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Ocean warming blamed for deadly stingers' migration north from their Mediterranean home

by Craig Weatherby

Until 10 years ago, the medusa jellyfish was known primarily as a colorful pest that afflicts bathers in warm Mediterranean waters.

They began appearing in the ocean off Britain and Ireland in the late 1990's, albeit uncommonly.

Last week, these minor, anomalous incursions turned into a swift, massive, and deadly invasion.

Billions of medusa jellyfish swarmed fish pens at a salmon farm anchored about a mile offshore in Northern Ireland's Glenarm Bay and Red Bay, north of Belfast on the eastern coast

The jellyfish formed a dense pack about 10 square miles and 35 feet deep.

According to John Russell, managing director of The Northern Salmon Co. Ltd., workers tried to rescue the salmon, but their boats couldn't get through the thick mass of jellyfish in time.

When the boats finally pushed through to the pens, all of the farm's approximate 120,000 fishworth about $2.1 millionwere dead or dying from stings and stress.

Russell said he had never seen anything like it in his 30 years in the salmon farming sector.

As he told the Associated Press, “It was unprecedented, absolutely amazing. The sea was red with these jellyfish and there was nothing we could do about it, absolutely nothing” (Pogatchnik S 2007).

All the company could do was collect and incinerate the mountains of stinking, dead salmon.

Mediterranean jellyfish had never previously been reported in Northern Ireland, but smaller swarms have occurred in western Scotland, western Ireland and even further north than the Glenarm Bay salmon farm, in Scotland's Western Isles (Outer Hebrides).

Global warming cited as likely factor

The species of jellyfish that attacked the farmthe medusa (Pelagia nocticula) or mauve stingeris famous for the purple glow it displays after dark, and its habit of plaguing swimmers in the Mediterranean Sea.

Scientists cite this subtropical species' increasing appearances in UK waters as evidence that global warming is raising ocean temperatures.

Ocean warming can create unusual currents that carry subtropical species well north of their normal stomping grounds: a phenomenon increasingly witnessed around the world.


  • McKee L. Blown in: Mauve Stinger jellyfish attacked the Glenarm salmon. Accessed online November 21, 2007 at
  • Peck S. Jellyfish attack wipes out salmon farm. Accessed online November 21, 2007 at
  • Pogatchnik S. Jellyfish Kill 100K Salmon in N.Ireland. Accessed online November 21, 2007 at


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