| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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habitats Salton Sea SicknessI am following an irrigation canal under a 102-degree, mid-day sun down a dirt path through brilliant green alfalfa fields, looking for the dirtiest river in America, which I hope to follow to California's largest lake and one of the best places to watch birds in the world. I have been advised by Ken Sturm, the biologist at the Salton Sea National Wildlife Refuge, of which this land is a part, not to take this walk. He warned about "health concerns" of walking to the mouth of the New River. The river flows north across the Mexican border from Mexicali carrying industrial waste, raw sewage, slaughterhouse remains, and the pesticides and selenium that taint agricultural runoff. But he also said that the birding at the river's mouth would be "mind blowing." Before I reach the New River it is hard to believe there are birds nearby. All I can see is endless fields of alfalfa. Although it is late October, it is surprisingly hot and I am soaked with sweat and am beginning to wonder if I am walking in the right direction. But when the path climbs a graded levee my nose tells me that I have come to the right wrong place. The New River, its dark brown water gliding silently and heavily by, looks viscous and the occasional bottle or shaving cream can seems to ride high, as if in a river of lava. To my right the alfalfa fields give way to a salt-encrusted marsh that lines this part of the Salton Sea. A great blue heron flies low over my head and lets out a call that must announce my presence for it signals the beginning of avian pandemonium. Suddenly birds are everywhere: grebes, cormorants, all kinds of egrets and herons, ducks, American kestrels, rails, plovers, gulls, so many different kinds that I cannot keep track. What has brought me here to the Salton Sea is an outbreak of avian botulism. It hit the sea's bird population, especially pelicans, with devastating force last summer, and it brought to an abrupt end the denial and complacency which have characterized both official and public attitudes about this unearthly life line for millions of birds. In mid-August biologists noticed an unusual number of bird deaths concentrated mostly in the south part of the sea, where the wildlife refuge is and where the New River makes its constant toxic deposits. By September a small interagency army of wildlife professionals were picking as many as 500 dead birds a day off the sea's surface and beaches. By far the hardest hit species were the pelicans. When the summer was over 8,519 whites, and more than 1,125 endangered brown pelicans, were dead. This summer's Salton Sea debacle constituted the largest known pelican die-off anywhere, ever. Daniel Anderson, a pelican specialist at the University of California at Davis, says that brown pelicans nested here for the first time this summer and that he suspects whites would soon have followed. That's "most unlikely" now, he says. In fact, he adds, not only did the summer's epidemic probably dash hopes raised earlier this year of removing the brown pelican from the endangered species list, but it raised the possibility of putting western whites onto it. Though botulism C (also known as avian botulism) is a naturally occurring organism and has, as far as anyone knows, always existed in these parts, its infection of the pelicans was a surprise to the refuge managers and other biologists. Pelicans don't usually get avian botulism because they only eat living fish. And until now, only dead fish have carried dangerous amounts of the toxin, which is produced by bacteria that thrive in the kind of oxygenless, protein-rich environment corpses provide. Why then were more pelicans dying of botulism than any other birds, including those, such as turkey vultures, who don't mind pecking at corpses for a living? Answering this question required toxicological and pathological studies of the tilapia, by far the most abundant fish in the Salton Sea. Scientists at the U.S. Geological Survey's National Wildlife Health Center in Madison, Wisconsin discovered that some living fish contained botulism toxin in sufficient concentrations to kill the pelicans, which are relatively sensitive to the toxin. Frank Shipley, Director of the Northwest Biological Science Center in Seattle, says that the sick tilapia were massively infected with a pathogenic bacteria: Vibrio alginolyticus. Shipley's lab, working with disease specialists in Madison, discovered that infections in sick tilapia were causing lesions, swelling of the body cavity, and major, fatal changes in the internal organs. The scientists hypothesized that the massive changes in the fish gut could have triggered germination of botulism spores, followed by secretion of toxin inside the living fish. The tilapia, while dying of vibrio infections, would also be harboring fatal doses of botulism when they were eaten alive by the pelicans. No one has seen this infection and poisoning mechanism before, according to Shipley. Where did the Vibrio pathogen come from and why did it hit the fish when it did? "Nobody knows," says Sturm. "There are literally hundreds of freshwater inputs into the Salton Sea. We don't even know if the fish are getting the pathogen at a single point or from numerous places around the sea." It is also possible that the pathogen has been there all the time, says Shipley, and that the combination of stresses weighing on the tilapia (overcrowding, increasing salinity, increasing selenium, and pollutants) finally weakened their resistance. "Right now," he says, "there is simply not enough background science on the ecosystem to tell us even enough to make smart guesses." Startlingly little is known about California's biggest lake, despite the fact that it has become a crucial link for millions of birds that migrate along the Pacific Flyway and host to at least four endangered bird species: the peregrine falcon, the Yuma clapper rail, the bald eagle, and the brown pelican. "It's much more important for wildlife than Mono Lake," says limnologist Stuart Hurlbert of San Diego State University. "But it doesn't get the same kind of attention: first because it's got such a bad reputation from news stories about the New River and second because it's an artificial body of water. It doesn't have the same allure." When I asked Hurlbert if the New River's reputation was deserved he said that nobody really knows. "No one wants to get close enough to take samples," he says. And when they do take samples they have to get dressed in hot, astronaut-like protective suits. In temperatures that commonly reach 115 ¼F, that makes for less than comfortable fieldwork.
