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| Salmon farms teeming with lice
threaten wild fish Tim Radford, science editor Wednesday March 30, 2005 The Guardian Canadian scientists have confirmed that salmon farms are a threat to wild salmon. Researchers monitored 5,500 baby salmon along a 37-mile long migration route past a fish farm, to find the juveniles exposed to 30,000 times the normal risk of parasitic infection. Sea lice are a hazard for all salmon. But freshly hatched salmon heading for the sea - no bigger than a little finger - are particularly at risk. If there are enough of the parasites, sea lice can quite literally eat their host alive.
"Our research shows that the impact of a single farm is far reaching," said Martin Krkosek of the University of Alberta. "Sea lice production from the farm we studied was four orders of magnitude, 30,000 times, higher than natural [levels]. "Infection of juvenile wild salmon was 73 times higher than ambient levels near the farm and exceeded ambient levels for 30km [19 miles] of the wild migration route." The team followed baby pink and chum salmon, 3cm long and some weighing only half a gram, on their journey to the sea. They caught them every one to two and a half miles, looked for parasites, and returned them to the water. The fish had to pass through a long, narrow fjord, packed with anchored cages of captive salmon. The team found almost no sea lice on the juveniles before the farm - but heavy infections as they approached it. The researchers then found a second danger. The outward bound school of wild juveniles became a moving cloud of contagion. Sea lice larvae matured on the young salmon, to produce up to 800 eggs each. "The lice will attack other species, not only salmon but other fish such as herring which are the spark plugs of entire ecosystems - everything depends on them, from salmon to seabirds to whales," said John Volpe of the University of Victoria, another of the team. "Every commercially important fish is either directly or indirectly dependent on herring." Aquaculture is the fastest growing sector of the food business. Farmed Scottish salmon now brings in £700m a year over shop counters. Salmon farming in Scotland is bigger than the Highland beef and lamb industries combined. Scottish salmon farmers have been under pressure from environmentalists. A study published in Science last year reported that Scottish farmed salmon had greater concentrations of toxic pollutants than wild salmon. But Mike Donaghy of WWF Scotland said that the Canadian research might not be relevant to Scotland, with a coastline managed in ways designed to reduce infection. "Norway has a fjord coastline, but we don't. We have a sea loch
coastline. It is further evidence that if you have big accumulations of
fishes, giving off lots of parasites, you are going to affect your wild
fish," he said. "And there is the key to the whole thing: how sustainable
are these fish farms, in comparison with a sustainable wild fishery?" |
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