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Chesapeake Blue Crab Spotted Along Ireland Shore. How Local Experts Believe It Got There

BALTIMORE (WJZ) -- A Chesapeake blue crab was recently spotted on the shores of Ireland. Now Irish officials are trying to figure out how it got there.

The National Biodiversity Data Centre in Waterford is trying to determine if it was a one-off occurrence or if there are more out there. Blue crabs are invasive to Ireland.

Local experts agree that the blue crab likely did not swim across the Atlantic.

Genine McClair, the Blue Crab Program Manager with Maryland's Department of Natural Resources, said blue crabs wouldn't travel that far.

"It's highly unlikely," McClair said. "Blue crabs, especially once they're mature, they tend to stay in the estuaries on the shelf, kind of closer to shore. They're not going to like move out far into the heart of the ocean. They're definitely not going to be able to cross all the way across and have like a food source the whole time."

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A catch of blue crab is seen on August 30, 2018 on a boat off the Tunisian coastal city of Zarzis. - Tunisian fishermen saw the blue crab wreak such havoc on their catches when it first appeared that they nicknamed it after the terrifying jihadists of the Islamic State group. But now -- four years after these scourges of the sea invaded their waters -- the predators have turned into prey as fishermen in the North African country cash in on the crustaceans. (Photo by FATHI NASRI / AFP) (Photo credit should read FATHI NASRI/AFP via Getty Images)

Allison Colden, a fisheries scientist with the Chesapeake Bay Foundation, agreed that it's unlikely the crab swam itself over to Ireland.

Instead Colden said it could have been transported there by a boat through its ballast water.

"Large ocean going ships have to take on a significant amount of water as ballast when they unload so that they can remain stable as they make these long ocean crossings," she said. "So that is one of the main ways that species are introduced in new places."

Experts say it's more likely the blue crab made its way over from the Mediterranean. Some blue crabs were introduced there decades ago and McClair said because of that they have encountered blue crabs in the Bay of Biscay.

Colden said it could also be a part of the seafood trade over there or an aquarium release.

According to the Irish Times, officials believe the crab may have been released into the wild.

"That's surprisingly more common than some people realize, especially sometimes these aquarium introductions," Colden said.

She said in the Potomac River, there are large goldfish, that were released by pet owners that didn't have the heart to flush them down the toilet.

"They become these huge, monstrous things," Colden said. She added there's been some invasive algae introduced that way.

Recently, the Chesapeake Bay Foundation shared a warning that from the US Fisheries and Wildlife that said zebra mussels were found on moss balls people use as filters in their aquariums.

They are asking people to bag them up and dispose of them because it's possible those highly invasive zebra mussels could get into waterways.

Young waterman pulls in crab trap from Chesapeake Bay as the sun rises in background, Dundalk, Maryland. (Photo by: Edwin Remsberg/VW PICS/UIG via Getty Image)

Although blue crabs are a beloved creature here in Maryland, they are a danger to local Irish species because they've been known to eat smaller crabs and they even have eaten other blue crabs, Colden said.

Blue catfish and northern snakeheads are among the invasive species found here in the Chesapeake Bay. Maryland officials want you to catch and kill them if you see them in our waterways.

Blue crabs are normally found in warmer waters like in the Chesapeake Bay and as far as the Gulf of Mexico. They normally mate from May through October. After they mate, the females move to saltier waters where they develop an external egg mass.

According to the Chesapeake Bay Program, each bright orange egg mass may contain between 750,000 and two million eggs.

The blue crab found in Ireland was photographed along the Dollymount Strand. Another report of a blue crab claw was also reported to the centre earlier this month. Irish officials are asking locals there to report sightings on the centre's website.

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This story was initially published on March 18, 2021. 

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