Auteur: Henk Tennekes

At first the biologists noticed something unusual about the dead fish washing up on the shore of the Salton Sea: All of them were fully grown, at least 7 inches long. There were no smaller fish among the carcasses pushed ashore by the lapping waves. Then the biologists started seeing other clues in the birds. Western grebes, which normally arrive by the thousands to forage, were nowhere to be found. Thousands of Caspian terns would normally stop off to nest, but they were also missing. And only small numbers of eared grebes, with their distinctive black heads and yellowish tufts behind their eyes, bobbed in the water. Hundreds of other eared grebes washed ashore dead earlier this year, their emaciated bodies indicating they starved.

The lack of small fish and the sudden declines of some bird species at the Sonny Bono Salton Sea National Wildlife Refuge could be signs that the lake’s overburdened ecosystem is starting to unravel and deteriorate. Scientists have been predicting for years that rising salinity will eventually render California’s largest lake inhospitable for even hardy tilapia, a fish introduced decades ago that has become a vital food source for birds.

The abrupt changes observed by biologists Chris Schoneman and Tom Anderson at the wildlife refuge suggest time might be running out for fish-eating birds such as pelicans that depend on the lake as a critical sanctuary. They acknowledge their concerns are based on speculation because comprehensive surveys of birds and fish haven’t been carried out in years. But Schoneman said in his 12 years working at the wildlife refuge, he has never before witnessed symptoms like those that have appeared this year.

“Maybe we’re at the point where salinity is limiting fish reproduction,” said Schoneman, the refuge’s manager. “The impact on birds from having a repressed or eliminated fish reproduction capability out here is devastating. That means the productivity of the Salton Sea is drastically reduced.”

The lake, which lies 234 feet below sea level and is much saltier than the Pacific, is going through what scientists call a natural “aging process.” Because it has no outlet, the lake has been growing saltier with each passing year.

A decade ago in 2006, the Salton Sea’s salinity stood at 47 parts per thousand. Water samples this year show salinity levels of between 58 and 59 parts per thousand – near the estimated threshold of 60 parts per thousand at which experts have predicted the remaining fish might stop breeding.

The lake is also showing other symptoms of decay. It’s burdened by an increasing load of detritus and nutrients that have accumulated for years as farm runoff has flowed in and evaporation has taken its toll.

When windstorms sweep across the desert and churn up the water, the sea regularly burps out hydrogen sulfide, which smells like rotten eggs. Fish die-offs have left the shoreline littered with skeletons.

Anderson, the assistant manager of the wildlife refuge, said he used to see small juvenile fish among the dead tilapia washing ashore. But he hasn’t seen any small fish for quite a while. And birds such as western grebes and Caspian terns, which depend on small fish, have been largely absent.

This spring, Anderson noticed eared grebes weren’t out in the sea where he expected to find them. Instead, the few birds he saw were congregating around drains and pools of freshwater alongside the shore. He said the birds appeared unhealthy and their feathers looked wet, suggesting they had stopped preening themselves.

“Then I started seeing dead ones in a lot of different areas, and looking at them, they were very emaciated,” Anderson said. “So we suspected they just weren’t getting the food resources they needed in the Salton Sea.”

Anderson saw a couple hundred birds dead on the shore. Extrapolating to the entire sea, he estimated a total of 1,000 to 2,000 eared grebes may have died.

The biologists sent some of the carcasses to a laboratory to determine the cause of death. The lab analysis turned up no signs of disease, poisoning or parasites, and concluded the birds starved to death.

Eared grebes normally feed on pile worms, diving down to the bottom to dig the worms out of the mud. Anderson said he thinks the die-off suggests the numbers of worms have probably dropped.

“Biologists who talk about the Salton Sea, they talk about a tipping point in the salinity, and these might be indications that we’re just about there, where the tilapia will disappear, pile worms will disappear,” Anderson said, “and both of those are big food resources at the Salton Sea.”

If they’re unable to find food, many more birds could abandon the Salton Sea and be forced to search for habitats elsewhere. Some of those fish-eating birds range from American white pelicans to herons, black skimmers and double-crested cormorants.

The drops in some bird populations appear significant and point to an urgent need to start creating habitat by building wetlands along the receding shores, said Andrea Jones, director of bird conservation for Audubon California. She said the changes observed by the staff at the national wildlife refuge suggest “conditions that we didn’t expect for a couple years are happening now.”

State officials plan to start building several thousand acres of artificial wetlands using canals to carry water from the New River and the Alamo River to areas of dry shoreline. The wetlands have a dual purpose: controlling hazardous dust as the lake shrinks and creating environments where fish and birds can survive. After years of inaction, California has budgeted $80.5 million for the Salton Sea projects this year.

Audubon California’s bird experts are developing a habitat plan for the state with recommendations of various habitat types, such as deep-water areas, shallow wetlands and marshes with reeds, and acreages that different groups of bird species will need. Jones said state officials should start building those wetlands right away because without intervention, the deterioration of the Salton Sea will add to the pressures on birds that are already struggling elsewhere.

The Salton Sea lies in a basin that over millennia has at times been a dry lake bed and at others has been a lake filled with water from the Colorado River. The sea was created in its current form between 1905 and 1907, when Colorado River water broke through irrigation canals in the Imperial Valley and flooded into the basin.

