"Sea lice killing off wild salmon"

Researchers have new evidence that as the density of salmon farms increases, they can drive nearby wild salmon runs to extinction. The problem is sea lice, a natural parasite that normally attaches to adult salmon with little ill effect and has little contact with vulnerable juvenile salmon. All that changes, however, when fish farms move in.

A study in the journal Science to be published Friday shows that sea lice infestations around salmon farms in British Columbia's Broughton Archipelago have reached a density so high they are killing juvenile wild pink salmon at a rate fast enough to drive local runs to extinction in eight years if nothing is done — and four years have already passed.

"We've seen sea lice infestations on juvenile salmon in Norway, Ireland, Scotland and Canada, but it's been unclear and very contentious what the impact of the sea lice is on the wild salmon population," said Martin Krkosek, lead author of the study and a doctoral candidate at the Center for Mathematical Biology at the University of Alberta.

"What's really new and exciting about this paper is this is the first time scientists have had enough detailed data to actually measure the impact of sea lice on wild salmon populations," he said.

Principally funded by the Canadian Natural Sciences and Engineering Research Council, the peer-reviewed study is the latest in a series by a group of scientists trying to push the Canadian government to place more strict regulations on salmon farms to control sea lice.

Based on government stream surveys, the study used a computer model to analyze pink salmon returns in 64 rivers without exposure to salmon farms and seven rivers where young fish must migrate past at least one salmon farm. The study considered returns before and after sea lice infestations were noticed in wild fish in 2001....

When fish farms move in, hundreds of thousands of adults are raised in floating net pens anchored year-round in the channels where the young fish migrate. The study suggested that the density of fish farms reached a tipping point in 2001 that triggered a killer sea lice infestation.

Alexandra Morton, a co-author and director of the Salmon Coast Field Station in the archipelago, said wild salmon are surviving commercial fishing but not sea lice...