The world's wild salmon population is being ravaged by sea lice infestation from fish farms, new Canadian research has confirmed.

Up to 95 per cent of young wild salmon that migrate out to sea die after swimming through plumes of lice from infected fish farms, according to results of the research, published this week in the Proceedings of the National Academy of Sciences of The United States of America.

"We know that fish farms raise sea lice levels, and we know that sea lice kill fish," said Martin Krkosek, the report's author and a mathematical biologist at the University of Alberta.

"This is the first study to estimate the total impact."

Krkosek was part of an international team of biologists, mathematicians and environmentalists that studied more than 14,000 juvenile salmon on a 60-kilometre migratory passage, past open-net fish farms off the coast of British Columbia.

They found that while young salmon carried almost no sea lice before reaching the fish farms, they became heavily infected as they approached them and swam through the plumes.

Post-mortems conducted on more than 3,000 juvenile fish concluded: nine per cent died in early spring when the sea lice population was low; 95 per cent were killed later in the season when sea lice numbers swelled.

The lice are not generally dangerous to adult salmon; but young salmon are at risk because their scales and outer tissue are not as strong in protecting vital organs against the lice, which feast on flesh and tissue.

"It takes only one or two sea lice to kill a juvenile pink or chum salmon," added Krkosek. "The juveniles are so vulnerable because they are so small -- only one to two inches long."

Dr Mark Lewis, a mathematician and biologist at the University of Alberta who also worked on the project, added: "Only a small fraction of juvenile salmon survive to return as adults. The fish-farm sea lice are reducing that fraction even more."

Concentrations of sea lice are 30,000 times higher around fish farms in coastal waters than in deep waters.

Global consequences

The study's implications could be severe for wild salmon. Although the study was conducted in B.C., researchers say the results apply globally.

Dr. John Volpe, a University of Victoria biologist and study co-author, said even the best-case scenario of an additional 10 per cent mortality rate for wild salmon from sea lice could push a fish stock "into the red zone."

The study also raises the question of "whether we can have native salmon and large scale aquaculture -- as it is currently practiced -- in the same place," added Dr. Ransom Myers, a fisheries biologist at Dalhousie University.

Salmon farms in Canada are found in B.C., New Brunswick and Nova Scotia. The industry is generally run by a few multinational corporations that operate in, aside from Canada, the U.S., Scotland, Ireland, Norway, Chile and New Zealand.

The report is the latest controversy to hit salmon farming.

In June 2005, Canadian Food Inspection Agency scientists found the presence of the cancer-causing chemical malachite green on two Vancouver Island salmon farms.

Two years ago, scientists warned that some farmed salmon contained potentially harmful levels of cancer-causing toxins and that consumers should consider restricting the amount they eat.

Wild Atlantic salmon populations have drastically declined over the past 30 years in North America.

While there are many factors involved, scientists and conservation groups believe some aspects of aquaculture have contributed to the decline.

In March 2005, Krkosek, Lewis and Volpe were part of a study that found parasitic sea lice from fish farms also endanger other important ocean species such as herring.

Citing concerns over declining populations of native juvenile salmon off northern Vancouver Island, the government announced plans last year to do more research on the matter.