Aquaculture off the Northern Irish coast has been devastated by a swarm of jellyfish that left 100,000 salmon dead. Stock worth £1million were suffocated in their cages by the swarm, which is estimated to have covered 25 square kilometres of sea and been up to 10 metres thick (Reuters, BBC, Guardian, AP). Some reports say there may have been billions of the mauve stinger jellyfish.

“In 30 years, I’ve never seen anything like it. It was unprecedented, absolutely amazing. The sea was red with these jelly fish and there was nothing we could do about, it, absolutely nothing.” says Northern Salmon Company managing director, John Russell (Telegraph).

The sea was so thick with jellyfish that workers could not even reach the cages. This type of jellyfish is not normally found in UK waters so the swarm could be evidence of global warming, according to some of the news reports. However Reuters quotes Russell as saying that such jellyfish blooms do occur every 10 or so years, and that last week’s could have been down to higher-than-normal water temperatures.

“It’s an unusual natural phenomenon which is unprecedented in Northern Ireland. One of the difficulties with the Glenarm site is the strength of the tide. The tide pulled in the jellyfish and the water cannot move through the cages. The fish have been stung and asphyxiated, because they have no water moving through the cages to bring oxygen,” says Mark McCaughan, the Chief Fisheries Officer with the Department of Agriculture (Belfast Telegraph).

Jellyfish killing salmon trapped in farm cages is also relatively common. In 2003 the Salmon Farm Protest Group released figures claiming that in Scotland 4.4 million fish died between 1999 and 2002, with 45% of deaths caused by jellyfish. Data from the Scottish Executive in 2002 puts the number even higher: “in recent years over 3 million farmed Atlantic salmon have been killed as a result of these blooms”. The executive is even working on a early warning system for fish farms (PDF).

UPDATE

Now they’re troubling Scotland (Reuters, The Scotsman).

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