Fish, Bird Deaths Baffle, Alarm Scientists : Pollution Not Ruled Out in ‘Eco-Catastrophe’ at Nevada Refuge

An estimated 3 million fish and 1,500 migratory birds have died at the Stillwater National Wildlife Management Area near here in an environmental mystery that has baffled and alarmed biologists.

Dead fish--tui chub, eight- to 10-inch-long scavengers--line the 30-mile shoreline of the Carson Sink, a vast body of water that is a natural terminus for the Carson and Humboldt rivers in west-central Nevada.

“There were several fish along the shoreline that had small fish hanging out of their mouths. It looked like whatever killed them was fairly fast,” said Steven Thompson, a biologist with the U.S. Fish and Wildlife Service.

In the nearby bushes, dead ravens and pelicans hang grotesquely from the tangled branches.

While all the fish killed were tui chub, the devastation has stretched across a variety of bird species, including several varieties of ducks, cormorants, geese, egrets, blue herons, coots, ravens, California gulls and white pelicans.

Avian Cholera Found

Part of the mystery was solved Friday, when preliminary examination results on four of the birds showed that they died of natural causes--avian cholera. But officials and environmentalists said that disease does not explain all the deaths and the prospect that many may be attributed to pollution--perhaps to elevated levels of selenium and/or mercury--has not been ruled out.

“We’ve really been puzzled. It’s one of those things that you just don’t run into very often in your career. At this point we just don’t know. It’s baffling. We’re really stumped,” Thompson said.

“We’ve got a tremendous devastation of the wildlife habitat for unknown causes,” said Terry Young, a scientist with the San Francisco-based Environmental Defense Fund. She called the phenomenon an “eco-catastrophe.”

Earlier ‘Die-Offs’

There have been so-called wildlife “die-offs” at Stillwater before, and the Nevada refuge is one of a number of wildlife areas around the nation that some fear may be polluted. But the current episode is unprecedented in its scope. The deaths began shortly before last Christmas and cut across various species of birds with varying eating habits.

“We’ve never seen both (dead fish and birds) in the same area and never of this magnitude,” said Kenneth Merritt of the Nevada Department of Wildlife.

The Stillwater Wildlife Management Area is the home of the endangered bald eagle, the golden eagle and tens of thousands of migratory birds, some of which are officially placed on the “sensitive species” list. So far, no eagles have been found dead.

The first wave of hundreds of thousands of migrating birds returning from their wintering grounds are beginning to arrive here, and there are concerns that the deaths recorded so far may only be the beginning.

Carcasses of 24 dead birds were sent to the National Wildlife Health Center in Madison, Wis., for examination. The preliminary results of examinations on a raven and three ducks released Friday concluded the cause of death to be avian cholera.

But a second raven and a blue heron also examined showed no signs of avian cholera. Scientists were not able to immediately say what caused those deaths.

“It definitely appears there is more than one problem going on,” Kathryn Converse, a disease control specialist at the center, said in a telephone interview.

Officials at the refuge noted that all the dead birds do not have similar diets. For example, some feed on the chubs, but others do not.

Results of Tests Awaited

Examinations of the dead fish at a U.S. Fish and Wildlife Service laboratory in Columbia, Mo., have not been completed.

In addition, the U.S. Geological Survey in Denver is testing samples of highly saline water taken from the refuge for the presence of any heavy metals, arsenic, selenium, hazardous compounds or low oxygen content caused by algae. Thompson said the salinity of the water is so high that it is about half as salty as the ocean.

Thompson added that preliminary test results prompted an immediate effort to dispose of the 1,500 bird carcasses to prevent the further spread of avian cholera.

Developments at Stillwater are also of major interest to wildlife authorities and environmentalists because of possible parallels to the Kesterson National Wildlife Refuge near Los Banos, Calif.

Bird deaths and birth deformities at Kesterson have been traced to high levels of selenium that have drained into the refuge from agricultural waste water. Selenium is a naturally occurring element that is necessary to life in small amounts but can be poisonous in large doses.

The Kesterson situation, considered the worst environmental degradation of a wildlife refuge in the nation, has focused national attention on the state of wildlife refuges.

High Levels of Selenium

High levels of selenium have been recorded at or near 20 other national refuges, including Stillwater.

Like Kesterson, Stillwater is a sink. The rivers in northern Nevada have no outlet to the sea and instead flow into a vast marsh area and the Carson Sink, which is 15 miles wide and 20 miles long. This has led to fears that, like Kesterson, selenium may have built up to dangerous levels in the sink.

The Stillwater Wildlife Management Area has long been plagued by elevated levels of selenium and mercury washed down from the historic gold and silver mines of the Comstock lode. Officials estimate that as many as 7,500 tons of mercury alone washed through the river system.

Three years ago the Carson and Humboldt rivers reached flood stage, and the Carson and Humboldt sinks filled to capacity. They have since receded about 40%.

Some speculate that the floodwater may have freed mercury and other elements that had been embedded in the mud flats, allowing it to migrate into the water and the food chain.

But, for the moment, biologists here said there is more that they do not know and none said they are ready to offer a full explanation for the disaster.