TALES FROM THE RIVERBANK In spring 2012, Marine Harvest stocked one
million juvenile salmon smolts into its sea cages near Kinlochleven in Lochaber. As some- thing of an experiment at the time, but based on many years of quiet research, it also added 58,000 ballan wrasse. The results have taken even the most posi-
Wrasse rescue
Using ‘cleaner fish’ in salmon farms could help to stop sea lice problems for wild fish
WORDS JON GIBB B
eing an angling writer and living on the West Coast of Scotland, it’s all too easy to become a bit of a single issue obsessive.
Because in some ways there has only really been one story for the salmon and sea trout of the Western Highlands in the past three decades, and that’s the devastation wreaked by the rapidly expanding salmon farming industry. So it’s rather nice, just for a change, to be
able to report a genuinely positive development affecting caged salmon and their wild counter- parts; something that truly has the potential to solve a seemingly intractable problem. Science now tells us that infestation by para-
sitic sea lice from fish farms has been the main cause for the free-fall in West Coast sea trout numbers since the birth of the industry in the 1980s. The evidence for impacts on wild salmon is less robust, but deep suspicions remain. Sea lice are also the main health problem for the fish farmers, with a reported £30-40 million spent each year by the sector in lice manage- ment measures and treatments. Over the past few years though, instead of
continuing with research into yet more novel chemical compounds to control this threat (the parasites have developed a resistance to every single one), the industry has been looking at more organic and sustainable options. In a major new development, farmers are
now stocking their cages with ballan wrasse, a fairly inconsequential little fish that lives along our rocky shorelines but, most importantly, has a voracious appetite for crustaceans. These ‘cleaner fish’ as they have become known look set to revolutionise the way in which the indus- try controls the threat of sea lice.
‘Early signs are that this is about the best piece of news for West Coast anglers since salmon farms first appeared’
tive within the company by surprise. It takes nearly two years to grow smolts to adult salmon in sea cages ready for the supermarket. Within that time there can be a need for near constant treatments to keep them clear of lice. The Loch Leven ‘class of 2012’ was recently harvested with the astounding news that it did not need one single chemical treatment throughout the whole cycle to keep it lice free. In fact at times the wrasse needed to be fed crushed mussels as they had done such a good job with any sea lice that had been attracted to the caged salmon. These ground-breaking results have filtered
throughout the Scottish industry, and now all of the major operators are using wrasse as part of their lice control strategies. The implications of this for wild fish conservation, if it can be replicated all over the West Coast, are nothing short of enormous. The wider economic impli- cations are even greater. Let’s not forget that the industry has a farm gate value of £600 million, employs nearly 6,000 remote rural workers and that farmed salmon ranks only second to whisky in terms of export value. Of course this new method of biological
control is not without its teething problems – not least the pressing need to farm the cleaner fish themselves – but of course one of its major advantages is that the critical issue of chemi- cal resistance is removed, something that only last year was presenting a possible nightmare scenario as there was nothing left in the fish farmers’ medicine cabinet that didn’t have resistance issues. Boosted by this early chemical-free success,
other more organic-style approaches are also being developed, including the similar use of lumpsuckers as cleaner fish, the discovery by Argyll-based company Landcatch of a lice resistant gene and, perhaps the Holy Grail of lice control, a race to find a sea lice vaccine. It would of course be premature to describe
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these cleaner fish as the silver bullet we in the angling community have all been waiting for – we do not for instance know yet whether our new fishy neighbours will bring some as yet unknown pathogen or disease, and we should also be wary if this signals any more salmon farm development near the mouths of salmon rivers. But early signs are that this is about the best piece of news for West Coast anglers and conservationists since the first salmon farms appeared in our estuaries all those years ago.
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