Simple salmon

Scottish environmentalists oppose use of chemicals to control sea lice and favour organic salmon

Published: Friday 31 October 1997

a coalition of Scottish environmental groups under the banner of the Scottish Wildlife and Countryside Link (swcl) has called for a review of the environmental impacts of marine salmon fishing in Scotland. The main cause for concern is the wide and indiscriminate use of chemicals to control sea lice, parasites which attack farmed salmon. According to estimates, the cost of sea lice to the industry in terms of fish losses and treatment is close to 22 million ( us $ 35 million) per year ( Pesticides News , No 37, July-September, 1997).

The most commonly used chemical to control sea lice is organophosphate (op) dichlorvos, which was strongly opposed by environmentalists from the start. Organophosphates are persistent chemicals and pollute the water, affecting life forms other than those for which they are intended. But op dichlorvos was the only chemical licensed for sea lice treatment until hydrogen peroxide came into use in 1993. Another chemical, ivermectin, has been in illegal use in Scotland since 1991. The controversy rose afresh when use of the latter was allowed by the government in 1996. In the same year, use of another organophosphate, op azamethiphos, was granted by the government, and is freely sold in the market.

Further research to bring alternative treatments into the market has been undertaken by pharmaceutical companies, and a major research programme to develop a vaccine for sea lice was launched in the 1980s. But the swcl report, written by aquatic environmentalist Alison Ross has asked the industry to place more emphasis on prevention of sea lice and disease in salmon.

Recommending improved husbandry practices, especially with regard to stocking densities, the report says that the industry should adopt the use of biological controls such as the cleaner fish (small fish that live in symbiosis with larger fish by cleaning decaying matter and miniature organisms off their bodies) and develop non-chemical means. It asks the Scottish Environmental Protection Agency to promote use of such methods and urges it to adopt a clear stance against the use and development of toxic chemicals.

The first certificated organic salmon have recently been harvested off the western coast of Ireland. The fast flowing tides and exposed conditions near Clare Island ensured that there were very few lice and disease problems.

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