Farmed Salmon Killing Off Wild Cousins
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Farmed Salmon Killing Off Wild Cousins
by Stephen Leahy
Canada's open-ocean salmon farms are killing enormous numbers of wild salmon, threatening the species, a new study shows.
Research published Monday found that sea lice -- a fish parasite -- from salmon farms along the British Columbia coast kill up to 95 percent of the wild juvenile salmon as they head out to sea.
"It is a startling conclusion," said Alexandra Morton, a biologist with the Raincoast Research Society and co-author of the study published in the Proceedings of the National Academy of Sciences.
"We are not going to have any wild salmon at this rate," Morton told IPS.
The study says there is little doubt that the source of the sea lice infestation is British Columbia's (BC) booming aquaculture industry, where tens of millions of Atlantic salmon are raised in open-ocean net pens along the coast.
"The debate is over," said Morton.
The impact of more than 100 large salmon aquaculture operations along the BC coastline has been bitterly disputed for the last decade. British Columbia is the world's fourth largest farmed salmon producer, netting more than 300 million dollars in annual sales, mainly to the United States.
The farmed fish are non-native Atlantic salmon, which are prone to infestations of sea lice -- small parasites that feed on the skin and mucous membranes -- which are not generally found in high numbers, except at fish farms where a million fish can be impounded.
Adult Pacific salmon live in the open ocean but fight their way up BC's many mountain rivers and streams to lay their eggs in the spring and fall before dying. Not long after hatching, these juvenile fish make their way back downstream to river mouths and inlets, where they encounter salmon farms and underwater clouds of sea lice.
The migration paths of juvenile salmon keeps them away from wild adult salmon, which are carriers of the lice, said report co-author Martin Krkosek, a Ph.D. student at the University of Alberta's Centre for Mathematical Biology.
"But farms are often in the worst possible locations," Krkosek told IPS.
Researchers tracked juveniles over 100 kilometres on their migration routes, sampling them every two kilometres. Sea lice were counted on more than 14,000 young fish.
"You could see how the infection progressed as they neared the farms," Krkosek said.
Sea lice can travel up to 50 kms to infect a host, according to new research at the University of Auckland in New Zealand.
Krkosek and his colleagues employed some sophisticated mathematical modeling to tease out whether the concentration of sea lice came from farms or other potential sources and were able to definitely identify the farms as by far the main source.
"The work is of an impeccably high standard, and will be very difficult to refute," said Andy Dobson, an epidemiologist from Princeton University who specialises in wildlife diseases.
"It ties up a lot of loose ends from other studies on sea lice and formally quantifies the impacts," Dobson said in an interview.
To determine the impact, mortality experiments were done with more than 3,000 fish.
"It takes only one or two sea lice to kill a juvenile pink or chum salmon," said Krkosek. "The juveniles are so vulnerable because they are so small -- only one to two inches long."
The final results show that lice from farms resulted in a nine to 95 percent mortality in several wild juvenile pink and chum salmon populations.
"Even the best case scenario of an additional 10 percent mortality from farm-origin sea lice could push a fish stock into the red zone," said biologist Dr. John Volpe, a study co-author at the University of Victoria.
"I think our study shows there are clearly severe problems with open-ocean salmon farms," said Krkosek.
Although this was the most detailed study ever done on the issue, experts knew or suspected that sea lice from farms were directly involved in the declines of wild fish in Scotland, Ireland and Norway, major centres of farmed salmon.
"They sacrificed their wild salmon for farmed," he said.
However, the situation is far different in BC, where entire wilderness ecosystems of the west coast are dependant on abundant wild salmon stocks.
"Salmon feed eagles, bears, whales, wolves and even forests here," Krkosek explained.
It is a remarkable ecological story that Pacific salmon spend two years feeding in the open ocean, then return to their natal streams and rivers to spawn and die. Many species feed on the dying or dead salmon and they also bring large quantities of carcasses into forests at the same time. The decaying carcasses enrich the soil and feed many plants, including the region's mighty red cedars and sitka spruce trees.
Researchers have found salmon nutrients inside the leaves at the top of 2,000-year-old trees, says Krkosek.
And the juvenile salmon don't feed until they reach the open ocean.
"Outdoor tourism is a major industry in BC, it is crazy to do anything that harms the pinks (salmon)," said Alexandra Morton.
Lice infestations can be reduced by treating farmed salmon with insecticides, but those chemicals hurt the shrimp, prawns and other organisms. And such treatments are expensive and lice can become resistant.
It is past time to put salmon aquaculture into a closed system so the industry will properly deal with its wastes rather than dumping them into the sea, Morton said.
That would be much more expensive, she acknowledged, but said the industry has been damaging ocean ecology while enjoying the benefits from ocean tides that flush out fouled net pens for free.
"The study will be a hot topic and undergo intense scrutiny," said Christina Burridge executive director of the BC Seafood Alliance, an industry association.
"Beyond that I can't comment without seeing the study," Burridge told IPS.
Whether the study will change how salmon aquaculture is done in BC is an open question.
In 2001, an outbreak of sea lice from farms in the Broughton Archipelago on northern Vancouver Island wiped out 99 percent -- estimated at 3.5 to 5 million -- of the native pink salmon runs.
Despite that fact, the BC government ended a seven-year moratorium on salmon farming expansion a year later.
The BC government has been in denial about the sea lice problem, says Morton.
Diseases and infestations are to be expected whereever there are large concentrations of fish in aquaculture or animals such as feedlots and factory farms, said Princeton's Dobson.
"When are we going to see the first human disease caused by aquaculture?" he asked.
Copyright © 2006 IPS-Inter Press Service