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Monastersky, Richard
The Hidden Cost of Farming Fish
Chronicle of Higher Education #51, Issue 33, pA18-A21 4/22/2005

Will environmental problems deep-six efforts to raise salmon and other fish?

Two years ago Martin J. Krkosek escaped from his stuffy academic office and went fishing in the inky blue channels along the coast of British Columbia. But unlike most anglers, who dream about landing trophy specimens, Mr. Krkosek was hoping to catch some of the smallest fish in the water. And the sickest.

As a graduate student in mathematical biology at the University of Alberta, Mr. Krkosek wanted to know whether salmon farms can transfer diseases to wild populations. What he found on his fishing expedition has unsettling implications for salmon farmers, government officials in several countries, and the tens of millions of consumers who are increasingly adding farmed fish to their dinner menus.

Last month Mr. Krkosek and his colleagues reported the results of their study, which examined wild fry swimming downstream on their way to the open ocean. Their migration route passed a salmon farm, where upward of a million Atlantic salmon are kept in net enclosures.

Before reaching the farm, only about 5 percent of the young wild salmon were infected with a parasite called sea lice, which attaches to the fish's skin and eats holes in its flesh. But after the fry passed the farm, the rate of infection soared.

Each baby salmon--some only a few days old--carried on average two sea lice. By literally consuming the salmon in search of a blood meal, the lice grew quickly, sometimes reaching a third the size of the young fish. "It's like you or I having a 50-pound parasite on our back," says Mr. Krkosek. The lice infection rates, he says, "are a lot larger than people previously believed."

"These fish are encountering the lice during the most vulnerable stage in their life cycle, and so you'd expect then that the impact of the lice on these fish would be the most severe during this time," he adds.

Representatives of the salmon-farming industry and some scientists dispute or play down those findings. But the new study and other academic investigations are raising questions about the environmental harm caused by fish farming, which has grown rapidly in the past decade.

Salmon production, for example, quadrupled between 1992 and 2002, and companies are starting to ramp up efforts to farm other fish, such as Atlantic cod, halibut, and bluefin tuna. The United States is planning to expand the $1-billion domestic aquaculture industry to five times its current size, hoping it can erase some of the nation's nearly $8-billion-a-year trade deficit in seafood.

Right now, more than a third of the fish we eat comes from farms, and experts predict that aquaculture will outstrip fishing harvests in 5 to 15 years. "We're talking about the future of food production," says Daniel D. Benetti, an associate professor of aquaculture at the University of Miami, who is helping develop improved aquacultural techniques.


Salmon farming represents only a small percentage of the 50 million metric tons of aquacultural products harvested each year across the globe. Seaweed is the single biggest crop in worldwide aquaculture, and 95 percent of farms that raise fish are producing freshwater species like tilapia and carp in Asia, and catfish in the United States.

But carnivorous finfish--and salmon in particular--are the cash crops of the industry. They fetch higher prices and end up on the plates of consumers in the industrialized world. With few exceptions, the salmon fillets that glisten on ice at any supermarket in the United States are imported products from fish farms in Canada, Chile, Iceland, Norway, and other countries.

The 1.2 million tons of salmon farmed each year make a good fit with American consumers' desires and diets. Health-conscious consumers have followed their doctors' orders to eat more fish, especially those high in beneficial omega-3 fatty acids, such as salmon. And buyers have come to expect fresh fish throughout the year with consistent taste, texture, and appearance. Only fish farms can provide such uniform products.

Environmental groups and some scientists have challenged the fish-farming industry, however, charging that salmon operations can cause widespread ecological harm. Carnivorous fish like salmon, for example, consume three pounds of smaller fish for every pound of aquacultural product, a requirement that can deplete stocks of sardines, anchovies, and other smaller species that help anchor the marine food chain.

Escaped salmon pose another concern. Each year millions of salmon escape from pens around the world, competing with native fish for resources. They often interbreed with wild fish and reduce the strength of threatened populations.

And disease can run rampant through farm populations. "When you have a salmon farm, which in British Columbia includes upwards of a million fish in one pen, that's a smorgasbord for a parasite," says John P. Volpe, an assistant professor of marine conservation at the University of Victoria, in British Columbia, who collaborated on the sea-lice study.


The researchers conducted their work by hauling in samples of pink and chum salmon every few kilometers along Knight Inlet north of Victoria Island during the spring migration of wild salmon. They used magnifying glasses to count the number of parasites on 5,500 randomly selected salmon both upstream and downstream of a fish farm run by Stolt Sea Farm, a multinational company based in Norway that produced 61,300 tons of salmon in 2003.

