A new study from British Columbia linking farmed salmon to dangerously high sea lice infections in wild juvenile stocks has refueled an intense, decade-long debate in Canada and Europe.

Similar disagreements about the study exist in Maine, but the debate seems overshadowed by a drop in active salmon farming, continued declines in wild Atlantic salmon populations, and little information about the relationship between them.

The subject has never been studied in Maine.

Near extinction, the species received federal protection in eight Downeast rivers under the Endangered Species Act in 2000.

The plight of wild Atlantic salmon is and has been “death by a thousand cuts,” observes Wayne Shaw, director of Downeast Salmon Federation, which aids salmon rescue efforts in Washington County. “When you look at the full picture ranging from water quality issues, dams, and aquaculture, among other things, the sea lice threat is another cut.

“I’m not certain there’s enough research to quantify the level of risk,” adds Shaw, “but it’s certainly relevant in Maine.”

Researchers from the University of Alberta measured sea lice loads on out-migrating juvenile pink and chum salmon and found they were 73 times higher than normal near a salmon farm and “exceeded ambient levels for 30 km (19 miles) of the wild migration route” after passing the farm.

Juveniles or “smolts” bore almost no sea lice before reaching the farm, according to the study, published in the British science journal Proceedings of the Royal Society B.

Sea lice are crustacean parasites that also feed off the skin, flesh and blood of salmon and other fish. They exist naturally in salt water but heavy infestations can be lethal to salmon. Smolts are extremely vulnerable to parasites and pathogens as they make the transition from freshwater nursery grounds to salt water.

Sea farmers use animal husbandry methods and medicines to prevent or reduce lice outbreaks in pens where millions of Pacific and Atlantic salmon species are raised to supply growing consumer demands for fish.

The scientists monitored 5,500 smolts along a 37-mile migration route in a fjord in the Broughton Archipelago in British Columbia. The fjord allowed them to study the impact of one active salmon farm anchored inside the route. The three-inch smolts were examined by hand every one-half to two miles.

Co-author John Volpe, now at the University of Victoria, said the data is transferable to Atlantic salmon in North America and Europe where “farms concentrate huge numbers of fish in a small area” and can affect wild fish.

“In a wild environment, fish are exposed to any pathogens in water. Now you’ve got such an incredible density of fish that a pen becomes a giant nursery of contagion that is passed back onto the wild.” Sea lice around the farm, which met industry management standards, were 33,000 times higher than ambient levels, he stressed. Miles below the pens, lice reproduced on surviving smolts and they infected a second school of juveniles that did not pass a farm.

Andrew Dobson, an epidemiologist from Princeton University, praised the study, according to a press release. “We’re seeing similar effects in Scotland, Norway and Ireland,” said Dobson, who is unconnected to the study.

Lice are not the only problem contributing to wild stock crashes, says Volpe, citing overharvesting as a major factor in Atlantic salmon declines. But adverse ecological impacts from aquaculture are so far-reaching that the industry “has driven wild salmon species to the brink of extinction” and created enormous socio-economic costs, such as increased suicides among Alaskan fishermen and in BC,” he stressed. “They cannot coexist: They are mutually exclusive.

“We can eliminate the problem tomorrow by putting pens on land or in floating, closed-containment systems, which would be costly. Or, at the very least, to separate them so they don’t interact.”

Maine’s proactive approach

Clustering farms together allows operators to coordinate harvests and restocking cycles to reduce parasites and other health threats, explains Samantha Horn Olsen, aquaculture coordinator for Maine’s Department of Marine Resources. Maine growers employ proactive pest management practices, including routine monitoring to treat lice outbreaks quickly, and routine fallowing to remove lice before restocking pens, she said.

“Narrow fjords and heavy sea lice burdens on farmed fish are two problems we don’t have,” adds Olsen.

Enrollment in Maine’s voluntary and federally subsidized Integrated Pest Management (IPM) program is required in order to participate in an Infectious Salmon Anemia (ISA) surveillance program, which is required to get indemnity for ISA outbreaks.

In 2001, prior to IPM, more than two million penned salmon were destroyed due to the disease, which can infect wild stocks.

