A second pack comprising millions of juvenile mauve stinger jellyfish has been spotted off the coast of Scotland, less than a week after an overwhelming attack by Pelagia nocticula killed 100,000 salmon at a Northern Ireland fish farm.

The Marine Conservation Society (MCS) announced on Friday the sighting of massed mauve stingers and compass jellyfish (Chrysaora hysoscella). While the latter are "common in British waters during the summer", as Reuters explains, the former are rarely seen around the UK at any time of year.

The MCS attributed the cause of the mass migration to "wind and tidal factors", and asked fish farm owners and the public to keep a sharp eye out for these abnormal "blooms".

Saunders concluded: "Jellyfish swarms can impact on fish and shellfish farms, and while the conditions causing these current events remain unclear, such swarms may become more prevalent in Scottish waters as a result of climate change."

The mauve stinger is already well-known down in the Med, and has in recent years increasingly forced holidaymakers out of the water and back onto terra firma. The apparent increase in its numbers has been attributed both to global warming - which means the creature does not die off in the winter but breeds all year round - and "decimation" of its natural predators such as loggerhead turtles, sunfish, and trigger fish.

Marine scientist Ricardo Aguilar elaborated to New Scientist back in July: "But it's also just the general reduction in marine vertebrates [by overfishing]. Where vertebrates fall, invertebrates increase."

As NS summarises: "Small fish compete with the jellyfish for food, so fewer fish means less competition." In turn, the burgeoning jellyfish population then eats fish larvae, further threatening fish stocks. ®

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• Attack of the quarter-ton, 'fridge-sized' killer jellyfish (15 December 2008)
• Huge jellyfish pack slaughters 100,000 salmon (22 November 2007)
• Viral epidemic strikes Spain's Mediterranean dolphins (30 August 2007)
• Euro boffins warn of mass fish (etc) migration (5 March 2007)
• Jellyfish: nature's quickest on the draw (9 May 2006)