Lepeophtheirus salmonis, or the common salmon louse, now infests nearly half of Scotland’s salmon farms. Last year lice killed thousands of tonnes of farmed fish, caused skin lesions and secondary infections in millions more, and cost the Scottish industry alone around £300m in trying to control them. Scotland has some of the worst lice infestations in the world, and last year saw production fall for the first time in years. But in the past few weeks it has become clear that the lice problem is growing worldwide and is far more resistant than the industry thought. Norway produced 60,000 tonnes less than expected last yearbecause of lice, and Canada and a dozen other countries were all hit badly. Together, it is estimated that companies across the world must spend more than £1bn a year on trying to eradicate lice, and the viruses and diseases they bring. As a result of the lice infestations, the global price of salmon has soared, and world production fallen. Earlier this year freedom of information [FoI] requests of the Scottish government showed that 45 lochs had been badly polluted by the antibiotics and pesticides used to control lice – and that more and more toxic chemicals were being used.
“Sea lice are a natural phenomenon,” says Scott Landsburgh, chief executive of the Scottish salmon producers association. “All livestock on farms, terrestrial or marine, are encountering some kind of parasite or tick, and they’re dealt with. And that’s part of livestock farming. We are no different to terrestrial farms. Problems come and go, depending on biology and the environment. The louse is a hardy parasite. It’s a challenge for Chile and Norway, too. We are spending a lot on all sorts of things.”The salmon-farming industry, which has grown at breakneck speed since the 1970s, knows it has a huge problem, but insists it sees the lice as unwelcome guests that will soon be evicted rather than permanent residents. Rather than dwell on the lice, industry leaders point to the fact that in just 40 years, aquaculture has gone from providing 5% of the world’s fish to nearly 50%, and in Scotland, from a few hundred tonnes of salmon a year to more than 177,000 tonnes in 2015. They argue that new methods to control infestations are being developed and the chemicals being used are safe and degrade quickly, adding that they expect to have found a solution within a few years.
The global companies that dominate ownership of the farms, buoyed by high prices and growing worldwide demand, are confident that they will find solutions. Marine Harvest, the giant Norwegian multinational that grows 40,000 tonnes of salmon in its many Scottish farms, said this week that it needs to develop more effective ways to combat lice. The use of the toxic drug emamectin rising fast, but also that the industry had persuaded the Scottish environmental protection agency to withdraw a ban planned for next year. Other papers showed that the levels of chemicals used to kill sea lice have breached environmental safety limits more than 100 times in the last 10 years. The chemicals have been discharged into the waters by 70 fish farms run by seven companies.
FoI documents show that the Scottish industry wants to “innovate” by building the world’s biggest salmon farm, which would triple the size of the largest now in operation. It could farm 2m fish at a time, and create as much waste as a city the size of Glasgow. The anwwer to the inevitable lice problems, say environmentalists, is to move the farms further offshore into deeper, colder waters, where lice are less able to survive, or to even put them on land, where they could be better controlled. But this would add greatly to industry costs and require investments of billions of pounds. In the meantime, the companies are using mechanical ways to trim the lice from the fish. These range from pumping the fish through water hot enough to make the lice let go of their hosts, to churning them as if in a washing machine. Both are condemned by animal welfare group Compassion in World Farming, and are known to be expensive and not always effective. Last year the heating of the water on a Skye fish farm led to the accidental slaughter of 95,000 fish. Another 20,000 died in another incident.