Changes in fish distribution in the eastern North Atlantic: Are we seeing a coherent response to changing temperature?

T he tem perature o f the upper 300 m o f the N orth A tlantic increased by abou t 0.57°C between 1984 and 1999. but this underlying trend was overlain with substantial geographic and in terannual variability. N orthw ard shifts occurred in the distribution o f m any commercial and non-com m ercial fish species in the N E Atlantic during the 1990s. New records were established for a num ber o f M editerranean and N W African species on the south coast o f Portugal. R ed mullet (M ullus surmuletus) and bass (D icentrarchus labrax) extended their ranges northw ard to western N orw ay and catches o f the form er increased th roughout the 1990s in the N orth Sea. A bundance or relative abundance o f w arm -w ater commercial species o f gadoids and flatfish gener­ ally increased during the 1990s, bu t like the warm ing trend the changes in distribution and abundance were by no m eans uniform and there was considerable in terannual variability. There were also examples o f southw ard shifts lo r some species, which can be related to local hydrographic conditions, such as upwelling. Inform ation on distri­ bution and abundance o f G reenland cod (Gadus morhua L.) and N orw egian springspaw ning herring (Clupea harengus) during a previous warm ing period in the late 1920s and 1930s is also presented and com pared with changes in the 1990s.