Of 40 leased aquaculture sites in Cobscook Bay, where salmon farming is most concentrated, one-half to a dozen salmon farms are currently active, Olsen notes.

Farmed salmon prices remain at historic lows due to market saturation from Chile and Norway and leave thin profit margins for other growers.

“Maine’s salmon farming industry has fallen from $100 million in 2000 to $30 million,” explains Sebastian Belle, executive director of the Maine Aquaculture Association. He blames the loss on “environmental groups that have politicized salmon farming.”

Belle criticized the methodology and findings of the BC study, adding that researchers did not properly identify the lice they examined and failed to establish a cause-and-effect link between farmed and wild stocks. “Pathogens and parasites come from the wild, not from the farms.” Moreover, he said, scientific studies have never linked population density to contagion.

In addition to using proactive management practices, he stressed, “We have very strict environmental regulations we have to comply with, and we’re monitored by two state agencies and one federal agency.”

The industry has also engaged in cooperative management strategies with bordering New Brunswick salmon farmers whose harvests, said Olsen, are seven times greater than Maine’s.

Maine and Canadian farmers are not required to report sea lice counts or outbreaks in pens.

“Reporting those numbers would help government, industry, and [non-governmental organization] managers determine if they are a problem and to find solutions,” explains Jonathan Carr, a fisheries biologist for the non-profit Atlantic Salmon Federation (ASF).

Referring to a broader ASF study in New Brunswick’s Magaguadavich River, Carr said he noticed significantly less sea lice on adult salmon after farmers began using “Slice” (emmamectin benzoate) to control the parasite.

Slice is a neurotoxin that prevents lice from shedding skin and growing, Volpe explained. “It’s salmon chemotherapy that takes out shrimp, crab, any crustacean. Right now, it’s the only option.”

Adds Carr, “Bear in mind that we were dealing only with the survivors that made it back to the river and were able to climb a fish ladder. [Juveniles] are far more susceptible to lice, predators, water conditions; [lice] seem to be one more nail in the coffin.”

The ASF estimated that farmed Atlantic salmon outnumbered wild stocks 48-to-1 in 2003. Wild stocks breeding with genetically altered aquaculture escapees and health risks posed by ISA remain federal concerns that will be addressed in Maine’s Atlantic salmon recovery plan, expected to be issued soon by the National Oceanographic and Atmospheric Administration (NOAA).

Despite intense stocking efforts in federally protected rivers, less than one percent of fish are returning, according to NOAA’s regional fisheries biologist, Dave Bean. “We’re seeing some very small successes,” but biologists are just beginning to study and deal with basic threats, such as high acidity in natal rivers, that jeopardize salmon survival.

Citing lack of scientific data in Maine, he said, “Sea lice are not a major consideration in the recovery plan.” A future study is possible in Cobscook Bay, where wild salmon pass farms as they migrate to and from the ESA-listed Dennys River.

“Use very good husbandry practices”

“[Salmon farmers] don’t want to have an effect on wild fish,” explains David Rideout, executive director of the Canadian Aquaculture Industry Alliance in Ottawa. “We don’t believe we have an effect on the run,” he added, referring to the BC study.

Rideout points to criticism of the study by the Association of Aquaculture Veterinarians of British Columbia, and said he would “wait and see” what other studies reveal.

Borne out by efforts to rescue near-extinct Atlantic and Pacific stocks, Rideout explained that salmon are highly sensitive and react quickly to any stressors. “The best thing we can do is to use very good husbandry practices to produce and maintain healthy fish. It’s in our interests to do that.”

He believes salmon farms “can be part of the solution for stocking in rivers…. We have all the capacity to be able to help in their recovery.”

“No one knows the spatial aspects of this – how lice or pathogens [from farms] dissipate in the environment – where or how these might impact other species that we know little to nothing about,” Volpe emphasized.

As the price of salmon continues to drop, he predicts, industry profits will remain razor-thin and exert more pressure on farmers to produce larger numbers of fish – and there will be more pressure on wild stocks.

The study is available on-line at www.math.ualberta.ca/~mlewis/publications/SeaLicePub.htm.