Since then, the lake has been sustained largely by runoff from farms. But the amounts of water flowing into the lake have been decreasing for years. And the Salton Sea’s decline is set to accelerate starting in 2018, when more water will be transferred from the Imperial Valley to San Diego County and the Coachella Valley under a water transfer deal.

During the past century, the Salton Sea has become a critical inland stop-off point for many birds along the Pacific Flyway. Some birds flock to the lake to nest. Others feed and refuel for their long migrations.

At the Sonny Bono Salton Sea National Wildlife Refuge, Schoneman said a total of 424 bird species have been spotted over the years.

If some of those birds eventually can’t survive at the Salton Sea, Jones said, it’s not clear where else they might go.

“That’s hard to think about because there aren’t many alternatives,” Jones said. “The fish-eating birds, we really don’t want to lose them because where are all these white pelicans going to go if they don’t have the Salton Sea to spend the winter in?”

Jones acknowledged that some people question whether it makes sense to intervene.

“An argument we hear even from some of our members is, ‘Why do you want to save any portion of the sea? It’s artificial. Those birds will go somewhere else,’” she said. “And our argument is that it doesn’t matter whether you think it was artificially created or not because a lot of the places in California these water birds used to use – like Tulare Lake – are gone.”

Wetlands that birds once relied on have been drained and left dry in places from the Central Valley to the Colorado River Delta.

“So the Salton Sea is their choice now. It’s their option,” Jones said. She said Audubon aims to organize sea-wide bird surveys in December and in the spring.

A comprehensive bird count for the entire Salton Sea hasn’t been done since 1999. A report on those surveys in 2000 estimated the total population of all waterbirds at between 434,000 and 583,000 in November and December. The surveys also found colonies with more 14,000 pairs of breeding waterbirds.

Jones said it’s now especially important to organize a new round of surveys to confirm the trends in bird populations.

As for fish, small tilapia can still be found in at least some parts of the lake. At the Salton Sea State Recreation Area on the north shore, tilapia have been successfully breeding in the harbor, said Kathy Dice, the superintendent of Anza-Borrego Desert State Park. Due to the small tilapia in the harbor, she said, people aren’t allowed to fish there.

“That particular harbor actually has some freshwater flowing into it,” said Tim Bradley, an ecology professor and director of the Salton Sea Initiative at the University of California, Irvine. “I have seen young fish there in abundance, but I think that could be an unusual habitat because of that freshwater input.”

Researchers haven’t carried out routine surveys of fish, pile worms or other invertebrates at the sea in recent years. Bradley and other scientists say they think it’s important for more surveys to be carried out now to better understand how the ecosystem is changing.

Doug Barnum, who heads the U.S. Geological Survey’s Salton Sea Science Office, said without routine monitoring, “the best anyone can provide at this point is speculation.”

“There have been previous episodes of large declines in the fish population, all of which have proved to be ‘false alarms,’” Barnum said in an email. He said the lack of small fish among the dead fish seen at the wildlife refuge isn’t surprising given scientists’ longstanding estimates of declines in fish when the salinity reaches about 60 parts per thousand.

“But unless some sort of monitoring of the live fish population is implemented,” Barnum said, “there is no way to ascertain the status of fish reproduction at the Salton Sea.”

As the Salton Sea grows saltier, scientists agree that sooner or later the collapse of the fish population is inevitable.

Decades ago, people fished for corvina in the lake. Then the corvina disappeared as the salinity kept increasing. Tilapia were introduced into agricultural drains near the sea a half-century ago to help control aquatic vegetation. Now the tilapia are headed the way of the corvina. What isn’t clear is how much longer some fish might hold on, and whether they’re hitting their limits now.

The declines in birds at the national wildlife refuge could be occurring due to dwindling populations of fish or other prey, or could be caused by other unrelated issues elsewhere on the Pacific Flyway, said Bruce Wilcox, assistant secretary for Salton Sea policy at the California Natural Resources Agency. He said the concerns raised by Schoneman and Anderson are valid, but the changes they’ve observed don’t necessarily mean the fish are disappearing just yet.

“We’re on borrowed time. If this isn’t the tipping point, it’s coming soon,” Wilcox said. “I think we need to move forward as fast as we possibly can to develop habitat.”

A task forced created by Gov. Jerry Brown last year has ordered state agencies to develop a plan for the sea and meet a short-term goal of carrying out projects to suppress dust and create habitat on 9,000 to 12,000 acres.

Wilcox said the funding in this year’s budget will help the state begin to move toward that goal, building a “backbone” of canals and several thousand acres of wetlands. He said the levels of salinity and nutrients will be managed to make the wetlands better habitat than what birds now find at the sea.

Not everyone is pleased with the idea of creating wetlands in the desert. John Rasmussen, a retired physician who lives in Palm Desert, said he’s concerned that flooding thousands of acres will create a perfect breeding ground for disease-carrying mosquitoes.

“To me, it represents a potential public health hazard,” Rasmussen said, noting that mosquitoes in the area have tested positive for West Nile virus and St. Louis encephalitis.

Source: The Desert Sun, August 9, 2016
http://www.desertsun.com/story/news/environment/2016/08/09/salton-sea-biologists-find-some-birds-dead-missing/88118480/