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Pacific Walruses


by
Gerald W. Garner
National Biological Service
Figure. Distribution of Pacific walruses in the Bering and Chukchi seas of Alaska and Russia (Fay 1982).
Pacific walruses (Odobenus rosmarus divergens) live in the Bering and Chukchi seas of Alaska and Russia (Figure). The population is subject to a Native subsistence harvest in Alaska and a commercial and subsistence harvest in Russia. Total annual harvest ranges between 5,500 and 10,300 walruses (Fay et al. 1989). The Marine Mammal Protection Act requires management of the population within an optimal sustainable population range, and the subsistence harvest by Alaskan Natives cannot be regulated unless the population is declared depleted.
Pacific walruses are an important source of meat and ivory for Native peoples of Alaska and the Chukotka Peninsula, Russia. The species is long-lived, has a relatively low reproductive rate, and occupies a position near the top of the marine food chain. Thus, besides being a very visible species, the walrus may be an indicator of the health of the Arctic marine ecosystem. The United States and the former Soviet Union initiated cooperative surveys throughout the entire range of the shared population in 1975 and have since conducted periodic surveys at 5-year intervals.

U.S.-Russian Walrus Surveys
Walruses are gregarious and often form large groups when resting on sea ice or land. This behavior is called "hauling-out," and land sites where large groups traditionally congregate to rest are commonly called "haul-outs." The cooperative U.S.-Russian surveys used aerial counts of walruses on sea ice in the Russian and U.S. sectors, aerial and photographic counts at Russian land haul-outs, and ground and aerial counts at U.S. land haul-outs (Estes and Gilbert 1978; Estes and Gol'tsev 1984). Aerial surveys were conducted in the U.S. sector during 1975, 1980, and 1985, and were extended to include sea ice within the Russian sector during 1990 (Gilbert et al. 1992). Biologists altered each subsequent aerial survey to increase the precision of the estimates (Johnson et al. 1982; Gilbert 1986, 1989; Hills and Gilbert 1994).
Because of the ongoing efforts to improve the surveys, specific techniques varied among years but the basic design was to fly a series of north-south transects beginning at the edge of the polar ice pack and ending where concentration of ice was sufficient to exclude walruses. Transects were arranged systematically and stratified to achieve maximum coverage of the Chukchi Sea. Transects were located approximately between Pt. Barrow, Alaska, and the international border in 1975, 1980, and 1985, and throughout the entire Chukchi Sea during 1990. Most land haul-outs also were surveyed from aircraft, either by counts made directly by observers or from photographs. Some haul-outs were visited and counted by observers on the ground.
Biases were evident in the survey data, and lack of precision was common in all surveys (Estes and Gilbert 1978; Johnson et al. 1982; Gilbert 1989; Gilbert et al. 1992). Surveys, however, were continued because biologists believed that, despite these faults, the surveys would indicate population trends and were the best available method for assessing population size (Johnson et al. 1982; Gilbert 1986). Also, researchers recognized that an unknown and variable part of the walrus population was not available for counting because the number of walruses that were hauled out on land or ice varied significantly from day to day (Estes and Gilbert 1978; Gilbert 1989; Gilbert et al. 1992). None of these surveys used a correction factor for this unobserved fraction, and no attempts were made to classify walruses by age or sex. Even though population trends cannot yet be reliably determined by these surveys, researchers believe that long-term data from the surveys will eventually provide more definitive information about the status and trends of walrus populations.

Walrus Population Estimates
The point estimates for walrus population size were 221,000 for 1975, 246,000 for 1980, 234,000 for 1985, and 201,000 for 1990. Even though confidence intervals of these estimates were large, these estimates are considered the best information available to assess the status and trends of the Pacific walrus (Hills and Gilbert 1994). Estimates from sea ice exceeded those from land haul-outs except during 1990, when the ice pack receded much farther north and over deeper water than in most years. Because most of the large land haul-outs were in Russia, estimates there are higher than in the United States. Although these data indicate a general decline in numbers of walrus between 1975 and 1990, some biologists question the validity of this apparent decline (Hills and Gilbert 1994). Other researchers believe the population may be declining, based on various biological indices (Fay et al. 1989).
For further information:
Gerald W. Garner
National Biological Service
Alaska Science Center
1011 E. Tudor Rd.
Anchorage, AK 99503
References
Estes, J.A., and J.R. Gilbert. 1978. Evaluation of an aerial survey of Pacific walruses (Odobenus rosmarus divergens). Journal Fisheries Research Board Canada 35:1130-1140.

Estes, J.A., and V.N. Gol'tsev. 1984. Abundance and distribution of Pacific walrus, Odobenus rosmarus divergens: results of the first Soviet-American joint aerial survey, autumn 1975. Pages 67-76 in F.J. Fay and G.A. Fedoseev, eds. Soviet-American cooperative research on marine mammals. Vol. 1: Pinnipeds. National Ocean-ographic and Atmospheric Administration Tech. Rep., National Marine Fisheries Service 12.

Fay, F.H. 1982. Ecology and biology of the Pacific walrus, Odobenus rosmarus divergens Illiger. North American Fauna 74:1-279.

Fay, F.H., B.P. Kelly, and J.L. Sease. 1989. Managing the exploitation of Pacific walruses: a tragedy of delayed response and poor communication. Marine Mammal Science 5:1-16.

 Gilbert, J.R. 1986. Aerial survey of Pacific walrus in the Chukchi Sea, 1985. U.S. Fish and Wildlife Service, Anchorage, AK. 41 pp.

Gilbert, J.R. 1989. Aerial census of Pacific walruses in the Chukchi Sea, 1985. Marine Mammal Science 5:17-28.

Gilbert, J.R., G.A. Fedoseev, D. Seagars, E. Razlivalov, and A. Lachugin. 1992. Aerial census of Pacific walrus, 1990. U.S. Fish and Wildlife Service Admin. Rep. R7/MMM 92-1. 33 pp.

Hills, S., and J.R. Gilbert. 1994. Detecting Pacific walrus population trends with aerial survey--a review. Transactions of the North American Wildlife and Natural Resource Conference 59. Wildlife Management Institute, Washington, DC. In press.

Johnson, A., J. Burns, W. Dusenberry, and R. Jones. 1982. Aerial survey of Pacific walrus, 1980. U.S. Fish and Wildlife Service, Anchorage, AK. 32 pp.


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