Global Warming Driving Polar Bears to Eat Toxic Diet

Polar Bear

Researchers say that, thanks to global warming, polar bears in eastern Greenland are being forced to switch up their diet, eating more harp seals and hooded seals and fewer ringed seals.  Unfortunately this also means that they are consuming a more toxic diet.

The team that made this discovery was composed of scientists from the Greenland Institute of Natural Resources, Aarhus University in Denmark and several institutions from Canada, including Dalhousie University, Great Lakes Institute for Environmental Research, University of Windsor, Carleton University and the National Water Research Institute.

In order to see just how their dietary changes were affecting the bears, the team analyzed the fatty acid profiles in their adipose, or fat, tissue.  They took their samples from 310 polar bears that had been hunted by the indigenous population of the Scoresbyund area during the period between 1984 and 2011.  They wanted to analyze the fatty acids in their tissues because it would very closely reflect the fatty acids found in their diet.  Different species of seals have a different blends of fatty acids in their tissues so these differences could be used to estimate how much of each type of seal the bears had eaten.

Because they had three decades of data to study, they were able to see that the polar bears’ diet had drastically changed during this time period.  They had turned away from their preferred ringed seals and had increased their consumption of harp seals and hooded seals.

Unfortunately for the bears, these animals’ tissues are also more contaminated with pollutants; and, a high level of contamination was also found in the bears’ tissues.

The problem, according to Rune Dietz of Aarhus University, is that these seals live closer to industrialized areas and thus are exposed to more toxins in their own food supply.  And, when the polar bears eat their flesh, they too are exposed to more toxins.

Global warming has forced this dietary change upon the polar bears, Dietz says.  Ringed seals, which used to the bears’ primary food source, like to live on ice floes.  However, as the Arctic ice has shrunk, the bears have begun to swim further  and further out to sea in search of other food sources.  So, ringed seals, which once made up about 90 percent of their diet, now only account for about 34 percent of their food intake.

Among the chemicals which were found in the bears’ fatty tissues were DDT (a pesticide which was banned in the United States in 1972), polychlorinated biphenyls (PCBs), and other materials, known as persistent organic pollutants (POPs).  POPs are substances which do not break down easily in the environment so they tend to linger for many years.

According to Dietz, they should have seen declining levels of toxic substances in the polar bears’ tissues due to stricter environmental regulations.  Unfortunately, global warming has counteracted these efforts by driving the polar bears to change their diet.

Written by:  Nancy Schimelpfening

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