My plan to present a series of articles giving the story of the expansion of fish farming in Scotland in some sort of logical order is being derailed by current events. Most recent is the publication, by the charity WildFish, of a devastating set of data on the impact of sea lice on our wild salmon and sea trout. The report details an industry that allows farms to emit up to five million sea lice at a single time (with one farm having emitted two billion in just one week) and 40% of emissions reported by the industry to regulators being in excess of the industry’s own Code of Good Practice.
Many companies simply fail to report on sea lice figures, presumably when doing so would result in action by SEPA. Better to face a warning message (nobody ever gets fined) than force a shut down. The report can be accessed here and it was followed by a devastating article by Vicky Allan in The Herald.
Sea lice – an introduction
Sadly, we have reached a stage where our most successful aquaculture product is a sea louse. It’s just a great pity that we don’t have any innovative cooks presenting recipes for dishes such as sea lice risotto.
Rather than repeating what can be read via the links above, I will instead present a brief introduction to the sea louse. It is best seen as the smallest member of the crustacean family, with much larger and tastier cousins including lobsters and crabs. This simple fact has bedevilled the industry from its earliest days, because the pesticides that have been used to eliminate sea lice are also deadly to their more valuable relatives, on which our traditional West Coast creeling industry depends.
In this regard, large, foreign-owned aquaculture companies displacing locally-owned small businesses mirrors classic examples in nature, such as the arrival of grey squirrels triggering the decline of red ones. But let’s not get anthropomorphic, let’s look at the science.
Sea lice start out as plumes of eggs released from a mature female in their thousands into the tidal stream. They have no ability to swim and are just carried along the coast in the tidal streams until they find a host fish, at which point they use their tiny pincers to attach themselves. They then mature, growing legs that enable them to move about and literally eat the host salmon or sea trout alive.
Sea lice do, of course, exist in a natural environment, but the problem for the industry, and those who try to regulate it on our behalf, is that by caging unnaturally large populations of salmon, a perfect breeding ground is created. Placing those cages in inshore waters, near to the rivers that have traditionally been home to wild salmon and salmonids, has created a disaster for the latter. The wild smolts that emerge from their native rivers can be as small as 10 cm in length and 10 grams in weight.
They will inevitably find themselves swimming through clouds of immature sea lice and just a couple of hits can prove fatal. It’s interesting that some fish farm companies are now growing smolts to weights of up to 90 grams in fresh water lochans before putting them out to the cages, to give them a better chance when the sea lice attach themselves.
Pesticides and problems
The reaction of the industry has been to put powerful poisons, such as Emamectin Benzoate (EmBz), marketed as SLICE, into the salmon’s feed. It passes through the fish and research commissioned by SEPA has proved beyond doubt that it stays active on the seabed for periods of up to four years, where it will be fatal to wild crustaceans, especially in their juvenile stages. By the way, that research was delayed for years, when the makers of SLICE threatened SEPA with legal action, so it has been extremely well peer-reviewed!
The sea lice reacted naturally to the widespread use of EmBz by developing an immunity to it. In a talk in 2013, sadly no longer available online, Dr Mark Fast of the University of Prince Edward Island said:
“1999 was the year the aquaculture industry gained what would be its most powerful tool in the fight against sea lice. It’s called SLICE…. It’s an in-feed treatment that, for a time, acted like a silver bullet. It was so effective that as a researcher studying sea lice, I found it difficult to harvest sea lice from salmon in an aquaculture environment. I just couldn’t find them. It worked that well….SLICE’s effectiveness started to seriously wane around 2008. The sea lice were adapting. The previous two summers had been worse than ever. Sea lice were partying even harder than they were in 1999.”
Dosages of EmBz were steadily increased, but given that its use will almost certainly soon be disallowed, the industry has reacted in different ways. One has been to use hydrogen peroxide (basically bleach) which kills most things, but at least does not stay long on the seabed after use. More significant has been the use of ‘cleaner fish’, mainly wrasse and lumpsucker. These are the small, curious-looking scavengers that inhabit shallow coastal waters and act as miniature coastal cleaners, eating tiny crustaceans such as sea lice as they go.
The immediate effect of aquaculture companies deciding to put cleaner fish into the salmon cages was a massive hike in their prices, literally from zero, as they had never been perceived to have any value until then. The public first learned of this when, for example, locals in Dorset found fleets of small inshore fishing boats hoovering up their local wrasse, disturbing the natural balance of the coast, with the inevitable result of some anti-Scottish hostility once the destination became known.
But what appeared to be a natural solution wasn’t all it seemed. Wrasse and lumpsucker have long and complicated lives, for example only breeding when mature. This made supply difficult, as they are required to be culled along with the salmon going to market, otherwise viruses can transfer to the new stock. Further, transparent mutations of sea lice are now appearing, invisible to the cleaner fish.
The result has been experiments in breeding cleaner fish, with our Scottish Government ever willing to help our Norwegian and Icelandic friends, putting a lot of money into research and development. We now have the spectacle of an industrial hatchery in a formerly lovely bay at Machrihanish, producing wrasse that will spend their lives in a cage eating sea lice, while they themselves are eaten by them, and end up as biowaste.
