New research indicates that polar bears in the western Arctic are finding it increasingly difficult to find food during the critical spring season.The study by Seth Cherry and Andrew Derocher of the University of Alberta reveals that the number of undernourished bars has tripled in the past twenty years.
The Alberta scientists and their colleagues monitored the health of polar bears in the Beaufort Sea region during the spring of 1985/86 and then again in 2005/06 when sea ice cover was at or near record lows.
The scientists measured the ratio of urea to creatinine - byproducts of metabolism - to determine how much the bears are eating. A low ratio means that nitrogenous waste material is being recycled in the body, indicating the bear is fasting.
In springtime mature males spend most of their energy looking for mates, so it is not unusual to see some of these animals going without food for considerable lengths of time. Nonetheless, the blood samples taken from bears in 2005/06 showed a marked increase in the number of bears that were fasting. Additionally, the fasting was for longer periods of time and it made no difference how old the bears were or if they were male or female. According to the research, nearly a third of the bears monitored were going without food longer than they normally would.
Polar bears use sea ice as a platform for hunting seals. Other than the normal fasting of males looking for females, springtime is typically a time of feasting for polar bears as they fill up before the summer sea ice retreat. The scientists believe that the increase in undernourished bears is explained by warmer seas and earlier spring melts.
It is clear that the changes in the sea ice are affecting the hunting opportunities available to the bears," says Derocher.
Not only is the early melt affecting the bears ability to hunt, it could also have significant impact on the prey for which they hunt. The diminishing sea ice impedes the seals' ability to nurse and build dens for their pups, causing their numbers to drop.
Anecdotally, there are increased sightings of bears swimming in open water and eating food not customary to their diets, such as fish. Other research has shown that melting ice is driving pregnant mothers onto land to build their birthing dens.
If the ice continues to contract, which seems inevitable, polar bears will become even more nutritionally disadvantaged. The study proves polar bears are in serious trouble," says Rick Steiner, a marine conservationist at the University of Alaska in Anchorage.