Scientific Symposium Presentation Abstracts
September 19
Dr. Andrew E. Derocher: Polar Bears in a Warming Arctic
Surviving in the frigid Arctic, through months of winter darkness, and roaming over huge areas; few species are as enigmatic as the polar bear. The species is only a few hundred thousand years old and evolved in a rapid burst of evolution from a grizzly/brown bear ancestor. With numerous specialized adaptations, they rapidly exploited a vacant niche on the sea ice of the Arctic as an obligate predator of seals. Sea ice is their primary habitat and is used as the platform for traveling, hunting, mating and in some areas, for denning. The key to the success of polar bears lies in exploiting the fat of other marine mammals and turning it into a portable food store for periods when food is unavailable. While superbly adapted to the highly variable conditions in the Arctic, polar bears live close to the limit of what is biologically possible. Pregnant females can successfully fast for over 8 months while over-wintering in dens and rearing cubs, which are born weighing about 600 grams (1.5 lbs). Their success at rearing offspring, however, is tied to how much fat they are able to store and this in turn is linked to the dynamics of their sea ice habitat. Change the sea ice and their ability to hunt is affected. Take away or alter the sea ice too much and the bears are pushed beyond their limits and populations decline through reduced recruitment.
Polar bears live in 19 relatively discrete populations around the circumpolar north and the effects of climate warming are becoming evident throughout their range. The effects are most evident in the Western Hudson Bay population in Canada, which has declined by over 20% in the last decade and in the Southern Beaufort Sea population off Alaska and northwestern Canada, which has dropped by over 10% in two decades. Changes in sea ice conditions are implicated in both areas. While these rates of decline may seem low, for long-lived mammals with low reproductive potential, the rates are a serious concern for the persistence of the populations. Most other populations lack sufficient monitoring to determine their trends, but symptoms of climate change are chronic and increasing in regularity. Other indicators include declining body condition, reduced reproductive rates, lower survival rates, drowning, cannibalism, increased number of problem bears, and changes in distribution.
If climate warming continues unchecked, the persistence of many polar bear populations is doubtful. Recently, the IUCN/SSC Polar Bear Specialist Group, representing the expertise of the five nations with polar bear populations, raised the level of conservation concern for the species. Polar bears are now listed as “Vulnerable,” which means they are considered to be facing a high risk of extinction in the wild. The time frame of concern varies for each population, but an overall decline exceeding 30% is possible within the next 35 to 50 years: the world could lose over 8,000 polar bears within 3 generations of bears. Future challenges for conserving polar bears and their Arctic habitat will be greater than at any time in the past because of the rapid rate at which environmental change is occurring.
