Fish Farming destroying wild stocks

Fish farming as it’s currently practised in Canada is destroying wild salmon stocks and threatens to completely wipe them out within four years in one area of British Columbia, according to new research.

Although debate over the environmental impact of fish farms has raged for years, a study published Thursday in the journal Science leaves little doubt that aquaculture can damage wild populations by infecting juveniles with fatal parasites, said Martin Krkosek of the University of Alberta.

“This is the first time we’ve been able to quantify the effects of the sea lice on wild salmon,” he said. “The impact is severe.”

Mr. Krkosek said that unless something changes, the Broughton archipelago ,about 240 kilometres northwest of Vancouver, will lose its once-abundant wild salmon runs within four years. The findings have implications for fish farming around the world for all species, he said.

“The current model for farming salmon is the same model that’s been used to farm other species like cod and halibut. This is kind of a bellwether case for aquaculture in general.”
Salmon spawn in fresh water but live their adult lives in the ocean, a life cycle that forces juvenile salmon on their way back to the sea to swim past salmon farms. Parasites such as sea lice thrive in the farms, which can contain over a million fish within net pens.

Previous studies have linked fish farms to increased sea lice infestation in nearby wild stocks. But because young salmon have such high natural mortality, it was never clear if parasites were actually reducing wild stocks.

“The argument has been, ‘Who cares if some of the salmon are infected with sea lice, because most of them are going to die anyway,’ ” Mr. Krkosek said.

The new research answers that question by analyzing federal data that estimates populations in the archipelago and just to the north of it. The archipelago is now home to more than 20 farms along an 80-kilometre stretch of salmon run. None exist in the northern region.

From 1970 to 2001, both study areas were about equally productive. Both supported commercial fisheries.
But after their first major sea lice infestation in 2001, wild stocks in the Broughton archipelago began collapsing and have now shrunk by 80 per cent. Stocks to the north have held steady.

“It’s quite dramatic,” said Mr. Krkosek. “We were expecting to see an effect, but not as strong as we’ve actually measured.

“Based on the rate of decline we have seen, those pink salmon populations are going to go from their historical level to extinction in four generations. Right now, we’re already halfway through that decline.

“There’s four years left before these fish are gone if the sea lice infestations continue.”
Sea lice occur naturally and adult salmon infected with a few of them can stay healthy. But researcher Alexandra Morton says juvenile salmon — which don’t yet have scales and are only a few centimetres long — aren’t strong enough to withstand the heavy exposure to sea lice they must endure on their way back to the sea.

“This is a fatal collision between the parasite and the host,” she said. “It’s very common to see sea lice eating holes, causing open wounds in the little fish.”
Although pink salmon are most vulnerable, other salmon species suffer similar effects, Ms. Morton said.

Wild salmon are a crucial part of the entire coastal ecosystem, providing essential food for eagles, bears, wolves and whales, she pointed out.

A 2002 report from B.C.‘s auditor general found that wild salmon are worth more than $600 million to the provincial economy. Recreational and commercial wild salmon fisheries provided nearly 4,600 jobs.

“The most obvious thing to do is move the salmon farms out of the way,” Mr. Krkosek said.  “Don’t put the farms on migration routes, don’t put them near spawning rivers. Maybe putting them offshore is a good place.”

Aquaculture is an increasingly important industry in B.C. and around the world as global demand for fish outstrips the capacity of wild stocks.

B.C. alone has 741 aquaculture operations for both shellfish and fish, mostly salmon. The industry produced 88,100 tonnes of fish and shellfish worth about $430-million at the farm gate in 2006.

It employs about 3,000 people, most in small coastal communities.

That success is part of the problem, said Mr. Krkosek.  “If there are only a couple of farms, only a couple hundred thousand fish in the water, we probably wouldn’t have a problem at all. But now we’ve just got millions and millions of salmon in net pens that aren’t supposed to be there and it’s really changing the dynamics of disease.

“The industry has reached a sufficient size to really be very damaging to wild fish populations. Sea lice are just the tip of the iceberg. There’s viral and bacterial diseases that are really hard to track and most likely there’s other things happening as well.”

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