With fish crammed tightly into cages in open water, fish farming is an ideal breeding ground for disease and parasites, such as sealice. Escaped infected fish can then take these diseases with them into the wild and infect the non-farmed population.
Around half a million farmed fish escape into Norwegian waters every year, meaning one out of every four salmon or trout found in Norway's coastal waters are fish farm escapees. Large numbers of escaped farmed salmon have been reported in Scotland, in January 2005 alone over 629,000 farmed fish are known to have escaped.
Scotland ranks third in the global production of farmed salmon, the findings of this new report will strengthen widespread calls for more secure cages for farmed salmon in Scottish waters to reduce the possibility of escapees, even in extreme weather conditions.
"It's totally unacceptable that such enormous amounts of farmed fish have escaped from fish farms into open waters, undermining the long-term survival of wild salmon," said Maren Esmark, Marine Coordinator at WWF-Norway.
WWF's report also shows that the up-river migration of escaped farmed salmon late in the spawning season physically displaces the eggs of the already spawned wild salmon. This effectively means that wild salmon's reproduction ability is being reduced.
This rise in the number of escaped salmon has led to an increase in interbreeding between the two varieties, which dilutes the gene pool and threatens the survival rate of offspring.
With 500,000 tons of farmed salmon and trout produced per year, Norway's fish farming business is a cornerstone of the country's economy. However, Norwegian waters remain home to half of the global stock of wild Atlantic salmon.
"One third of Norway's wild salmon stocks are already suffering because of human activity," said Dr. Simon Cripps, Director of WWF's Global Marine Programme.
"Add to that the increasing threat of escaped fish and we have to ensure that industry and government clean up their act and begin to act responsibly."
WWF is also concerned about the increase in escaped farmed cod from Norway's expanding cod farming industry and the effects this can have on the already imperilled stocks of wild cod. Escaped fish, whether they are salmon or cod also represent an economic loss for the industry.
The Norwegian government and the fish farming industry have already taken some steps to reduce the amount of escaped fish, but more needs to be done.
These new measures should include increased security to prevent escapes, the individual tagging of farmed fish, and the location of fish farms away from vulnerable stocks of wild salmon or wild cod.
Source: World Wildlife Fund - 12th May 2005
WWF: Escaped farmed fish threaten wild salmon stocks
NORWAY - The increased number of farmed salmon escaping into Norway's open waters puts wild salmon under greater threat of disease, breeding difficulties and genetic contamination. A new WWF report shows that stocks of wild Atlantic salmon are already depleted due to the existing threats posed by dams and pollution.
Escaped farmed fish threaten wild salmon stocks - NORWAY - The increased number of farmed salmon escaping into Norway's open waters puts wild salmon under greater threat of disease, breeding difficulties and genetic contamination. A new WWF report shows that stocks of wild Atlantic salmon are already depleted due to the existing threats posed by dams and pollution.