Fisherman on England’s Northern coast have been finding a curious catch in their nets recently—Canadian lobster.

The Homarus Americanus is native to the Atlantic ocean, just off the North American coast—3,500 miles away from the U.K. Are the lobsters just taking a leisurely swim across the pond?

According to fishery experts, no. 

Researchers now believe passengers aboard Atlantic-crossing cruise ships have actually been buying live lobsters and, in a misguided effort of animal rights activism, throwing them overboard in an effort to save the crustaceans, reports the Daily Mail. Many of the lobsters caught still have the rubber bands around the their claws, according to local fishermen.

“In the past we have heard one officer on the watch talking to another on the cruise ship saying some of the passengers were going to buy lobsters and release them, thinking they were doing good,” Gary Redshaw, a skipper who has found the foreign lobster species in British waters, told the Yorkshire Post.

“But in fact they can do a lot of damage. I think it’s a good idea to study them as they could be giving English lobsters a disease.”

The North American lobsters are unable to breed with local lobster species and usually die quickly in the unfamiliar habitat. Experts also warn that the two new species could bring more harm to local lobster populations.

“They are usually Canadian lobster as they are cheap. But the chances of them being established are very rare,” Mike Cohen, Chief Executive of the Holderness Fishing Industry Group said. “They won’t last much longer than if the passengers had eaten them for dinner.”

Foreign “marine litter” was blamed for wiping out a native English oyster a few years ago.