Polar Bears, Ursus maratimus, feed mainly on ringed seal pups. These pups are usually born in early April. By the time these pups are weaned they are fifty percent fat by weight. With such a high fat content the ringed seal pups represent a high return for the energy expended by the polar bears in hunting. Until the ice breaks up these pups are abundant and easy to catch (Johannessen, 1995). Polar bears become inactive and fast when the seals are less accessible. This usually occurs in the open water season or in inclimate weather (Latour, 1981).

This mean that successful hunting in the spring allows polar bears to maximize their body reserves for periods when food is harder to come by. The large body reserves built p by the polar bears are used for survival, reproduction, and for the nursing of their cubs.

The hypothesis is that earlier sea ice breakup is the cause of the decline in physical and reproductive parameters. Because of the polar bears’ dependence on the availability of seal pups; the distribution and duration of sea ice influences the population ecology of the polar bears by influencing the access to seal pups. The timing of sea ice breakup is influences by climactic changes (McCormick, 1995).

The areas of study were the management boundaries for the Western Hudson Bay (WHB) polar bear population.

The time of sea ice breakup was estimated using regional ice analysis produced by the Canadian Ice Service. The breakup date for the ice was determined when 5/10 coverage during the period of ice melting. Conversely, the freeze up date was determined by ice coverage of 5/10 during the period of ice formation (Cloersen, 1991).

Satellite collars tracked 41 Females. Their mean dates ashore were estimated by their location in the area. In order to determine if the timing of sea ice break up was influencing the mean dates ashore; these dates were plotted against the date of ice breakup.

The condition of the bears was determined by nonselective capture. The length and weight of each immobilized bear was taken. These measurements were used in the formulate C=weight/length². C stands for the index of condition and was used so that the conditions of the bears could be compared.

The survival of cubs of the first six months was also noted in this study. Four to twenty female polar bears were tracked in February and March. Six months later the surviving cubs were counted. One thing that is unique to this population of cubs is that some do not stay with their mothers for two and a half years as do other polar bear cubs. The yearlings caught alone were also noted in this study, as the environment may be an influencing factor (Ferguson, 2000).

Forty-one female polar bears were fitted with radio collars in order to track their movements in and around a specified study area from 1991-1998. Satellite information recorded 1620 locations of bears on the sea ice during this time. 1146 (70.7%) of these locations were found in the specified study area. The other 475 (29.3%) were outside the study area.

Statistical analysis was then computed on the timing of ice break up in the study area, yielding, r=-.413; df=19; p=0.07. At a significance value of p=0.05, these results indicated an over all trend that approached significance for ice break up at an earlier date.

A correlation between the mean date on which female bears came ashore and the timing of ice break up in the study area yielded, r=0.957, df=7, p< 0.001. At a significance value of p=0.05, these results were highly significant. So significant that the range in which the bears came ashore was only between 21-28 days after significant ice break up.

Statistical analysis done on the condition of male and female polar bears and natality from 1981-1997 yielded:

Males à r=-0.732; n=17; p< 0.001

Femalesà r=-0.799; n=17; p< 0.001

Natality à r=-0.543; n=17; p< 0.05

At the significance value of p=0.05, all of these results indicated significantly declining trends.

Cub survival was recorded form 1981-1997. The results varied from 60-65% survival in the early 80[‘s, to 50% through the late 80’s and early 90’s, to 70%-80% in the mid to late 90’s.

Analyzing the mean monthly temperature in April, May, and June from 1950-1990, compared to the mean monthly temperature in April, May, and June of 1998 showed that the average temperature in Western Hudson Bay had been increasing at a rate of 0.2-0.3^oC per decade. The increase in temperature is thought to be the main reason the data collected of ice break up from 1979-1998 showed a trend towards earlier break up. If this were true the bears would have less time to hunt on the ice each winter because obviously there would be nothing to stand on. This would explain the poorer condition of male and female polar bears and natility.

Gloersen, P., and Campbell, W.J. 1991. Recent variations in Arctic and Antarctic sea-ice covers. Nature 352: 33-36

Johannessen, O.M., Miles, M.W., and Bjorgo, E. 1995. The Arctic’s shrinking sea ice. Nature 376: 126-127

Latour, P.B., 1981. Spatial Relationships and behaviors of polar bears concentrated on land during the free ice season of Hudson Bay. Canadian Journal of Zoology 59: 1763-1764.

McCormick, P.M., Thomason, L.W., and Trepte, C.R. 1995. Atmospheric effects of the Mt Pinatudo eruption. Nature 373: 399-404.

Ferguson, Steven H, et.al. 2000. Influence of sea ice Dynamics on Habitat selection by Polar Bears. Ecology. Vol 81. No. 3. 761-771.

Prinsenberg, S.J., 1980. Man-Made Changes in the Freahwater Input Rates of Hudson and James Bays. Canadian Journal of fish and aquatic Science. 37: 1101-1110.

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