August 4, 1997
This sea otter's brethren in the Aleutian Islands carry high levels of PCB
By Mari N. Jensen
Remote islands of surreal beauty, the foggy, windswept Aleutians are thousands of miles from heavily populated areas. Even so, the islands harbor a nasty reminder of human activity: Sea otters and bald eagle eggs from the western Aleutians carry potentially harmful levels of DDT and other contaminants.
A team led by UCSC scientists found that sea otters from the western Aleutians contained almost twice as much of the industrial compound PCB as otters from the central California coast, an area known to have agricultural and industrial contamination. The otters also carried almost 40 times more PCBs than otters from a relatively uncontaminated site in southeast Alaska.
Such high PCB levels may have an insidious effect on the otters' health. Similarly high levels can cause reproductive failure in mink, a closely related species.
Bald eagle eggs contained elevated levels of both DDT and PCB. DDT, known to thin the eggshells of birds of prey elsewhere, may harm these raptors as well: Eagles on the island with the highest levels of DDT are reproducing at half the rate of those on other islands.
Although the researchers can't pinpoint the sources of the pollutants, their distribution patterns yield some clues. The PCBs may come from former military activity on some of the islands; the DDT could be windborne or waterborne contamination from agricultural use in Asia.
"We expected the Aleutians would be very clean because it's a remote oceanic environment--that's why we picked it," said James Estes, a wildlife biologist with the U.S. Geological Survey and UCSC. "We found these high levels in the Aleutian Islands, higher even than in California, so that was a big surprise. The levels of compounds in these animals are alarmingly high."
Estes and several colleagues published their work in the current issue of Marine Pollution Bulletin. Coauthors are researchers Corinne Bacon and Walter Jarman of UCSC's Institute of Marine Sciences; Ross Norstrom of the Canadian Wildlife Service; and Robert Anthony and Keith Miles of the U.S. Geological Survey at Oregon State University and UC Davis, respectively.
Sea otter populations are still recovering from intensive hunting in the 1700s and 1800s. Most otter populations in Alaska and the Aleutians are now growing at almost 20 percent per year, a healthy rate. In contrast, the California population is increasing at just 5 percent per year and is still listed under the Endangered Species Act as threatened.
To investigate whether contaminants such as DDT and PCB are impeding the recovery of sea otter populations off California's Central Coast, the researchers compared contaminant levels in the livers of California sea otters to otters from sites believed to be clean. To test for pollutants, the team collected carcasses from beaches in central California and on the Aleutian island of Adak in 1991 and 1992. Alaskan Natives provided otter carcasses from southeast Alaska.
Surprisingly, California's otters did not carry the highest amount of PCBs. That dubious honor went to the otters from Adak. Their livers harbored 309 parts per billion total PCBs, while California otters had 185 parts per billion, and those from southeast Alaska had only eight.
Because they found no dead otters on the other Aleutian Islands, the scientists also collected bald eagle eggs that had failed to hatch. That analysis confirmed the PCB contamination in the western Aleutians, particularly on the islands of Adak, Amchitka, and Kiska. DDT also contaminated the eagle eggs, and it exhibited a striking trend: The further west the island, the more DDT.
These patterns provide clues to the pollutants' origins. The PCBs may come from military operations: Eggs from the three islands with former military activity had four times more PCBs than eggs from Tanaga, the only island that has not been a military site. Since eggs from the more westerly islands have higher DDT levels, that subtance may come from Asia via wind and water currents.
"Anytime you see DDT, it's a recent application, within the last few months or years," Jarman said. "One theory is that if they use a ton of it in China, we'll see it in the Aleutians." DDT also may come to the Aleutians via migratory animals, especially birds, Estes noted.
Other studies also hint at trouble for the region's marine birds and mammals. Said Estes: "That whole North Pacific ecosystem is a worry because lots of things are declining--the Stellar sea lion, for instance. It raised the issue in our minds that maybe contaminants were playing some role."
After the team completed its study, Estes discovered that otter populations on Adak are not faring as well as previously. With funding from the Department of the Navy, the team is starting a more detailed investigation of contamination levels in otters from the western Aleutians to southeast Alaska. Jarman said, "I expect there'll be hot spots and clean spots."
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