Bear Trouble- page 3 | Science | Smithsonian
Having stopped a mother bear with a tranquilizer dart shot from the helicopter, Derocher (with Andersen, left, and Instanes, on Spitsbergen Island) tethers the cubs and takes tissue samples to gauge the mother's exposure to industrial chemicals like PCBs. (Marla Cone)

Bear Trouble

Only hundreds of miles from the North Pole, industrial chemicals threaten the Arctic's greatest predator

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Derocher, whose towering height, jet-black hair and full beard give him the aura of a big bear himself, is guided by an internal compass that steers him north, far north, whenever he craves serenity. He was raised along the lush banks of British Columbia’s FraserRiver, where he collected bird eggs and garter snakes and fished for salmon fry. He studied forest biology at the University of British Columbia and earned his doctorate in zoology at the University of Alberta. When he ventured into the Canadian Arctic for the first time as a young researcher, it struck him as barren. Then, his mentor, Ian Stirling, a polar bear expert at the Canadian Wildlife Service, dropped a hydrophone into the sea. Derocher listened to whales singing, seals grunting, ice grinding. When he heard that undersea symphony and also saw bloodstains on the ice left by feasting polar bears, he realized the place was far from being a sterile wasteland and was hooked.

The Arctic “is the end of civilization,” he says. “Far off on the ice, there is an immense sense of peace and remoteness that you can’t find in many places in the world anymore.”
Since the early 1980s, he had dreamed of studying polar bears in their purest form, of finding a pristine population, and when he first set foot in Svalbard, in 1996, he thought he had found polar paradise. The animals had not been hunted or trapped since 1973, so their population should have been booming. But something was amiss. “Things just don’t appear right,” he told colleagues within a year of arriving.

It was as if the bears were still being hunted. Where were the older bears? Why were there so few of them? Why wasn’t the population growing more quickly? A lot of cubs, he found, didn’t make it. Were they more prone to die than cubs in North America? And then Derocher came across strange, pseudo-hermaphroditic female bears with both a vagina and a small penis-like appendage. “Within the first year, it became pretty darned clear that I wasn’t working with an unperturbed population,” he says.

He began to think the reason might be chemical contaminants. Other scientists had been gathering evidence that although the world of the polar bear is as white as the driven snow, it’s not pure after all. Derocher has found the highest PCB levels in Svalbard’s male bears, with as much as 80 parts of the chemical per million parts of body tissue. (Researchers have not established a precise toxic threshold for PCBs in polar bears.) On average, male bears in Svalbard carry 12 times more of the chemical contaminant in their bodies than do male bears in Alaska. In living wild mammals, higher PCB levels have been found only in Pacific Northwest orcas, Baltic seals and St. Lawrence River beluga whales. Svalbard’s bears carry “alarmingly high” concentrations of PCBs, says Janneche Utne Skaare, of Norway’s National Veterinary Institute, who conducts polar bear contaminants research.

The snow is clean. The air is clean. Even the water is clean. So where is this toxic trash coming from? Though PCBs were banned in the late 1970s in most of the world, the compounds, once widely used as insulating and cooling fluids in electrical equipment, are remarkably persistent. In a way, climate and geology conspire to transport PCBs to the Arctic, which in the view of some scientists, is becoming a sort of giant pollution sink. Prevailing winds sweep air pollution from eastern North America, Europe and Russia northward. Svalbard in particular is something of a crossroads, buffeted by three seas and the Arctic Ocean. In a phenomenon that scientists call the grasshopper effect, PCBs from, say, a discarded transformer on the Eastern Seaboard can repeatedly evaporate in warm weather, ride the wind and fall to the ground until they’ve hopscotched to the Arctic, where they land on snowfields and in frigid seas and are trapped. The chemicals work their way up the marine food chain, step-by-step. From water to plankton to crustaceans to cod to ringed seals to polar bears—with each link, PCBs can become 10 to 20 times more concentrated. Predators at the top of the chain thus take in the highest dosages. A polar bear can carry a million times the concentration of PCBs detected in seawater. And a mother that harbors contaminants in her fatty tissue passes them on to her suckling newborn. When newborn cubs feast on their mother’s milk, they feast upon her past.

Norwegian and Canadian scientists have recently linked a variety of effects in the bears to PCBs, including alterations in immune cells, antibodies, retinol, thyroid hormones, testosterone and progesterone. The scientists don’t know what these biological changes mean to the health of individual bears or the whole population. But they have recently amassed disturbing signs of trouble.

Scientists testing bears in Canada have found that concentrations of PCBs were three times higher in denning mothers that wound up losing their cubs than in mothers whose cubs survived. Skaare speculates that pollutants are taking a toll on Svalbard’s bears, too; they seem to den more often than other bears, about every two years instead of every three, which suggests that an unusual number of cubs are not surviving.

Evidence is also mounting that PCBs are suppressing the bears’ immunity to disease. The ability to rapidly produce large volumes of antibodies against viruses and infections is critical for survival. But polar bears with high amounts of PCBs can’t muster up many antibodies, and levels of the immune cells called lymphocytes are suppressed, according to Derocher and other researchers. Bears in Canada, which carry far less PCBs, produce more antibodies than Svalbard bears. Hinting at the capacity of PCBs to weaken the immune system with disastrous effects, a distemper virus wiped out some 20,000 PCB-laden seals in Europe in 1988.

Derocher has also documented altered levels of testosterone in male bears and progesterone in female bears, and he suspects that PCBs may be the reason for the disrupted reproductive hormones. He’s trying to determine whether PCB-carrying bears are also less fertile than other bears and whether the contaminants account for Svalbard’s pseudohermaphroditic bears. (Out of every 100 female bears captured, 3 or 4 also have the genital abnormality.) PCBs also seem to deplete the bears’ reserves of retinol, or vitamin A, which is critical for regulating growth.

Some scientists say that the polar bear population is lower than expected, and they wonder if PCBs are to blame for what they describe as a missing generation. Contaminant levels in Svalbard bears peaked in the late 1970s through the early ’90s. And studies showed that the bears had seven times more of some PCBs in their bodies in the early 1990s than in 1967. At the same time, researchers have found a dearth of bears born in Svalbard when pollution levels peaked. In one study, only 13 percent of Svalbard bears with cubs were over 15 years old, compared with 40 percent in Canada. Geir Wing Gabrielsen, director of ecotoxicology research at the Norwegian Polar Institute, says it is obvious that Svalbard bears have been weakened. “Everything indicates that the polar bear is being affected by these contaminants,” he said. “There are so many indications that there are population effects.”

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