A report for Traffic, which monitors and seeks to uncover traders in endangered species, says lawlessness prevails along much of the shores of the Caspian Sea, stronghold of the sturgeon whose unfertilised eggs make caviar.
Quotas and fishing techniques used to conserve the fish, which can take up 25 years to mature, have largely disappeared.
According to official figures, the legitimate catch in the Caspian fell by three-quarters between 1984 and 1994. Yet, says the report published today, exports appeared to be unaffected while the amount of effort put into fishing increased. It concludes that at least 50 per cent of the catch is illegal.
Tom De Meulenaer, director of Traffic in Europe, said: "Immediate measures to seriously control the whole industry, from fisheries to the consumer, are required if the industry and sturgeon are to survive."
There are 25 species of sturgeon, two of which are believed to be particularly endangered. But 90 per cent of the world's catch and caviar comes from three species found in the Caspian Sea - the beluga, the Russian and the stellate. The Beluga can grow up to 20ft long. The main exporters are Russia and Iran and the biggest single importing bloc is the European Union. Britain takes about 30 tons of caviar a year, making it the continent's third biggest consumer after Germany and France. In Britain caviar can be bought only from up-market department stores and specialist outlets. A 30-gram jar costs about pounds 30.
The report puts the blame for poor fisheries control and smuggling on Russia and two of its neighbouring republics, Astrakhan and Azerbaijan. It says that some caviar coming into Europe has been suspiciously cheap, indicating that it has been smuggled or that its origins are illicit. But fishing is not alone in creating the plight of the sturgeon, which evolved 250 million years ago - before the dinosaurs. Damming of its spawning grounds, damage and diversion of waterways and pollution have added to the threats. Tumours and other disorders have been found in adult fish, while analysis of caviar samples on sale in Britain revealed very low traces of toxic organo- chlorine compounds such as DDT and PCB.
But fishing is by far the main culprit and the report, endorsed by the World Wide Fund for Nature, calls for the rapid restoration of proper controls on the fishery.
The report says trawling for sturgeon, once outlawed as a conservation measure, has resumed. The illegal fishing is no secret - in 1994 Russian authorities said they had detained more than 1,000 poachers, confiscated more than 100 tons of sturgeon and five tons of caviar, and shut seven illegal caviar processing plants. Only one species of sturgeon, the common, occasionally visits the seas around Britain. A few are caught off our coast each year.
t John Gummer, Secretary of State for the Environment, flew to Argentina last night for international treaty negotiations on conserving wildlife. However the Government was under fire for neglecting endangered sea birds on the mid-Atlantic island of Ascension. A plague of feral rats and cats, introduced by man, has severely depleted their numbers.
Experts have devised a pounds 1.5m plan for eradicating the pests, which eat eggs and nestlings on the UK dependent territory. But the Government has only offered to cover 2 per cent of the cost.
A spokesman for UK conservation charities, including the Royal Society for the Protection of Birds, said they were happy to pay a large share but ``the bottom line is that we expect a serious contribution from the Government''.