A breeding programme aimed at reversing declines of the white-clawed crayfish has produced 300 young this year in the Yorkshire Dales.
Natural England, the government’s conservation body, said the success of the breeding scheme offered a ray of hope to the rare native crustacean.
The white-clawed crayfish is one of England’s most threatened species.
Natural England and the Environment Agency are seeking funding to expand the programme, which began in 2003.
The white-clawed crayfish was once common in upland rivers and streams but is being driven out by its invasive cousin, the American signal crayfish.
The more aggressive American species, which was brought to the country to be farmed, also carries a “plague” which is fatal to the native crayfish.
The project began in 2003 by ring-fencing native crayfish to protect them from the plague and predation by the American species to an active breeding programme, and developing techniques for captive breeding and rearing of the white-clawed species.
Natural England said a stock assessment recently showed that more than 60% of hatchlings survived in the captive breeding programme.
It wants to expand the programme to produce at least 500 white-clawed crayfish a year, which would be released once they reached sexual maturity.
Dr Helen Phillips, chief executive of Natural England, said: “The news that white-clawed crayfish are breeding in increasing numbers in the Yorkshire Dales is extremely encouraging and shows that targeted conservation work can make a real impact.
“The species has been all but wiped out following the introduction of its American cousin, but the success of this project gives grounds for hoping that extinction is by no means inevitable.”