The researchers developed a mathematical model taking into account the sampling results and locations, as well as the life cycle of the sea lice, which grow through three different stages. After plugging in the data, Mr. Krkosek's team determined that the farm was producing parasites at 30,000 times the natural rate, and spreading the lice vast distances. Near the salmon farm, sea lice reached 70 times their expected levels and the population of parasites remained elevated more than 18 miles downstream, the researchers report in the Proceedings of the Royal Society B in late March. (Stolt Sea Farm did not return several calls requesting comment on the study.)

Other studies in Europe and Canada have consistently shown more sea lice near farms than away from farms, says Mr. Krkosek. But the new study is the first to collect such detailed parasite samples and use those to compute what the natural rates of disease would be in the absence of the farm, he says.

David Rideout, executive director of the Canadian Aquaculture Industry Alliance, disputes the new assessments, saying that farmed salmon get their parasites from wild fish. "We put healthy, safe animals on our farms," he says. "When we find sea lice, we take action. It's an issue that we don't like to have on our farms. But it is a phenomenon of the wild salmon. I would say there's no huge pool of sea lice on our farms."

Mr. Krkosek agrees that the farms do not introduce the parasite into the water. "But having salmon farms in the near-shore environment provides a huge year-round population for the lice to live on and grow on. Those are ideal conditions for parasites to thrive," says Mr. Krkosek, who received support for his study from Canada's science-research council and also from environmental groups critical of salmon farming in British Columbia.

Normally, lice populations would drop markedly during the winter in this region because there are few wild adult salmon there at the time. So when the eggs hatch in the spring, young salmon swimming downstream would rarely encounter lice in the absence of farms, he says.


Even though aquaculture companies give fish an antiparasitic drug called Slice, they must cease the treatments for several weeks before harvesting the fish, so that the salmon will clear the medication from their system. That provides a window for the lice populations to rebound, says Mr. Krkosek.

"When you have millions of farmed salmon in the water, even a low load of lice per salmon can still impose a large infection pressure" on the wild salmon, he says.

He and his colleagues propose that government regulators reconsider permitting the use of large open-net aquaculture in wild-salmon habitats. "There is a clear potential for severe and irreversible damages to be inflicted upon wild salmon populations and their dependent cultures, ecosystems, and economies," they wrote in a statement.

Brian E. Riddell, who oversees research on sea lice for the Department of Fisheries and Oceans, in Canada, says the new model developed by Mr. Krkosek provides strong evidence that salmon farms can transfer lice to wild populations. Regarding lice populations, he says, "it would certainly indicate there is a spike in the location of the farm."

For several years, environmentalists have charged that lice are already harming wild salmon. In 2001, for example, sea lice were detected on juvenile pink salmon in British Columbia's Broughton Archipelago, north of Vancouver Island. The next year only 150,000 adult pink salmon returned to the region to spawn, compared with five million spawners two years earlier, says Mr. Riddell.

But the evidence is so far equivocal on how the lice affect salmon, he says. When the department has collected fish samples and compared infected fish versus clean fish, "you don't see any evidence of a significant effect of lice on the fish you sample," he says. The fish with lice seem to be growing at the same rate as those without lice. The obvious gap in that observation, he notes, is that any fish that have died because of a lice infection would not show up in the sampling.

So the department is now starting a research program in the laboratory to investigate whether lice can harm juvenile pink and chum salmon.


Parasites and other diseases are only a part of the threat posed by salmon farms, contends Mr. Volpe of the University of Victoria. He has studied what happens when fish escape from salmon farms and start to compete with wild populations.

For many years, government officials and the salmon industry contended that escapees would not survive in the Pacific because most farms raise exotic salmon from the Atlantic. Mr. Volpe has tracked previous claims that play down the issue. He quotes a 1987 document, issued by the province of British Columbia, as saying that farmed Atlantic salmon, "have no home stream to return to in order to spawn. Instead, they would return (if they survived that long) to their home fish farm. Without a freshwater spawning ground, they would be unable to reproduce."

Without looking very hard, however, Mr. Volpe found populations of Atlantic salmon in three rivers on Vancouver Island, with hundreds of juveniles, indicating that the animals were spawning. The juveniles were different ages, which suggests that escapees had spawned in more than one season.

No one has yet found evidence that Atlantic salmon have established a self-sustaining population in the Pacific--one that returns year after year to the same home stream. But Mr. Volpe argues that nobody is looking. "There is no active program going on to determine how many escapes are occurring, are they surviving, and where are they colonizing."

In the Atlantic Ocean, the issue of escapees poses even more of a threat because salmon from farms can interbreed with native fish. With populations of wild salmon so depressed--they are endangered along the northeast coast of the United States--the escapees are starting to rival the native fish in numbers.

Officially, only about one in 1,000 fish escape from farms. But Norway, Scotland, Denmark's Faroe Islands, Iceland, and Canada all produce so many salmon that some two million fish escape into the Atlantic each year, says Ian A. Fleming, an associate professor of ocean sciences at Memorial University of Newfoundland. The escapees represent more than one-quarter of the salmon swimming in the Atlantic, he says.

