Earlier this year, the U.S. Fish & Wildlife Service proposed listing the furry arctic denizens as threatened and subject to protected under the federal Endangered Species Act. More recently, the U.S. Geological Survey predicted that, by the middle of this century, the loss of Arctic sea ice caused by global warming will reduce the world's polar bear population by at least two-thirds.
If that news isn't grim enough, last month Norwegian scientist Janneche Utne Skaare told an audience at the Marine Environmental Research Institute that polar bears faced another threat to their survival. According to Skaare, persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs), pesticides and brominated flame retardants (BFRs) that reach the Arctic through the atmosphere are weakening the bears' immune systems and inhibiting their ability to reproduce.
POPs concentrate in the fat tissue of mammals and other animals. That means that animals higher up the food chain will tend to ingest higher levels of POPs in their diets.
For top predators like polar bears, that is a particular problem. The bears' favorite food is the blubber of the ringed seal — an excellent source of POPs. According to Skaare, the level of PCBs in the blood of polar bears has been found to be 100 times higher than that found in the breast milk of Norwegian women.
Skaare said it was wrong "to push your data" when asked if her findings meant that Arctic polar bears were endangered. That caution notwithstanding, in Svarlbard, where Skaare studied polar bears living in the archipelago lying midway between Norway and the North Pole, some evidence is clear.
Polar bears with high levels of POPs in their blood also have abnormally low levels of the primary immunoglobulin IgG. As a result, their weakened immune systems are less able to fight infections. That bodes ill for a bear population facing increased stresses from a radical change in their habitat.
The effects of high levels of POPs on the bears' reproduction are another cause for concern. According to Skaare, polar bears in Svarlbard seem to stop having cubs at a younger age than polar bears living in the Canadian Arctic, where POP levels seem to be lower than they are farther eastward. At the same time, bears on Svarlbard seem to have a faster reproductive cycle, bearing cubs two years apart rather than the normal three. With cubs staying close to their mothers for the first two and a half years of their lives so they can learn how to survive in harsh arctic conditions, the shorter time between births imposes additional stress on the bears.
There are other problems. POPs are known to affect the endocrine system and recently hermaphrodite polar bear cubs were discovered in Svarlbard where Skaare does her research.
According to Skaare, the combined effects of high levels of POPs and climate change present "a worst case scenario for polar bears."
High levels of POPs are not a new problem in the Arctic, Skaare said. The region has been threatened by POPs for at least four decades. At one time, PCBs were the major problem but since their production was banned in the late 1970s, the use of other POPs has increased. The result, Skaare said, is that while scientists have seen declining levels of PCBs in the blood and tissues of Arctic animals, there has been little or no net decline.
The news may be getting through to the world's political leaders. In 2005, the member nations to the Stockholm Convention on Persistent Organic Pollutants met in Uruguay to discuss expanded bans on the production and use of POPs.
Skaare offered some interesting insights into scientific methodology. Working with polar bears is extremely difficult. They are large — adult males weigh as much as 1,300 pounds — carnivorous and not docile. Skaare tranquilizes the bears with darts fired from on board a helicopter before taking blood and fat samples and a small tooth that reveals the bear's age, from these top-level predators.
Despite the difficulties presented by working with animals that, Skaare said, "you can't take into the laboratory," studying polar bears offers several benefits to a scientist concerned with the impact humans have on the planet.
"Nobody is interested in research on plankton," Skaare said. "My research is a wakeup to policy makers. It's also fun doing fieldwork."
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