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Fail to Hatch

It's no wonder the California clapper rail is endangered. Foxes and rats are scarfing the species, cities are engulfing its habitat and pollution is contaminating its food. Just how much this contamination is contributing to the rail's demise is the domain of a recent study by U.S. Fish & Wildlife's Steve Schwarzbach.

"To recover the rail in the long term, we're going to have to build some wetlands," says Schwarzbach. "We need to know what level of risk we can expect from contamination in any sediments we use; an idea of how clean is clean."

In a 1991-1992 study, Schwarzbach and the S.F. Bay Wildlife Refuge's Joy Albertson examined eggs from 71 rail nests in five S.F. Bay marshes. Schwarzbach measured mercury and other contaminant levels in the eggs and recorded abnormal development, looking for telltale signs of contaminant impacts. To support the nesting study, he measured contaminants in sediments and rail food - purple shore crabs, ribbed horse mussels and mudsnails - collected near nest sites. This integrated study gave him just what he was after.

"We've now got a bioaccumulation factor from sediment to eggs for mercury," he says. Scientists can now take a mercury concentration level in sediments and multiply it by Schwarzbach's factor of 2.427 to predict concentrations in rail eggs.

Schwarzbach found a mean mercury level in sediments of 0.366 parts per million (ppm), a level distinctly higher than the 0.237 ppm at his North Bay reference site. Snails turned out to be the most contaminated prey items, posing a significant hazard. Mercury in the "fail-to-hatch" eggs ranged from 0.19-2.7 ppm. Other lab studies indicate that the lowest observed adverse effect level in avian eggs is 0.5 ppm; at 5.0 ppm embryo mortality soars.

Schwarzbach also measured silver, selenium and DDE (a DDT derivative) and found that concentrations were not elevated to problem levels. He says PCBs may require further investigation. "The one chemical clearly elevated into the toxic risk threshold was mercury," he says.

All marshes in the study had abnormally high numbers of non-viable eggs (13.7 - 22.9%). Normal hatchability in rails, even with predation and losses to tides, should exceed 90% according to other studies. Schwarzbach's study is due for publication this summer.

Contact: Steve Schwarzbach (916)978-5616

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