"Alaska Ecosystems Program"

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.

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.

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.

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.

The Pribilof fur seal herd has twice demonstrated its resilience by recovering from excessive exploitation. About 40 years were required, in its most recent recovery, for the herd to increase from about 200, 000 to a near peak population estimated at 1,500, 000. Relatively simple management consisting of protecting females and killing a selected group of males on land was sufficient to permit herd recovery. The steady increase in the number of skins harvested, until about 1940, satisfied responsible officials that management, and consequently research, was adequate.

The third year of pelagic fur seal research, under the terms of Interim Convention on Conservation of North Pacific Fur Seals, was carried out in 1960 off Alaska. Two vessels, chartered by the United States for the research, worked from March to May from near Sitka into the Gulf of Alaska, in June between Kodiak and Unalaska, and in July and August from Unimak Pass to Pribilof and St. Matthews Islands, and adjacent sea area. Only one vessel operated during March and the first half of April and during July and August.

The United States began an experiment designed to obtain maximum sustainable productivity of the fur-seal resources concurrently with the drafting of the Interim Convention on Conservation of North Pacific Fur Seals.

The second year of pelagic fur seal research was carried out in 1959, under the terms of the Interim Convention on Conservation of North Pacific Fur Seals.

Reaching the objective of fur-seal research and management, maximum sustained productivity from the Pribilof, seal herd, is now complicated by acute fluctuations in the size of year classes. When the experimental approach to the calculated point of maximum yield began in 1956, year-class fluctuations were moderate, as they apparently had been since commercial sealing resumed after the Convention of 1911. These sharp fluctuations stimulated renewed emphasis on ways to forecast year-class success and, consequently, the probable size of the kill. Island seal-pup mortality, number of 2-year-old seals taken, and early season kins. of 3-year-old seals have shown some promise as indicators for making kill-size predictions. Measurements of condition or growth may be supplementary information indicative of the relative success of a year class. Recent studies suggest an inverse relationship between the return of bachelors and year-class size.

In 1958, the first pelagic research was carried out lUlder the terms of the Interim Convention on Conservation of North Pacific Fur Seals which is scheduled to last for six years.