Oil Spill polar bear interaction modelling. The polar bear is the apical predator of the arctic ecosystem and perhaps the universal symbol of the Arctic. Polar bears have long been an important subsistence resource. They also may be the most important species indicating the general health of the arctic ecosystem (Stirling and Derocher 1993). The distribution of polar bears is tied to that of sea ice. They are most common in the areas near the continental shelf where the active ice over the deep water of the polar basin meets the shallow shelf water, and where there are persistent leads and openings suited to hunting seals. The continental shelf also is one of the primary areas targeted for future oil exploration and development (Stirling 1990). Hence, the spilling of oil from offshore exploration projects could foul some of the most important foraging habitats of polar bears. Although the direction of drift in the near-shore sea ice can change almost hourly, it is predominantly and most consistently east to west. Therefore, a large spill in the eastern or central Beaufort Sea could potentially contaminate a band of polar bear habitat extending all the way into the Chukchi Sea (Stirling 1990). Spilled oil would be concentrated in pools on the ice surface and accumulate in leads and openings-at least until ablation of the annual ice in summer (Neff 1990). This mechanical concentration of spilled oil would increase the probability that polar bears and their principal prey (ringed seals, Phoca hispida) will be directly oiled. The oiling of their prey suggests bears also would be secondarily exposed to oil by consuming fouled prey. Because bears are known to consume foods (and non-food items) fouled with petroleum products, and because they groom intensively when their fur and environment are fouled, we can expect that any large spill in the ice environment will result in contaminated polar bears. Fortunately, there have been no marine oil spills in the 25+ years of arctic exploration and development. Nonetheless, oil and other chemicals can be fatal to exposed bears (Oritsland et al. 1981, Amstrup et al. 1989, St. Aubin 1990). There have as yet been no attempts to project the mortality that could be caused by oil spills. Without such projections, management responses to spills, if they should occur, will be inadequate. Specific objectives of this project are to: 1. Predict number and distribution of polar bears that may be exposed to a variety of oil spill scenarios. 2. Predict the number and distribution of polar bears that would be killed by each spill scenario. 3. Predict the time necessary for the population to recover to its pre-spill levels. The strategy for meeting the above objectives is to link existing USGS Alaska Science Center - Biological Science Office data on polar bears with data and models describing the hypothetical behavior of oil that might be spilled at various locations in the Beaufort Sea. Conceptually, data on the movements and distribution of polar bears would be converted into estimates of seasonal density at any place within the occupied range of polar bears. Polar bear density estimates would then be overlain (using GIS software) by hypothetical oil drift and distribution scenarios. The overlap between polar bear coverages and oil spill coverages would be used to estimate numbers of bears that might be oiled in each scenario. Of bears exposed to oil, we would estimate proportions whose exposure might be fatal. Finally, we would use existing population dynamics data on polar bears in the Beaufort Sea to predict the post-spill recovery of the population. The ASC-BSO will have the lead on the density estimation and population modeling phases of this project. MMS will develop oil-spill trajectories.