When a 200ft-long Norwegian well boat pulled alongside a salmon farm and lowered its hoses into the sea on Tuesday, 16,000 adult fish began the final leg of a two-year journey, from egg to plate via an old commando base.
While wild Atlantic salmon brave predators, pests and fishermen when they swim thousand of miles at sea, the lives of their farmed cousins are similarly fraught with danger.
The fish in pens off the Isle of Muck, in the Inner Hebrides, had survived flesh-eating parasites, algae and amoebas that have caused production to fall for the first time in years.
By the time the adult fish were on board Ronja Challenger they had been doused in hydrogen peroxide and flushed through tanks of fresh water to treat amoebic gill disease. Their food had been spiked with a chemical known as Slice and they had been bathed in pesticide to rid them of sea lice, which can eat them alive. At a farm on Loch Leven, wrasse and lumpfish are put in the pens to eat lice off the salmon.
Marine Harvest, the biggest producer in Scotland, says that problems are being brought under control. “We have spent vast amounts of money,” Ben Hadfield, head of the Scottish business, said. “Now mortality is down, growth is up and we’re able to hold the fish longer to reach a higher harvest weight.”
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Scotland produces about 9 per cent of the world’s farmed salmon and is the third largest producer, after Norway and Chile, but the figures show that in 2015 production of Scottish salmon fell 4 per cent to 172,000 tonnes.
The fish on Muck had been stripped from their mothers’ bellies in Norway and shipped across the North Sea to an old commando base at Lochailort two-and-a-half years ago. They were reared in trays and then tanks, fed down a production line at about six months and vaccinated by machine.
They spent ten months in fresh water before they were pumped on board another well boat and delivered to Muck in March last year.
Mr Hadfield said that 18 months ago two of his farms on Lewis and Harris had lice levels of about eight to ten per fish and that they had to harvest the salmon at 3.5kg, a little over half their target weight. Last year across Scotland the average weight of fish fell from 5.6kg in 2014 to 5.2kg, because the longer they were left to grow at sea the more lice levels increased and other diseases inhibited growth. Mortality rates doubled from 7 per cent in 2014 to 14 per cent last year. According to Salmon & Trout Conservation UK about 20 million fish died on farms in 2015 and last year.
Mr Hadfield said that salmon farming was “coming through a very torrid time”. “Within the space of a couple of months we spent £12 million on hardware,” he said. That included three hydro-licers, which pump the fish out of pens and into fresh water, where lice cannot survive, then back into their sea pens. Mr Hadfield said that mortality was down to 3 per cent and production was up more than 30 per cent. “So far we have produced 36,000 tonnes this year, compared to 45,000 in the whole of 2016. We are expecting 59,000 tonnes this year,” he said.
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The fish on Muck, worth about £750,000 at wholesale prices, were pumped into two 90,000-litre tanks onboard Ronja Challenger and chilled as it sailed to the mainland.
Just after midnight they were pumped off at Mallaig and taken to a slaughterhouse, from where they went by road to a factory in Rosyth to be smoked, sliced and packed. The 16,000 fish will be in the shops next week.