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SANTA CRUZ, California -- As long-lived predators at the top of the marine food chain, albatrosses accumulate toxic contaminants such as PCBs, DDT, and mercury in their bodies. A new study has found dramatic differences in contaminant levels between two closely related albatross species that forage in different areas of the North Pacific. Researchers also found that levels of PCBs and DDT have increased in both species over the past ten years.
The differences in contaminant levels between black-footed and Laysan albatrosses indicate regional differences in the contamination of North Pacific waters, said Myra Finkelstein, a postdoctoral researcher at the University of California, Santa Cruz, who led the study.
"The black-footed albatrosses forage mostly in the California Current, whereas the Laysan albatrosses forage at higher latitudes near Alaska. So it appears that the California Current system has significantly higher concentrations of these contaminants," Finkelstein said.
The researchers published their findings in the April issue of the journal Ecological Applications.
Mercury and organochlorine compounds such as PCBs (polychlorinated biphenyls), DDT, and related compounds persist in the environment for a long time and build up in the tissues of animals high on the food chain. Analysis of blood samples showed that concentrations of these compounds in black-footed albatrosses were 370 to 460 percent higher than in Laysan albatrosses.
The two species breed at the same sites in the Hawaiian Islands. But when they leave their breeding colonies on foraging trips, the black-footed albatrosses head northeast toward the West Coast of North America, while Laysan albatrosses head northwest toward the northern and western regions of the North Pacific.
Black-footed and Laysan albatrosses both consume a mixed diet of squid, fish, and fish eggs. Finkelstein analyzed nitrogen isotope ratios in the two species--an indicator of an animal's "trophic level," or how high it is on the food chain--and found no significant difference.
"Biomagnification means that you get higher concentrations of these compounds as you go up the food chain, but these species appear to be feeding at the same trophic level. We saw huge differences in contaminant levels, which we attribute, at least in part, to the differences in foraging patterns between the two species," Finkelstein said.
The high contaminant load in black-footed albatrosses foraging in the California Current probably reflects the long history of industrial and agricultural discharges along the West Coast, Finkelstein said. But she added that the distribution and transport of contaminants in the North Pacific involves processes that are still not fully understood.
Concentrations of DDE (the main breakdown product of DDT) and PCBs in both black-footed and Laysan albatrosses were 130 to 360 percent higher in the samples Finkelstein collected in 2000 and 2001 than in samples collected by previous researchers in 1991 and 1992. The increases were much greater in black-footed albatrosses than in Laysan albatrosses, Finkelstein noted. DDE concentrations, for example, increased 360 percent in black-footed and 170 percent in Laysan albatrosses.
Many countries do not regulate the manufacture and use of PCBs and DDT as strictly as the United States does now, and these compounds continue to be released into the marine environment.
"The increases we saw compared with ten years ago probably reflect the ongoing use of these chemicals in countries that border the Pacific," Finkelstein said.
The biggest current threat to albatross populations in the North Pacific is the longline fishing industry, which kills significant numbers of both black-footed and Laysan albatrosses. But the contaminants measured in this study may also take a toll. Comparable levels of these contaminants in other species, such as herring gulls and Caspian terns in the Great Lakes region, have been associated with a variety of adverse effects, including reproductive deformities, endocrine disruption, and immune system dysfunction.
"It is very difficult to show a cause-and-effect link in a wild population, but there is evidence of health impacts in other species at these contaminant levels," Finkelstein said.
Humans are exposed to the same contaminants when they eat seafood, she added.
"It is important to realize that these contaminants have long-term effects, and we are only beginning to understand many of the subtle effects they can have, such as endocrine disruption and effects on the immune system," she said. "A lot of people think this issue has been taken care of, but it is still very much a problem."