The temperature of the upper 300 m of the North Atlantic increased by about 0.57°C between 1984 and 1999. but this underlying trend was overlain with substantial geographic and interannual variability. Nor thward shifts occurred in the distribution of many commercial and non-commercial fish species in the NE Atlantic during the 1990s. New records were established for a number of Mediterranean and NW African species on the south coast of Portugal. Red mullet (Mullus surmuletus) and bass (Dicentrarchus labrax) extended their ranges northward to western Norway and catches of the former increased throughout the 1990s in the North Sea. Abundance or relative abundance o f warm-water commercial species of gadoids and flatfish generally increased during the 1990s, but like the warming trend the changes in distribution and abundance were by no means uniform and there was considerable interannual variability. There were also examples o f southward shifts lor some species, which can be related to local hydrographic conditions, such as upwelling. Information on distribution and abundance of Greenland cod (Gadus morhua L.) and Norwegian springspawning herring (Clupea harengus) during a previous warming period in the late 1920s and 1930s is also presented and compared with changes in the 1990s. Article from Marine Science Symposia Vol. 219 - "Hydrobiological variability in the ICES Area, 1990-1999", symposium held in Edinburgh, 8-10 August 2001. To access  the remaining articles please click on the keyword "MSS Vol. 219".