September 20, 2013
Climate Woes Continue: Changes In Polar Bear Diet Result In Higher Toxin Exposure
Brett Smith for redOrbit.com - Your Universe Online
Warmer than average Arctic temperatures in recent years have been stirring up all kinds of ecological changes and a new study in the journal Global Change Biology indicates that polar bears could be getting exposed to higher levels of toxins as a result.
The study looked at an East Greenlandic population of polar bears, which is expected to enjoy the Arctic sea ice far longer than other regions. However, the loss of ice sheet cover in these waters occurs at a rate of nearly 1 percent per year, one of the highest rates across the entire Arctic.
To see how the changes have affected the bears, a team of international scientists examined the fatty acid composition of adipose tissue collected from 310 polar bears hunted by East Greenland Inuits from 1984 to 2011. The makeup of fatty acids in the adipose tissue samples reflected the profile of fatty acids in the bears’ prey.
The researchers saw that the bears mostly fed on three species of seals: the ringed seal, which inhabits the Arctic, and the two sub-Arctic species – the harp seal and hooded seal. The study’s results also showed that the polar bears have significantly changed their diet over the nearly 30 years covered by the samples.
Over the study period, the ringed seal’s significance for the polar bears diet dropped by 42 percent as the bears’ intake of the sub-Arctic seals increased. The team also found that polar bears are generally in better shape now.
At first glance, the polar bears would seem to be better off these days. However, a deeper analysis revealed several problems.
"The problem is that the sub-Arctic seals that the polar bear has switched to, have a higher content of contaminants because they live closer to the industrialized world and are higher up in the food chain,” explained study author Rune Dietz, a biology professor at Aarhus University. He added that climate change undermines the improvements that they would otherwise have obtained owing to international regulations in the environmental use of persistent organic pollutants (POPs). They determined that the content of the POPs after year 2000 decreased more slowly in the polar bear than in the ringed seal.
Although warmer temperature may mean these sub-Arctic seals are traveling farther north, the researchers said the long-term prospects for accessing these seals could decline as they depend on packed ice to birth their cubs and receive vital vitamin D-forming sunlight.
While polar bears off the coast of Greenland may be enjoying a greater, albeit more polluted, variety of food, their counterparts in northern Canada and off the coast of Alaska appear to be less well off.
Recent research has found that these bears have been exhibiting lowered reproductive abilities, lowered average body weight and decreases in overall population.
Based on a study published earlier this month by Global Change Biology, a team of American and Canadian researchers said an array of environmental differences are affecting the health of polar bears in East Greenland.