In some rivers along Norway's coast, the proportion of escapees approaches 80 percent of the salmon, says Mr. Fleming, who has conducted research there. In one experiment, his team blocked off access to the river Imsa in southwestern Norway and introduced both farmed fish and wild fish. They allowed them to breed and looked for the offspring, testing how efficient each group was in reproducing. Farmed fish turned out to be genetically less fit; they were less successful at breeding and surviving than the wild fish.

Given the large numbers of farmed fish that escape, however, their genes are spreading at a rapid pace. "The wild populations are becoming more and more farmlike through time," he says. Wild fish will become 50 percent more like farmed fish in as little as 10 generations, or 40 to 50 years, he calculates.

That is bad news for the wild populations because the traits of farmed fish will not help the population thrive in the wild, says Rebecca J. Goldburg, a senior scientist at Environmental Defense, a New York-based environmental organization. "It's a bit like interbreeding a domesticated dog with a wolf. The result is something that isn't as fit to survive in the wild," says Ms. Goldburg, who published a study with Rosamond Naylor of Stanford University on the fish-farming industry in January in Frontiers in Ecology.

Salmon producers contend that escapes are a problem of the past. "From the perspective of industry, we've got that issue resolved," says Mr. Rideout of the Canadian Aquaculture Industry Alliance. "It's a very rare occurrence when salmon escape," he says.

But Mr. Volpe of British Columbia says that "the public here is being willfully misled. There's a certain amount of willful ignorance that has led to the conclusion that there are no escapes."

Farms in British Columbia, he says, have reportedly decreased the rate of escapes in 2003 to 0.1 percent of what they were only two years earlier. But many of those farms are run by the same companies that operate farms in other parts of the world, using the same techniques--where the numbers of reported escapes have not dropped appreciably.


In the tropical waters off Puerto Rico and the Bahamas, scientists are trying to develop aquaculture techniques that avoid many of the problems that have emerged elsewhere. Mr. Benetti, of the University of Miami, has been working with two private companies, Snapperfarm Inc. and AquaSense LLC, to demonstrate the potential of siting cages in the open ocean well below the surface.

Unlike traditional farms, which are located in bays or channels and have pens open at the surface, the experimental enclosures sit a mile or more offshore in 100 feet of water. Looking a bit like flying saucers hovering underwater, the totally enclosed pens have tops that reach a depth of 40 feet so they won't interfere with passing boats. And a steady current of up to 1.2 knots sweeps through the nets.

"You have 600 million gallons of free-flowing clean water running through those cages daily," says Mr. Benetti, an ardent advocate of open-ocean farming, who described his work in February at a meeting of the American Association for the Advancement of Science, in Washington. The advantage of farming in this locale is that currents wash away pollution and disease organisms, diluting them so they don't threaten the farm fish or native populations, he says. "By moving offshore, we will diminish dramatically the likelihood of disease outbreaks and pollution to occur."

In theory such submerged nets should cut down on escapes as well, since the pens are closed at the top and are well below storm waves. "The system has a proven record," he says. "Last year in the Bahamas, Hurricane Frances stayed on the top of this site with winds over 100 miles per hour for 24 hours, with no damage to the cage or the fish. If it was a traditional system, the cage would be gone," he says.

At present, however, the demonstration project has not shown that the submerged systems can earn a profit. And Mr. Benetti is now battling sharks. In one case, a shark attacked a full pen, ripping a hole in the mesh and letting $500,000 of fish escape.

The Florida researchers are working with engineers to develop systems that will keep sharks away from the pens. "We will overcome this hurdle," says Mr. Benetti. "This is not going to stop us."

The National Oceanic and Atmospheric Administration apparently agrees. The agency sees offshore aquaculture as part of the nation's future, one way for the country to markedly increase its production of fish and other marine products. NOAA is currently drafting legislation that would grant it the authority to issue permits for offshore aquaculture.

But critics remain unconvinced that farming salmon and other carnivorous fish provides a net advantage for the environment, given the problems that have come to light in the past. Many times, industry swims ahead far faster than the researchers who are monitoring it, says Mr. Volpe. "This Wild West attitude that we seem to be going down with developing aquaculture as fast as humanly possible, and to the greatest magnitude possible, is just rife with examples of the shortcomings of science."

PHOTO (COLOR): Several sea lice, which appear as dark spots, infect a juvenile wild salmon caught in the waters off British Columbia.

PHOTO (COLOR): The Broughton Archipelago in British Columbia has 126 licensed salmon farms, where millions of fish are raised in open-top nets. The farms are also breeding grounds for parasitic sea lice, which can infect wild fish.

PHOTO (COLOR): In a demonstration project off Puerto Rico, researchers are developing underwater fish pens suitable for use in the open ocean.


By Richard Monastersky

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