However, John Russell, from Northern Salmon Co Limited in Glenarm, said plans were in place in efforts to ward off the jellyfish should they attack stock.

A number of suspected mauve stinger jellyfish had been spotted on Sunday on Portrush’s West Strand by a Northern Ireland Environment Agency staff member when he was out walking with his family.

Samples of the small purple jellyfish were collected and stored overnight in an aquarium at NIEA’s coastal zone before being sent to a laboratory at Queen’s University, Belfast which confirmed the jellyfish were the species known as Pelagia noctiluca, or mauve stinger.

Northern Salmon – who lost more than £1 million worth of stock when the deadly jellyfish descended on them last November – were immediately contacted by the NIEA, who also discovered that the jellyfish were also present at Portrush and the White Rocks, as well as having been observed in the Republic, off the Co Sligo coast.

Manager of Northern Salmon Co Limited John Russell explained that they had a mitigation system in place that was not 100 per cent effective, but should go some way to helping ward off a situation similar to the one last year.

Columns of bubbles using compressed air are used to try and force the jellyfish out from the nets containing the salmon if they should try to come in and attack the stock.

“We will also be using tarpaulin curtains around the nets to try and stop these beasties from getting in,” he said.

He said the company has had the system in operation since last year, although it was one widely used in agriculture for 10 years.

He told the News Letter that the level of its success would depend on the severity of the situation involving the jellyfish.

“We could be overwhelmed again, and if mother nature wants this (targeting the salmon again) then that is what she will do,” said Mr Russell, who admitted he was “very, very concerned” about a repeat of the 2007 scenario.

“We can only do what we can do, and hope that the jellyfish will not come near us.

“If the wind turns north-easterly we could be in trouble.”

He added: “We are hoping and praying that they don’t come near us.”

Meanwhile, the Northern Ireland Environment Agency is working in partnership with the Department of Agriculture and Queen’s University Belfast who are to “monitor the situation” regarding the appearance of the jellyfish over the next few days.

Gary Burrows, the NIEA employee who discovered the species at Portrush, said the agency was also offering support to QUB-based marine biologist Dr John Houghton, who has undertaken research into the species.

“We have also made contact with all the local coastal councils and National Trust properties, and advised them of the issue, and made them aware of the jellyfish,” he told the News Letter.

Gary also said members of the public were advised to treat any jellyfish stings with vinegar and not water.