TOXIC chemicals used by salmon farms could be killing off tiny animals that are vital to the marine food chain, scientists warn in a confidential report for the British government leaked to New Scientist.
Salmon farming is one of the world's fastest growing food production industries. For the first time, the total amount of Atlantic salmon reared in cages in Norway, Chile, Scotland, Canada and elsewhere is expected to top one million tonnes this year. But as the industry has grown, so have concerns about the pollution, disease and genetic contamination it may spread. Now, evidence from one of the biggest scientific investigations to date suggests that the pesticides applied at hundreds of salmon farms may be harming the marine environment. The fish are fed or bathed in cypermethrin, azamethiphos or teflubenzuron to kill the sea lice that plague them. The lice damage the health of the fish, and in turn the salmon farming business. But shellfish farmers and environmentalists have long suspected that the chemicals could be harming other marine wildlife.
These fears prompted the British government to launch a (GBP)750,000 study in 1999, involving regulatory agencies, marine laboratories and the salmon farming industry. New Scientist has seen the 178-page second annual progress report of this study, dated April 2001. The report includes the interim results of a study by the Plymouth Marine Laboratory, which surveyed small invertebrates around salmon farms in Loch Sunart and Loch Craignish on the west coast of Scotland. The researchers found a drop in the number of nematode worms in the sediment close to the fish farms. They were also worried about "the almost complete absence" of copepods, tiny crustaceans that are an important source of food for young fish. Although this could be partly explained by poor sampling, they believe it "suggests the possibility of a large-scale effect that may be related to the use of chemicals on the fish farms". Lab experiments at the Dunstaffnage Marine Laboratory near Oban back this up. They show that the chemicals either kill or deform copepods at concentrations as low as 100 nanograms a litre. So far, however, the Dunstaffnage researchers have not been able to find the effect in the wild. In the past, the research effort was hampered by a lack of cooperation from fish farmers. Dunstaffnage's project leader, Kenny Black, described this as "very frustrating" in the leaked report. Now, though, relations are said to be much improved. The salmon industry's critics have seized upon the new findings. Friends of the Earth Scotland says they suggest that salmon farming is having a much wider impact than previously realised. "This report reveals that salmon farming is a very dirty business," adds Alan Berry, a former shellfish farmer who voiced some of the original fears. But Dunstaffnage's director, Graham Shimmield, stresses that the research is still in progress.
"Laboratory experiments so far suggest that fish-farm chemicals may have an effect," he says. "The challenge now is to quantify that effect." He cautions that the impact on marine wildlife may not be as large as many critics suggest.:
