Island Setting

The Pribilof Islands comprise a five-island archipelago lying in the southeastern Bering Sea. While a myriad of wildlife inhabits the islands and the surrounding sea, only the two largest islands of the archipelago, St. George and St. Paul, have established human populations. The following pages describe the Pribilof Islands’ unique setting in the Bering Sea.

Map of Bering Sea
The Location of the Pribilof Islands in the Bering Sea (NOAA).
Click on the image to view a larger map.

Geology and Oceanography

The Bering Sea is a semi-enclosed sea bounded on the north and west by Russia, on the east by mainland Alaska, and on the south by the Aleutian-Commander archipelago. A deep basin (maximum depth 3,500 meters (m)) and continental shelves (<200 m deep) comprise the sea (Stabeno et al. 1999a; Winer 2001, 4–7). The sea’s eastern continental shelf is broad, measuring more than 500 kilometers (km) (Stabeno et al. 1999a). The Pribilof Islands are located on the seaward edge of the eastern continental shelf.

To the north, the Bering Sea is connected with the Chukchi Sea and Arctic Ocean through the Bering Strait. In the south, numerous passes, or straits, through the Aleutian-Commander archipelago connect the Bering Sea with the Pacific Ocean (Pavlov and Pavlov 1996). Circulation is strongly influenced by the Alaskan Stream, which enters the Bering Sea through the many passes. The inflow into the Bering Sea is balanced by outflow through Kamchatka Strait. Circulation in the Bering Sea is often described as a cyclonic gyre, with the southward flowing Kamchatka Current forming the western boundary current and the northward flowing Bering Slope Current forming the eastern boundary current (Stabeno et al. 1999a). Around the Pribilof Islands, the current flows clockwise (Stabeno et al. 1999b).

Map of Bering Sea.
Map of Bering Sea Circulation (NOAA).
Click on the image to view a larger map.

Humans and Bering Sea Resources

Black and white photo of salmon drying on racks.
Salmon drying on racks at Unalaska, 1888 (NARA).

The Bering Sea region sustains over 100,000 people, including the Aleut, Yup’ik, Cup’ik, and Inupiat peoples living on Alaska’s coasts and islands; and the Aleut, Yup’ik, and Chukchi peoples living on Russia’s coasts and islands (WWF and TNC 1999). The region is also a seasonal or year-round home to some of the world’s largest marine mammal, bird, fish, and invertebrate populations, and supports some of the world’s largest commercial harvests of seafood, including groundfish, cod, pollock, salmon, and crabs (Loughlin et al. 1999).

The history of interactions between humans and resources of the Bering Sea stretches back thousands of years and can be separated into four distinct, though overlapping, periods (Loughlin and Jones 1984). The first period is subsistence hunting by Natives, dating from circa (ca.) 28,000 years ago to present. The second period is the commercial harvest of northern fur seals, dating from 1786 to 1984. The third period is the commercial harvest of whales and walruses, dating from 1845 to ca. 1914. The fourth period is the commercial harvest of fish and shellfish, dating from ca. 1952 to present.

Bering Sea Fisheries

Graph of biomass by year.
Easting Bering Sea crab abundances (Boldt 2005, Appendix C).

The domestic Bering Sea groundfish fishery is an important segment of the U.S. fishing industry. With a total catch of two million metric tons and an ex-vessel value of $469 million in 2004 (Hiatt 2005), it accounted for 45% of the weight and 13% of the ex-vessel value of the total United States domestic landings reported in 2004 (Pritchard 2005). The groundfish fishery includes pollock, Pacific cod, sablefish, Atka mackerel, flatfish, and rockfish as target species. Halibut is managed as a separate fishery by the International Halibut Commission.

Bottom-trawl survey data from 1982 to 2004 indicates total catch per unit effort of all fish and invertebrate taxa in the eastern Bering Sea has undergone substantial variation, peaking in 1994 (Boldt 2005, Appendix C). Data for eastern Bering Sea crab abundances show a general decline from 1991 to 2004, and 2004 abundances were low relative to historic peaks (Boldt 2005, Figure 2). Of the six managed crab fisheries, three are open, three are closed, and four are at overfished levels. Rebuilding plans are in place for all overfished crab stocks. No Bering Sea/Aleutian Island groundfish stock is considered overfished or subject to overfishing, nor is halibut considered subject to overfishing.1

Marine Mammals

Photo of a group of seals on rocks.
A harem of northern fur seals (NOAA).

