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A Lion's Mane jellyfish in Dublin Bay. Sasko Lazarov/Photocall Ireland
from the deeps

Lion's Mane jellyfish spotted on Irish beaches as annual numbers rise

A sting from the Lion’s Mane jellyfish can cause nausea, sweating, cramps and headaches.

AN ABUNDANCE OF Lion’s Mane jellyfish have been reported at beaches around the country over the last week, particularly along the east coast.

The Lion’s Mane jellyfish, which can reach a diameter of up to two metres, has increased in number along the Irish coast over the last several years.

The presence of the jellyfish on Irish beaches is “getting worse” every year, according to the CEO of Water Safety Ireland John Leech. 

Speaking to he said that there is “no question about it that there are more Lion’s Mane jellyfish every year”.

“20 years ago, you hardly ever heard of one. You’d get the barrel jellyfish which is a big jellyfish but it’s not as big as the Lion’s Mane,” Leech said.

“The biggest infestation that we seem to get is between Wales and Dublin, North County Dublin and as far as Louth, that’s where the greatest numbers of them seem to be,” he said.

Leech said that there have been more sporadic sightings of the jellyfish on the south, west, and north coasts.

“There were a few in Galway last week, and down in West Cork and Kerry, but in much, much smaller numbers [than the east]- the big problem is with the Irish Sea this year.”

The Lion’s Mane jellyfish prefers the cooler water of the Irish Sea and particularly the waters off the coast of Dublin.

Its tentacles give a painful sting that can cause nausea, sweating, cramps, headaches and other symptoms.

The public is advised to seek medical attention for any serious symptoms.

Leech said that in Fingal in north Dublin it would be usual to receive reports of the jellyfish around this time of year, but not the extent witnessed recently.

“All jellyfish over the last twenty years, and even more now in the last five years, have been increasing steadily,” said Leech.

 “The reason, we believe, is due to overfishing. If you don’t have fish predating on the jellyfish, and the column of water is clear for them, of course, they’re going to breed.”

“Turtles love eating Lion’s Mane jellyfish, but the number of turtles has gone down.

It’s a combination of fewer turtles and overfishing of those that predate on the jellyfish.

Leech said that the public should exercise caution when entering the water, particularly at beaches which do not have a lifeguard.

Fingal County Council has advised that conditions for the jellyfish are ideal from the middle of August until the second week of September, leading to a “noticeable increase” in their numbers on beaches and in the water.

The Council is urging swimmers to exercise vigilance on beaches where Lion’s Mane jellyfish have been spotted.

“Please note that even when they’re dead and washed up on the beach, the venom stays in their tentacles for a few days,” the Council advised.

With so many long trailing tentacles there is a chance you could still get stung, even when you try not to swim near them. Also, fragments of the lion’s mane jellyfish tentacles that break off in the water will sting you, even if they’re no longer attached to the jellyfish.

A spokesperson for Wexford County Council said that the Lion’s Mane jellyfish has been reported on beaches in Wexford, including Duncannon beach.

“We have cautioned people to be vigilant and to be careful,” a spokesperson for the Council said.

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