Polar Bears in the Deep Arctic Basin
Ovsyanikov, N. 2010. Polar bear research on Wrangel Island and in the central Arctic Basin. In, Proceedings of the 15th meeting of the Polar Bear Specialists Group IUCN/SSC, 29 June-3 July, 2009, edited by Obbard, M.E., Theimann, G.W., Peacock, E. and DeBryn, T.D., pp. 171-178. Gland, Switzerland and Cambridge UK, IUCN.
The late summer Arctic Basin surveys were split between two years, each taking a different route: the 2005 expedition surveyed northward from Wrangel Island (in the far eastern Russian Arctic), on both sides of the 180° meridian up to 79°15' N, while the 2007 trip surveyed north from Franz Joseph Land (in the far western Russian Arctic, at about 81°N, 60°E), to the North Pole and back. Observations were taken 24hrs/day from the ship bridge for the duration of the trips and sightings of both bears and ringed seals were recorded.
In 2005, 18 bears were seen north of Wrangel, 12 of these above 75°N, which marks the edge of the continental shelf at this location. Ten of the bears seen were in four family groups and three of these families were observed north of the continental shelf. All were in good physical condition. A female and her single cub-of-the-year were observed feeding on a ringed seal at 78°50.20' N, 177°27.40' W, where water depth under the ice was 1500 m. In addition, seven tracks of lone bears were recorded north of the continental shelf. A total of 48 ringed seals were observed from Wrangel Island to 79°15' N, more than half of these between 78°-79° N.
In 2007, the survey ship worked the other side of the Arctic Basin, north of Franz Joseph Land, where the continental shelf ends between 82°-83° N (Weber, 1983). Seven polar bears were sighted beyond 81° N, all of them in good condition and all recorded on fields of substantial ice. One female was observed and photographed at the North Pole on 1-2 August 2007. A total of 61 tracks of single bears were also recorded, with a concentration around 82° N. Eleven ringed seals were also observed, five between 82°-83° N, three between 83°-87° N and three between 89°-90° N (including one at the North Pole). A lower proportion of the observations of seals and bears were noted beyond the continental shelf north of Franz Joseph Land than were sighted north of Wrangel Island but a few seals and at least one bear were recorded close to, or at, the North Pole.
The deep water over the Arctic Basin is often assumed to be of such low productivity (e.g. Fischbach et al., 2007; Obbard et al., 2010) that it is largely unsuitable for polar bears except as a transit corridor. However, this assumption is contradicted by measurements of significant amounts of phytoplankton and ice algae (e.g. Gosselin et al., 1997; Stirling, 1997) as well as reports at the North Pole of "small fish" (estimated as 5-8cm, presumably young polar cod, Boreogadus saida) thrown up by ice-breakers and algal growth visible on the underside of broken ice chunks (Todd et al., 1992). Polar cod and their prey are the food of ringed seals and are known to live under ice of all types, including multi-year and first year drifting sea ice regardless of the ocean depth (Lønne and Gulliksen, 1989). The cracks ("leads") that continuously develop in moving multiyear ice allow thinner first year ice to form, creating habitat for seals and thus potential food for polar bears (Stirling, 1997).
Ovsyanikov suggests that ringed seals living at the periphery of the Arctic Ocean move into the central Arctic Basin as the pack ice recedes in late summer and that polar bears which choose to stay on the pack ice (rather than moving onto land) move along with the seals and the ice into the central Arctic beyond the continental shelves. Previous reports have also documented the presence of both ringed seals (Todd et al., 1992) and polar bears in the central Arctic Basin (Van Meurs and Splettstoesser, 2003); in 1992-93, a female tracked via satellite by Durner and Amstrup (1995) migrated from Prudhoe Bay in the southern Beaufort to northern Greenland via the central Arctic Basin (going as far north as 88°).
Ovsyanikov's Arctic Basin survey confirms that ringed seals and polar bears do not require ice that is positioned over shallow, continental shelf waters, although higher densities of both species undoubtedly exist in such areas (e.g. Derocher et al., 2004). Ovsyanikov's study, although limited, is the first systematic look at polar bears and ringed seal abundance within the Arctic Basin. Further surveys may reveal that the Arctic Basin is a more important habitat for polar bears than has been assumed (e.g. Obbard et al., 2010).
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