Two boys have sparked an alert for fishermen to keep an eye out for sturgeon after they are thought to have made one of the most unusual catches.
Fishermen along the English and Welsh coasts are being asked to watch out for sturgeon which is one of the most protected fish in the world, and the eggs of the beluga species are served as caviar.
The youngsters who sparked the alert were fishing at Hobbs, near Pembroke Dock in South Wales, when they hooked one about a metre long (3ft) last month.
"We are sure from the only photograph taken that it was a sturgeon and that it may be the forerunner of others arriving here. Where it came from is at present a mystery," said Steve Colclough, of the Institute of Fisheries Management (IFM).
The last of these fish reported in UK waters was nine years ago when one 2.6 metres long (8ft 6in) was caught in June 2004, also in South Wales, by a trawler 2.4 kilometres (1.5 miles) off Port Talbot.
Mr Colclough, chairman of the IFM marine section, said: "It is illegal to retain sturgeon and anybody catching one should return it quickly unharmed and alive to the water and then report it.
"Before putting it back they should note as many facts as possible - its length, overall condition, signs of damage or disease, the data on any tag attached to it and take a photo.
"A yellow tag would show the fish had probably migrated from the Gironde river in France where the European sturgeon is now being bred and released."
These fish would normally stay in the Gironde until they were about ten years old and they might then migrate to the open sea.
Mr Colclough added: "If they came to the UK they would most likely be caught in estuaries and still be juvenile fish. Normally they would live 50 or 60 years and grow up to three metres long (about 10ft)."
Anglers should report any sturgeon caught to their local Inshore Fisheries and Conservation Authority (IFCA) or to the Centre for Environment, Fisheries and Aquaculture Science (Cefas) on 01502 562 244 at Lowestoft, or 01305 206 600 at Weymouth.
Mr. Colclough would also like to hear from anyone who catches one on 01634 686460 or by e-mail to email@example.com.