COD stocks might be vanishing but increasing quantities of anchovies and sardines are being found in Scottish waters because of global warming.

The small pelagic fish, which are important commercial species in southern Europe but rare in more northerly waters, have been appearing with steadily increasing frequency in trawl catches off Scotland.

Because of the increase, particularly since 1995, Fisheries Research Services of Aberdeen decided to investigate the phenomenon and compare recent measurements of the fish in the north-western North Sea with those taken in the past.

Trawl data going back to 1925 shows catches of these warm water species increased suddenly after 1995, with relative numbers highest in 1998.

However, Doug Beare, who carried out the research, said the numbers were very low and were not available in commercial quantities.

He said the sea temperature had risen significantly over the past 75 years, with the most pronounced rise in the winter months. Research has shown that over the past 30 years North Sea temperatures have risen by between 1C and 1.5C.

Mr Deare said that although the numbers were quite low they were unprecedented.

''For 70 years you didn't see any anchovies but in the last survey this year we pretty well saw an anchovy a tow,'' he said.

He said it was such a rare occurrence to catch an anchovy in the past that when one was caught with herring in the 1850s off Northumberland it went to the museum at Newcastle University.

He said: ''The changing temperature could be having an influence on the supply of anchovy and sardine food (zooplankton), or a positive effect on egg and larval survival, or it could be the fact that temperature is related to Atlantic inflow, which imports anchovy and sardine eggs into the North Sea from further south.''

Meanwhile, the reputation of the River Dee in the north-east as one of the world's great salmon rivers could be under threat unless a new reservoir is built.

A combination of low rainfall and high temperatures have left thousands of salmon trapped in shallow water on the outskirts of Aberdeen, unable to make their way back up the river to spawn.

Yesterday Ted Brocklebank, Scottish Conservatives' fisheries spokesman, said financial support from the Scottish Executive was required to remedy the long-term problems and safeguard the vital (pounds) 6m industry for the Dee valley.

John Foster, of the Dee Salmon District Fisheries Board, said: ''If we do nothing and summers continue as this year, we are only waiting for a bigger problem.''