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Ecology and salmon related articles

Parasites from Commercial Farms Could Threaten Wild Salmon

by Elizabeth Weise
USA Today, March 30, 2005

Salmon farming has proliferated in response to consumer demand for relatively inexpensive, always-available supplies of the popular dinner entree.

But a new study suggests that populations of wild salmon could be paying the price.

Researchers in Canada have found that wild baby salmon called smolts that pass commercial salmon farms on their way to the ocean are being infected with sea lice at rates 73 times higher than normal.

Sea lice are parasites that feed off the skin, blood and flesh of salmon. In salmon farms, where pens can hold tens of thousands of fish, antibiotics combat the pests.

Sea lice on the smolts, which are about the size of a triple-A battery, can kill the fish at that vulnerable stage in their development.

That means that increased infestation rates pose a threat to already declining wild salmon, says lead author Martin Krko{scaron}ek of the University of Alberta. The study was published in Wednesday's Proceedings of the Royal Society in London.

The number of sea lice on the smolts was sampled every mile or two along their 60-mile migration route from sites in British Columbia to the ocean.

Along the way, the smolts pass large salmon farms.

"We see them before they get to the farm with no lice, and then we see them being colonized with lice at the farm," Krko{scaron}ek says.

Andrew Dobson, a professor of the ecology of infectious disease at Princeton University who was not associated with the research, praised the study as one of the best of its kind.

Sea lice occur naturally, and all salmon populations are affected by them. But in general, Krkosek says, smolts have a few months to grow and gain strength before they become infected.

Chile, Scotland, Norway and Canada practice salmon aquaculture on a large scale. Krkosek says "there's a scientific paper trail" indicating that worldwide, such farms are associated with increased sea lice infections and declines in adjacent wild populations.

Salmon farmers disagree. "I haven't seen any evidence that high instances of sea lice around our farms are causing problems in terms of wild salmon," says David Rideout, executive director of the Canadian Aquaculture Industry Alliance in Ottawa. "The science has not shown that that's the case."

Says John Volpe, a co-author of the study from the University of Victoria: "The take-home message here is that when the consumer expects salmon to be available year-round for $2.50 a pound, you run into trouble."

Moving salmon farms to inland ponds or into closed systems in the ocean would take care of the problem and raise the per-fish costs only slightly, he says.

Elizabeth Weise
Parasites from Commercial Farms Could Threaten Wild Salmon
USA Today, March 30, 2005

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