Polar bears that hunt at sea are more polluted than those on land, study finds

POLAR bears that hunt at sea are more polluted than those which stay on land, a new study has found.

Climate change is accelerating the decline of Arctic sea-ice, which is forcing polar bears to alter their feeding and hunting habits.

And, according to the American Chemical Society, pelagic polar bears – which migrate annually to hunt at sea – have higher levels of pollutants in their bodies than their landlocked counterparts.

In recent decades, pelagic polars have shifted northward as southern ice has receded.

The bears now have further to migrate, whereas coastal bears – which stay on land to hunt – have tended to feed more on land-based prey or rely on their fatty reserves due to a lack of ice.

Previous studies have shown that pelagic bears have higher levels of pollutants, like persistent organic pollutants (POPS), in their bodies – but little is known about why that difference exists.

To solve this mystery, Dr Pierre Blevin at the Norwegian Polar Institute collected an array of data that paints a clearer picture of how climate change is affecting polar bears.

The researchers gathered data on the feeding habits, migration patterns, energy expenditure and geography to determine how the two polar bear types differed.

They also measured the pollutant levels in their prey.

The results indicated that several factors cause pelagic bears to accumulate more pollutants than those that stay on land.

Sea-based bears feed on a higher proportion of marine life, especially creatures higher up the food chain, meaning they are consuming more layers of polluted food compared to land hunters.

They also have higher energy requirements, which causes them to eat more – greater consumption of prey means ingesting more pollution.

Pelagic bears also feed on prey located closer to sources of pollution and transport pathways.

These factors show the unique pollution exposure mechanisms that polar bears face in this region.

Dr Blevin said: “In the Barents Sea, pelagic and coastal polar bears are facing various ecological challenges that may explain the difference in their pollutant levels.

“Our results indicate that pelagic polar bears from the Barents Sea are exposed to higher levels of pollutants than their coastal counterparts because they feed on higher proportion of marine and hightrophic level prey. They also have higher energy requirements and subsequently higher prey consumption, they forage in the marginal ice zones, and they feed on prey located closer to pollutant emission sources and transport pathways.

“Future studies should aim to predict how rapidly declining sea ice in the Barents Sea, which is likely to challenge polar bears energetically, will influence contaminant fate and exposure in Barents Sea polar bears.”

The paper is published in the latest issue of the American Chemical Society’s journal Environmental Science and Technology.