The Salton Sea was created by accident 90 years ago when water diversion dikes inadequately built along the Colorado River collapsed during a flood. For about a year and a half the Colorado, flooding the channel now occupied by the New River, emptied into the ancient Salton Basin before it was brought under control and redirected into Imperial Valley irrigation or down to the Gulf of Mexico. With these high temperatures, and fewer than two inches of rain a year, that water evaporated a long time ago. But the sea is now the official catchment of the Imperial Valley's agricultural runoff. It is this runoff, along with the New River, that maintains the sea and keeps it growing. Because the Salton Sea has no outlets and is sometimes fed faster than its waters can evaporate, it grows in fits and starts, alternately swallowing and spitting back beachfront hamlets. "The Sea is a sump," says Sturm. "Anything you put in stays there and collects in higher and higher concentrations: salt, pesticides, selenium, whatever." When it first formed, the Salton Sea was fresh water and contained trout and other Colorado River species. Today it is 25 percent saltier than the Pacific Ocean and is quickly becoming too saline even for tilapia, the durable African imports that were introduced to the Salton Sea in the 1960s. Hurlbert estimates that in another five to ten years it will be too salty for tilapia, the primary food for fish-eating birds at the Salton Sea. When the fish go, invertebrates will become more abundant, a boon for the birds who eat them. But a disaster for the millions of birds, including pelicans, who have become so dependent on the fish. And where will the Salton Sea's fish-eating birds go? In roughly the same period that millions of Pacific Flyway birds have come to rely on the Salton Sea and the marshes that surround it for food, rest, and reproduction, more than nine-tenths of southern California's wetlands have been transformed into agricultural lands, housing developments, or other bird- unfriendly uses. The creation of the Salton Sea has been a kind of accidental mitigation for the loss of other wetlands. If it becomes unusable to migrating and resident birds, many of them would have nowhere else. When I reach the mouth of the New River hundreds of white pelicans are wading in the shallow water off the salt encrusted shore. Around them swirl huge masses of gulls and sandpipers. The entire sky is vibrating with their beating wings. I see what I think is a wood stork. Is that an ibis? All at once the pelicans decide to move a few hundred yards down shore. Their wings and feet whack and drag against the water, making a strange and hollow sound. As what looks to me like a peregrine falcon shoots by I hear a crunch from my foot and look down to see I've stepped on one of what must be thousands of dead tilapia that line the salt-glowing beach. My overheated head is bombarded by two contradicting realities. I am in a wildlife paradise of human creation, an inadvertent gift of apology from humankind to birds. And I can't remember having seen anything more beautiful. But a few yards from me the fetid New River pours poison into its midst. A few miles from here the Alamo River deposits pesticides and concentrations of selenium that break federal standards for wildlife protection. Every day the water gets saltier and saltier. Is it inevitable that this "gift," this "mitigation," will prove to be a time bomb? Have we seduced these millions of birds here only to poison them? Was this summer's epidemic the first crack in the slow-motion explosion of this ecosystem? The heat has gotten to me. I am in a catastrophic state of mind and am prematurely mourning the loss of this place. Perhaps a long-shot, $110 million scheme of the Salton Sea Authority's to exchange water with the Gulf of California will work out and lake water quality will stabilize. (But what about the endangered harbor porpoise that lives in the Mexican waters that would receive the Salton Sea's contaminated water?) Or maybe the Salton Sea Authority, made up of local governments and irrigation districts, will succeed with a competing, $100 million plan to cut the lake in half and make a salt pond out of one part and keep the other at current salinity levels. Though that won't alleviate the selenium and pollution problems, it might keep fish in the lake for a few more decades. I'm out of drinking water and so I behold this fantastic place for a few more minutes and head back. Trudging along the New River and wishing the birds had brains enough to stay clear of it, I look up and see two people on the opposite bank, casting their lines into America's dirtiest river. Gordy Slack is Associate Editor of California Wild. |
Winter 1997
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