Twenty-five marine mammal species are present in the Bering Sea from the orders Pinnipedia (sea lions, walrus, and seals), Carnivora (sea otter), and Cetacea (whales, dolphins, porpoises) (Loughlin et al. 1999). The western stock of Steller sea lions (Eumetopias jubatus), found west of 144° longitude, has been listed as endangered under the Endangered Species Act since 1997. After being hunted to near-extinction during the eighteenth and nineteenth centuries, sea otters (Enhydra lutris) have repopulated their original habitat from Attu to the southeastern part of Alaska thanks to strict protection and careful management (Haley 1986). Although the abundance of most whales and dolphins in the Bering Sea is low, primarily because this is the northern extent of their ranges (Loughlin et al. 1999), approximately 50% of the world’s northern fur seal (Callorhinus ursinus) population breeds and gives birth on the Pribilof Islands (Testa 2005).

Seabirds

Photo of black and white birds sitting on rocks.
Thick-billed murres on the cliffs of St. George Island (NOAA).

Thirty-eight species of seabirds inhabit the Bering Sea and adjacent waters (Loughlin et al. 1999). This includes the Procellariiformes (albatrosses, shearwaters, and petrels), Pelecaniformes (cormorants), and two families of the Charadriiformes—Laridae (gulls) and Alcidae (auks, such as puffins, murres, auklets, and murrelets). The National Marine Fisheries Service and the U.S. Fish and Wildlife Service estimate that seabird breeding populations in the Bering Sea number thirty-six million (Boldt 2005, Appendix C).

View a video of seabirds on St. George Island

View a video of seabird research activities

Role of Sea Ice

The presence of sea ice in the Bering Sea is significant. It plays an important role in the timing of the spring phytoplankton bloom, which in turn has impacts on benthic and pelagic communities (Stabeno and Overland 2001). It has also provided a hunting and transport platform to walrus, polar bears, and Alaska Natives. It is assumed Arctic foxes (Alopex lagopus) originally made their way to the Pribilof Islands by sea ice (Preble and McAtee 1923, 104–105), and local residents have reported foxes using sea ice to move between islands in modern times. Government log books for the Pribilof Islands indicate polar bears, not normally found on the islands, have occasionally arrived and left by ice.2

Photo of snow and sea ice.
Sea ice in the Bering Sea, March 1979 (NOAA).
Graph showing sea ice concentration per year.
Concentration (% cover) of sea ice over the southeastern Bering Sea between latitudes 57o North and 58o North (NOAA).

Prevailing winds advect sea ice southward in the Bering Sea (Stabeno and Overland 2001). The presence of sea ice influences water properties and the vertical structure of the water column (Stabeno et al. 1999b). The amount of seasonal sea ice is a defining characteristic of winter on the eastern continental shelf, and the degree of sea ice cover is an indicator of environmental conditions that will persist from winter through summer (Wyllie-Echeverria and Ohtani 1999). The residence time index (RTI) and the seasonal sea ice index (SSII) are two methods of indexing seasonal sea ice cover in the Bering Sea. RTI reflects the duration of ice each year in a gridded area. SSII is the southernmost position of sea ice along longitude 169° west. Both models show inter-annual and multi-annual variability between heavy and light ice cover, including a shift from heavy ice cover pre-1977 to lighter ice cover (Wyllie-Echeverria and Ohtani 1999). In 1989, the Arctic Oscillation (a phenomenon associated with the polar vortex) changed, and ice coverage slightly increased though it did not return to the cold years of the early 1970s (Stabeno and Overland 2001). Beginning in 2000, a marked decrease in ice cover occurred, with a near absence of sea ice over the southeastern Bering Sea (Overland and Stabeno 2004). During 2005, 2006, 2007, and 2008 sea ice surrounded St. Paul Island. During 2007 and 2008 it reached St. George Island .