Who’s Been Naughty?

mauve stinger

Salmon slayer a.k.a. mauve stinger. Photo credit: Reuters

Last week, the mauve stinger, Pelagia noctiluca, which has terrorized beaches in the Mediterranean for years, swarmed into a salmon farm, Loch Duart, off the Scottish coast. The berry-sized jellies slipped through the nets that hold the salmon and lodged themselves in the gills of the fish.

Loch Duart is located on one of the oldest aquaculture sites in Scotland, and it’s committed to sustainable farming. It has nine sites, but only farms six at a time. The other three remain fallow, a practice also encouraged by sustainable land-based farming. On land, fallowing gives the environment a chance to return to its natural condition, and in the sea it does too.

Importantly, fallowing in the ocean cuts down on the populations of sea lice that infest salmon kept together in pens. These parasites latch on to the skin of the fish, opening them up to infection. Hoping to keep sea lice levels as low as possible, Loch Duart has also been testing how cleaner wrasses that naturally snack on sea lice can help control the parasite. And instead of using toxic anti-fouling chemicals, Loch Duart cleans their nets by hanging them in the air. Drying kills nuisance algae and shellfish–as well as jellyfish polyps–that cliScreen Shot 2014-12-24 at 11.49.27 AMng to the nets.

The reputation of the company’s environmentally friendly practices, not to mention their tasty fish, has become well-known. Loch Duart salmon was served at William and Kate’s wedding and at the Queen’s jubilee.

The company’s managing director, Nick Joy, whose name does happen to have a holiday ring, visited the farm just after the recent jelly infestation. “My immediate view was that though the fish had been sorely tried, the majority of them would survive as long as the weather gave them some peace to rest.”

But it didn’t. A gale came up that trapped some of the fish who were already suffering. Three hundred thousand died.

This isn’t the first time jellyfish have been naughty to salmon farms. In 2007, the mauve stinger turned a quarter of a million salmon at the Northern Salmon Co. in northern Ireland into corpses almost overnight. The loss was estimated to be half a million dollars. In October 2013, up to 20,000 salmon farmed by aquaculture company Marine Harvest were slain during a jellyfish bloom off Clare Island in Ireland. A report from Scotland and the Orkney Islands revealed that of the 4.7 million fish lost from fish farms between 1999 and 2005, jellyfish accounted for 60%.

Nick Joy said, “This sort of issue represents the challenge of farming in a wild environment.  Agriculture has been around for a long time and has worked out how to deal with most of the major challenges that face it. Aquaculture is new. Salmon farming is approaching its 50th birthday and we have learnt much but each year brings a new challenge and some new lessons.”

Because the company was already pulling in strong numbers and good harvests for 2014, it will survive. But there’s no denying this jellyfish attack was a big lump of coal.

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