in 1987. NMML staff did not count dead pups during the live pup count since the number of dead pups on the beach at time has no meaning to the overall number of pups that may have died. Dead pups frequently are washed off beaches during tidal cycles or are removed by eagles, foxes, or other scavengers. Field crew members visited all rookeries and haul-out sites on 29 June and using binoculars and spotting scopes counted adult and juvenile animals. The count total was 3,206 sea lions which included 2,221 females, 155 territorial males, 321 other males, and 509 juveniles and "others." The count was less than in 1987 on 13 - June (3,788) and 3 July (3,335), but these differences could be accounted for by varying daily haul-out patterns. Nevertheless, a significant decline in numbers of adults and juveniles has occurred since 1985 (4,9813 sea lions) and 1979 (6,381).   (From Northwest and Alaska Fisheries Quarterly Report, Apr.-June 1988). 

Additional reading

  • Harry, G. Y., Jr. 1982. Marine Mammal Research. In R. R. Mitsuoka, R. E. Pearson, L. J. Rutledge, and S. Waterman (editors), Fifty Years of Cooperation and Commitment: 1931-81, the Northwest and Alaska Fisheries Center, p. 63-80. U.S. Dep. Commer., NOAA Tech. Memo. NMFS F/NWC-34.  (.pdf, 2.03 MB).
  • Kroon, C. 1984. National Marine Mammal Laboratory (U.S. DOC/NOAA/NMFS/NWAFC). Roots of Public Administration, D. Mills. 11 p.   (.pdf, 4.73 MB).
  • Marine Mammal Protection Act (1972).  ("NOAA Celebrates 200 Years of Science, Service, and Stewardship" website)

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