SCOTLAND'S rarest breeding duck is facing extinction because brown trout are eating all its food in its last remaining stronghold.

RSPB Scotland says angling could help save the common scoter, which now numbers only around 30 breeding pairs.

The all-dark sea duck bird is only found breeding in the UK at a few locations in the Scottish Highlands, including the Flow Country of Caithness and Sutherland and at some lochs in Inverness-shire.

A study has now shown that the birds thrive best in lochs where there are fewer brown trout, as the fish appear to be eating up the ducks' preferred diet of insects.

Dr Mark Hancock, of the RSPB’s Centre for Conservation Science, which carried out the three-year research project, said that one answer would be to increase angling on certain lochs to give the ducks a greater chance to feed.

He said: "Of all the lochs we investigated during this work, scoters bred most often at those with the shallowest water and the most large, freshwater invertebrates.

"It soon became clear that there were more insects where there were fewer brown trout, so it looks like scoters are being limited by a lack of food in places where the fish are eating it all.

“We're now using these results to design new ways of helping scoters. For example, in areas of the north Highlands where angling activity has dropped off and fish numbers have increased, more trout angling is potentially one way to boost freshwater insect life.

"At hydro lochs, where water levels are to some extent under human control, we could also aim to maximise the area of shallow water.”

The common scoter (Melanitta nigra) breeds in Scotland from May to August. The last official count was in 2007, when there were 52 breeding pairs, but experts estimate numbers have since dwindled to around 30.

The dramatic fall has puzzled researchers as there appear to be plenty of suitable habitats for the species in Scotland.

It was feared the bird could become extinct as a breeding species in Britain, which prompted the study by the RSPB, supported by Scottish Natural Heritage (SNH), the Wildfowl and Wetlands Trust (WWT) and The Conservation Volunteers (TCV).

Hannah Robson, of the WWT, said: “Scoters are amazing birds: an arctic species finding a haven in remote Scottish lochs. This research points to the ways in which we might be able to save them as a fascinating part of our Scottish wildlife heritage.”