Science & Data

This report gives the results of the fourth of six years of pelagic fur seal research to be conducted by the United States according to the Schedule of the Interim Convention on Conservation of North Pacific Fur Seals.

Beginning in 1956 the Pribilof seal herd has been subjected to a program designed to reduce the number of pups produced annually with the expectation that as the number was reduced the rate of survival would improve.

In the 4 years, 1958-61, pelagic research on fur seals as specified by the Interim Convention on Conservation of North Pacific Fur Seals carried U.S. Investigators into the entire north-to-south range of the northern fur seal in the eastern Pacific. Collecting efforts in these years were concentrated primarily where seals were abundant.

The fur seal populations in the North Pacific seem to be almost ideal subjects for testing population principles among large mammals. A large part of the population is present at one time on small islands, there is an intensive harvest, and the seals can be marked and measured. Further, there is good communication between biologists of different countries working on the different islands and at sea.

This report furnished information on the sixth year of Pelagic research on fur seals conducted by the United States as specified by the Interim Convention on Conservation of North Pacific Fur Seals.

Complete protection of female seals was one of the principles followed in restoring the reduced Pribilof seal population, after signing of the Fur Seal Convention of 1911. The steady growth of the population from 1911 to about 1940 illustrated the effectiveness of this principle. After 1940 the failure of the kill of males and the number of harem bulls to increase raised doubts about the population figures in use and the wisdom of continuing current management methods indefinitely.

This report contains information on the seventh year of pelagic fur seal research by the United States under the Interim Convention on Conservation of North Pacific Fur Seals. The first of two phases of the investigation in 1964 was on the distribution, abundance, migration, and feeding habits of fur seals off California, Oregon, and Washington in April and May; the second was on the occurrence and feeding of fur seals in Bering Sea in July, August, and early September. Reproductive condition of females was also studied.

Two recent advances in research are important for the management of fur seals (Callorhinus ursinus ) on the Pribilof Islands. First, we are making better estimates of the number of pups born, the number of females required to bear these pups, and the number of females needed each year to replace those that die. Second, we are studying the value of finished sealskins by age and sex.

Annually the Bureau of Commercial Fisheries reports on its fur seal investigations on the Pribilof Islands and at sea. Investigations on the islands are directed mainly toward the development of a rational system for holding the seal population at the level of maximum productivity. At sea, the primary motivations for research are the problems of fur seal predation on commercially important fish and the intermingling of seals from the eastern and western Pacific Ocean. It is unlikely that unequivocal conclusions can be reached soon on either problem. General understanding of the pelagic life of fur seals, however, has been greatly improved during the past 9 years of research.

The problems of managing international resources have collectively been the strongest influence in establishing and maintaining a sustained research program for the northern fur seal. Investigations intended to supply information needed by the North Pacific Fur Seal Commission for management of fur seals have continued since 1956 on the Pribilof Islands and since 1958 at sea.