Fish farm pest killing scores of salmon: study

Keith Gerein
CanWest News Service; Edmonton Journal
Tuesday, October 03, 2006

EDMONTON - Wild salmon migrating to the open ocean are being killed off at an alarming rate by sea lice produced by West Coast fish farms, new research from the University of Alberta suggests.

In some instances, the parasites are massacring up to 95 per cent of juvenile fish swimming through inlets where farms are located, says the study, published this week in the scientific journal Proceedings of the National Academy of Sciences.

Martin Krkosek, the study's lead author, said the findings represent the most definitive proof to date of the damage British Columbia's fish farms are wreaking on wild salmon stocks.

''It appears the scale is much, much larger than people had anticipated,'' said Krkosek, a PhD student at the university's Centre for Mathematical Biology.

''Salmon naturally have very large fluctuations in their abundance. So if you get a naturally poor year for salmon and then you add in the impact of sea lice on top of that, that extra bit of mortality could be enough to put the wild populations into real trouble.''

Previous work from the researchers indicated lice produced by the fish farms was extensively infesting young, wild salmon. What was not measured was the impact of that infestation.

In their new study, the scientists found just one or two lice is often lethal to juvenile salmon, which have not had time to bulk up and build resistance to the parasites like adult fish.

The lice kill by literally eating the young fish alive. They feed on the salmon's skin, mucus, muscle and blood, creating wounds that make it difficult for fish to maintain its saltwater balance.

Those that manage to stay alive are left in a weakened state and vulnerable to other predators, Krkosek said.

For years, fish farm industry leaders, as well as officials in the B.C. and federal governments, have argued there is no clear proof the farms are a source of lice outbreaks in wild salmon.

The new study took place over two years, and looked at the impacts on two different species of salmon along three migration routes.

A total of 14,000 salmon were sampled, using a new technique that allowed researchers to determine the number of lice attached without killing the fish in the process.

The study found an increasing number of salmon were dying over the spring migration season, with the highest mortality occurring in late spring when the sea lice population is higher.

The study's findings could be a big blow to B.C.'s fish farm industry, which is planning further expansion.

Krkosek said the parasites can be partially controlled on the farms with anti-lice treatments that are added to the fish food.

However, a better approach would be to relocate fish farms away from the mouths of rivers and along narrow migration corridors. This would allow small salmon a better chance of reaching the open ocean before encountering lice, he said.

kgerein@thejournal.canwest.com