Fish: farmed or free?
Posted by Daniel Hall on December 14, 2007
Dr Krkosek and colleagues compiled data on the numbers of pink salmon in rivers around the central coast of British Columbia.
They compared populations of salmon that had come into contact with salmon farms with those that had not been exposed, from 1970 to the present day.
Using a mathematical model of population growth rates, they show that sea lice from industrial fish farms are reducing the numbers of wild pink salmon — a Pacific salmon species — to the extent that the fish could be locally extinct in eight years or less. …
Scientists say commercial open-net salmon farms are a “haven” for sea lice – naturally occurring parasites that attach to the skin and muscle of salmon.
Mature fish can survive being infested by a few lice but tiny juvenile salmon are particularly vulnerable to attack.
They come into contact with sea lice when they swim past fish farms on their migratory routes from rivers to the sea.
The actual study compiled data from 71 rivers where salmon migrate and spawn, including 7 rivers where salmon must migrate past at least one farm. The researchers found that from 2002 to 2006 the parasite-induced mortality rate among juvenile salmon exposed to lice along these rivers ranged from 16% to 97%, with mortality commonly over 80%. The BBC News article points out, however, that there are benefits to salmon farming, and there are ways to do it without putting wild salmon at risk:
Dr Krkosek said the impact of fish farms on wild salmon has been “an emotionally, politically and economically charged debate” in Canada.
“Salmon are considered a natural treasure to Canadians, but salmon farming has a lot of economic opportunity – we really need economic activity to supplement coastal economies where fisheries and other resource centres are not doing as well,” he explained.
“So there are economic benefits to having salmon farms, but the way that it is currently being done is very damaging to the environment and there are better ways of doing it.” …
“The most obvious thing to do is to move the farm out of the way of the wild fish,” Dr Krkosek told BBC News.
“Don’t put them on the migration route, and don’t put them near the spawning rivers. Another option is to move to closed containment technology where the net pen is replaced with a physical barrier that prevents the exchange of parasites – that would solve the problem too.”