Bird Deaths at Salton Sea Blamed on Toxic Algae

Thousands of water birds that died mysteriously at the Salton Sea National Wildlife Refuge apparently were poisoned by a toxic form of algae that blooms in the huge salty lake, according to new findings by the U.S. Fish and Wildlife Service.

Clark Bloom, manager of the federal refuge, said the discovery--although preliminary--is a great relief because the bird deaths have perplexed and worried wildlife biologists since they began three years ago.

“It was extremely frustrating to go through this,” Bloom said. “The only thing we did know is that we were picking up a lot of bodies.”

About 15,000 eared grebes wintering at the Salton Sea died in February and March of 1992 and another 20,000 died during the same period in 1994. No mass die-offs occurred this year or in 1993, adding to the mystery.

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Until the newly completed tests were conducted, federal biologists had been stumped after ruling out common infectious diseases and chemical pollutants. Tests on the carcasses of grebes detected high concentrations of a poison, called microcystin, in their livers. Microcystin, produced by blue-green algae, has no known antidote.

In some birds, the toxin was “high enough to account for acute lethal liver toxicosis,” according to a report by Wayne Carmichael, an aquatic biologist at Wright State University in Ohio. In others, the amount was lower but still high enough to possibly contribute to their deaths. The grebes probably ingested it by drinking the water.

Located in farm-rich Imperial County near the U.S.-Mexico border, the Salton Sea is a major wintering ground for migratory birds from throughout the Pacific Flyway, including eared grebes, which are foot-long water birds with red eyes and golden ear tufts.

Preventing mass deaths could be difficult because the algae is probably nourished by fertilizers and other nitrogen-based pollutants, called nutrients, that flow into the Salton Sea via runoff from farms and tributaries of the Colorado River. Sewage from Mexicali, Mexico, also could be contributing nutrients that cause algae growth.

“Typically, that’s what causes very large algae blooms--that there are unlimited amounts of nutrients,” said Jewel Bennett, a contaminants specialist with the Fish and Wildlife Service in Carlsbad.

The wildlife agency began investigating whether toxic algae was involved after a series of articles in The Times last year reported widespread deaths of fish and other aquatic life along the East Coast because of toxic organisms in algal blooms fed by fertilizer and sewage.

Some aquatic biologists say the toxic algae problem is becoming a global epidemic because of nutrient-rich runoff. Most blue-green algae blooms are nontoxic, but some toxic blooms have been reported worldwide, including ones linked to human illnesses in Canada, India and Australia.

Although the link is not conclusive, Bloom said, there is “pretty good preliminary evidence that blue-green algae was involved.”

“So far, everyone is cautiously optimistic that this may really lead to a fuller explanation of what happened with the die-offs,” Bennett said. “At least all the birds had some toxin in them. The thing is, we don’t really know what is a lethal amount in a grebe.”

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A more comprehensive study will begin next month to try to confirm the link with toxic algae and find the sources of nutrients that nourish it.

The toxin apparently kills by destroying a B vitamin, thiamine, and targeting the liver, resulting in hemorrhaging or liver failure and death within a few hours to days, according to research by North Carolina State University aquatic ecologist JoAnn Burkholder.

A tiny amount--measured in parts per billion--seems fatal to the grebes. No other species died. Bloom said at the time of the deaths that the grebes were preparing for their long migration back north, so their immunity could have been impaired.

“Maybe they are more sensitive or maybe they’re having a different kind of exposure,” Bennett said.