Polar Bear Seal Diet Has Higher Contaminant Load: Impacts of Climate Change

Polar bears have to contend with a lot of threats. Now, they may have to deal with just one more. Over the past 30 years, polar bears have increasingly exchanged ring seal with harp seal and hooded seal in their diets. Scientists have now discovered that this change has exposed polar bears to far more contaminants, which may impact their health.

The polar bear is a species that's being drastically impacted by changing temperatures. Its habitat is shrinking and food sources are moving to adapt to the shifting climate. Because of this, polar bears have also had to adapt, though their populations are continuing to decline.

In order to better learn how this shifting climate might be impacting these bears, researchers decided to examine the East Greenlandic population of polar bears. While the Arctic sea ice in their habitat is expected to disappear very late, the ice sheet in the area is another matter. The decline of this ice sheet is occurring at a rate of almost one percent per year, which is one of the highest rates measured in the entire Arctic region.

The scientists examined the fatty acid profiles in the adipose tissue from a unique material of 310 polar bears that were hunted by East Greenland Inuits from the years 1984 to 2011. The composition of fat tissue of the polar bears reflected the profile of fatty acids in their diets.

So what did the researchers find? The bears fed primarily on three species of seal: the high Arctic ringed seal and the two sub-Arctic species of harp seal and hooded seal. Yet their diets have been changing over the years. Bears have begun eating more harp seals and hooded seals as the ringed seal disappeared.

"The problem is that the sub-Artic 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," said Rune Dietz, one of the researchers, in a news release. "Therefore, climate change undermines the improvements that you would otherwise have obtained owing to international regulations in the use of environmental use of persistent organic pollutants (POPs). We can see that the content of the POPs after year 2000 decreases slower in the polar bear than in the ringed seal."

While polar bears seem healthier with their new diet, the pollutants could drastically impact their health in the future. In addition, polar bears may lose access to the sub-Arctic seals since they depend on packed ice where they give birth to their pups. The findings reveal that polar bears may be facing more threats than we realized.

The findings are published in Global Change Biology and in two different papers in Environment International here and here.