The population has plummeted from more than a million at the start of the 20th century to about 100,000 as a result of commercial hunting, degradation of the seal's habitat in the Caspian Sea, pollution, disease and drowning in fishing nets.

Researchers from the University of Leeds said recent surveys showed that in 2006 there were just 17,000 breeding females - barely enough to maintain a viable population.

A 2008 survey by the Leeds University team found the number of pups being born had plummeted by 60% from 2005 levels to between just 6,000 and 7,000 youngsters.

The collapse in numbers of the seal has led to it being moved from the "vulnerable" category in the IUCN's red list of threatened species to the higher concern category of "endangered".

Dr Simon Goodman, of Leeds' Faculty of Biological Sciences, said: "Each female has just one pup a year, so with numbers at such low levels, every fertile female that dies is a nail in the coffin of the species.

"We're hoping that the seal's change in red list status will help raise awareness about their plight and the many important conservation issues facing the whole Caspian ecosystem."

The team is drawing up a conservation action plan, which they said would require a ban on hunting as the first step to reversing the declines.

"Without a suite of conservation measures there is a very high risk the species will become extinct, and possibly within our lifetime," Dr Goodman warned.