Pearl lure threat to river mussels

By Lorna Gordon Scotland correspondent, BBC News

Each pearl can be worth hundreds of pounds to the thieves

In a burn in the Highlands where the water is coloured brown by peat, scientists are keeping watch over a small colony of freshwater pearl mussels.

They've been reintroduced in an effort to reverse a dramatic decline in the species.

In amongst the dark stones on the river bed they are hard to spot.

Despite that, their location is being kept secret.

Freshwater mussels are increasingly targeted by thieves who kill all the mussels they gather in the hope of finding a precious pearl inside.

64,000 years

Last year, shells discarded by poachers pointed to at least 15 kills on Scotland's rivers.

That's dramatically up on the previous year.

Dr Peter Cosgrove, an ecologist who has spent years surveying Scotland's freshwater pearl population, believes even this may be the tip of the iceberg.

Ecologist Peter Cosgrove says the mussel populations are at risk

"We found a kill of 800 mussels, where the average age of each mussel was 80 years old," he said.

"If you do the maths that's 64,000 years of mussel growth, just ripped from a river and destroyed. The rivers just cannot sustain that."

Throughout the world there are now only 150 rivers where there are known populations of breeding freshwater pearl mussels.

Up to half of those rivers are in Scotland.

The mussels play an important role in river ecology, filtering up to 50 litres of water a day.

Those populations remaining have been protected by law since 1998.

Hefty fines

According to Doug Darling from Grampian Police, the thieves are "well versed in what they are doing".

"They know where and when to hit, when there is the least amount of people on a river to see them and catch them."

He adds they can decimate a stretch of river in as little as half an hour.

The penalty for those caught killing a single mussel is as high as