Three fishermen have been fined for trying to smuggle a large catch of crayfish from Hampstead Heath in the first case of its kind.

In a landmark hearing, Heath bosses prosecuted three men who were caught red-handed with two carrier bags full of the red swamp crayfish, bagged in a midnight raid on the ponds.

The lobster-like creatures, which are not native Heath dwellers, have bred at an alarming rate and are now thought to number more than 5,000.

However, removing or harming the crayfish, which have been blamed for biting swimmers in the ponds, is a breach of Heath byelaws.

It is believed incidents of people stealing crayfish from the Heath’s waters are becoming more common but the City of London Corporation, which manages the open space, said this was an isolated incident.

Julian Glowacki, 27, who was fined �220 for breaching the by-law, told the Ham&High that he had not planned to sell his catch.

“My cousin wanted to put them in an aquarium,” said Glowacki, of Tollgate Gardens, in Kilburn Park. “It’s the first and last time I’ll do that.”

Highbury Corner Magistrates’ Court heard that on June 18, officers from the Heath Constabulary spotted the three men with their lines out on Hampstead number two pond – a designated fishing site. When questioned, the three admitted they did not have licences to fish. They were issued with a warning and told to move on.

But just after midnight the three were spotted again at nearby Hampstead number one pond, armed with a large fishing net.

Lawyer Philip Saunders, acting on behalf of the City of London Corporation, said the men were found with a large carrier bag of the pond life, with other crayfish crawling around their feet.

All three men were cautioned and when officers searched their car they found a second bag, teeming with more of the crustaceans.

Mr Saunders, who admitted this was a “fairly unusual case”, said: “When the officers returned them (crayfish) to the water they noticed that some had perished.”

The by-law states: “No person shall in any open space wilfully disturb any animal grazing or shall harry, ill-treat, or injure or destroy any animal, bird or fish, or take or attempt to take any animal, bird, fish or egg or set any trap.”

Riko Glowacki, 19, of Lopen Road, Upper Edmonton, and Wladislaw Grabowski, of Saint Dunstan’s Gardens in Ealing, were each fined �285 on Thursday of last week for breaching the byelaw.

A spokesman for the City said two students had been granted licences to catch the crayfish for research purposes, but it did not issue licences for people to fish the crayfish commercially.