CONSERVATIONISTS have called for urgent action to curb illegal fishing that is threatening to push the freshwater pearl mussel into extinction.

Buglife, the invertebrate conservation trust, and the Royal Society for the Protection of Birds (RSPB) say the mussel, which can live for more than 100 years, is one of the most endangered molluscs in the world, and that illegal poaching and pollution issues in Scotland threaten its future.

Up to half of the world's remaining population is believed to be found in Angus, the Cairngorms and the north-west of Scotland.

The International Union for the Conservation of Nature (IUCN) has warned EU member states need to step up efforts to prevent the extinction of a number of species, including the mussel, which it said was particularly threatened.

The mussel, exploited in the search for pearls, is now extinct in two-thirds of the 155 Scottish rivers it occupied a century ago.

Craig Macadam, Scotland director of Buglife, said: "As a nation, we have an international responsibility to safeguard the future for this species."

The RSPB said it was concerned that despite being a protected species, the mussel "continues to be threatened by illegal activities".

Some 90% of all freshwater pearl mussels, which can produce valuable pearls, died out in Europe in the 20th century.

Buglife has pinpointed the reasons for the mollusc's decline in a new dossier that says one-third of them are unable to reproduce due to deterioration in the freshwater ecosystem.

Buglife say all but one of the remaining colonies are considered small and vulnerable and, despite full legal protection, they continue to be threatened.

Since 1998, illegal pearl fishing and disturbance of their habitat has played the largest part in their decline, Buglife says.

However, it adds the mussel is also coming under increasing threat from illegal activities, with 72 suspected criminal incidents in the last 14 years in Scotland – 45 of which occurred in the last four years.

Despite the number of incidents reported, only two cases were reported to the procurator- fiscal. One failed to proceed due to insufficient evidence and the other resulted in fines totalling £15,000 imposed on two individuals and a company.

The RSPB said it welcomes action taken in February when Shawater, the firm behind a supposedly green energy scheme 12 miles from Aberfeldy, Perthshire, was fined £4000 for wiping out hundreds of the rare mussels with pollution.

However, officials added they was concerned similar illegal activities go undetected or unenforced.

"Effective and co-ordinated action is urgently needed to prevent illegal pearl fishing and to protect existing pearl mussel habitat," the wildlife charity said.

Mr Macadam added: "Further controls are required on illegal pearl fishing, through limiting the trade and encouraging the reporting of suspicious activity across Scotland."