Fish caught in the North Sea have been found to be smaller than they were in 1970.
From then until 2008, the length of fish such as haddock, whiting, herring, and plaice, has decreased in size by as much as 29%.
Scientists warn that the reduction may have been caused by a rise in water temperatures which have increased by between 1 and 2ºC.
Other factors which could have brought about the change include the availability of food and an increase in fishing.
But scientists at the University of Aberdeen lean towards climate change, and particularly warmer waters, because the fall in the size has taken place across a range of species, pointing to one common factor.
''What is interesting is that this was detected across a range of fish species eating different diets, living at different depths and experiencing different levels of fishing mortality,” according to research leader Alan Baudron.
Cod, on the other hand, has remained the same size and sole reduced by only 1% over the period studied.
Warmer waters cause fish to mature earlier but not to continue growing, according to the researchers.
Dr Baudron said: ''Because fish are cold-blooded animals, their metabolic rates are determined by the ambient temperature. In general, fish grow more rapidly during their early life when temperatures are warmer.
''The consequence of rapid juvenile growth is that they become mature at a smaller length and therefore don't grow as large as they would have in colder waters.''
