Management of northern fur seals on the Pribilof Islands, Alaska, 1786-1981

Abstract

This paper includes information about the Pribilof Islands since their discovery by Russia in 1786 and the population of northern fur seals, Cailorhinus ursinus, that return there each summer to bear young and to breed. Russia exterminated the native population of sea Oilers, Enhydra lulris, here and nearly subjected the northern fur seal to the same fate before providing proper protection. The northern fur seal was twice more exposed to extinctionfollowing the purchase of Alaska and the Pribilof Islands by the United States in 1867. Excessive harvesting wasstopped as a result of strict management by the United States of the animals while on land and a treaty betweenJapan, Russia, Great Britain (for Canada), and the United States that provided needed protection at sea. In 1941,Japan abrogated this treaty which was replaced by a provisional agreement between Canada and the United Statesthat protected the fur seals in the eastern North Pacific Ocean. Japan, the U.S.S.R., Canada, and the United Statesagain insured the survival of these animals with ratification in 1957 of the "Interim Convention on the Conservation of North Pacific Fur Seals," which is still in force. Under the auspices of this Convention, the United States launched an unprecedented manipulation of the resource through controlled removal during 1956-68 of over 300,000 females considered surplus. The biological rationale for the reduction was that production of fewer pups would result in a higher pregnancy rate and increased survival, which would, in turn, produce a sustained annual harvest of 55,000-60,000 males and 10,000-30,000 females.Predicted results did not occur. The herd reduction program instead coincided with the beginning of a decline in the number of males available for harvest. Suspected but unproven causes were changes in the toll normally accounted for by predation, disease, adverse weather, and hookworms. Depletion of the animals' food supply by foreign fishing Heets and the entanglement of fur seals in trawl webbing and other debris discarded at sea became a prime suspect in altering the average annual harvest of males on the Pribilof Islands from 71,500 (1940-56) to 40,000 (1957-59) to 36,000 (1960) to 82,000 (1961) and to 27,347 (1972-81). Thus was born the concept of a research control area for fur seals, which was agreed upon by members of the Convention in 1973 and instituted by the United Stateson St. George Island beginning in 1974. All commercial harvesting of fur seals was stopped on St. George Islandand intensive behavioral studies were begun on the now unharvested population as it responds to the moratoriumand attempts to reach its natural ceiling. The results of these and other studies here and on St. Paul Island areexpected to eventually permit a comparison between the dynamics of unharvested and harvested populations, which should in turn permit more precise management of fur seals as nations continue to exploit the marine resources of the North Pacific Ocean and Bering Sea. (PDF file contains 32 pages.)