Extinction threat to wild pacific salmon

Parasites from aquaculture farms affect wild salmon in Canada

Wild pink salmon around the Broughton Archipelago are declining rapidly and will die out within 10 years if no action is taken, say researchers. They say the data, published in Science, raises serious concerns about the global expansion of aquaculture. Sea lice from farms [aquaculture farms - Mod.TG] are known to infect wild salmon, but until now the impact on wild populations has been uncertain.

"The impact is so severe that the viability of the wild salmon populations is threatened," said lead researcher Martin Krkosek from the University of Alberta in Edmonton, Canada.

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 8 years or less.

Dr. Krkosek said the population growth rate was "severely depressed. It means that the probability of extinction is 100 percent and the only question is how long it is going to take," he told BBC News.

Natural parasites: 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 report in Science has implications for other parts of the world where salmon is farmed, such as Norway and Scotland. Other species of salmon are known to become infected with sea lice, but they vary in their ability to withstand this.