LATITUDINAL VARIATION IN FISH RECRUITS IN NORTHWEST EUROPE

In many fish species, ambient temperature is known to govern larval du ration and, therefore, interannual variation in temperature can act to induce variation in reemit numbers. In general, interannual variation in water temperature increases with latitude. It may be expected, the refore, that variation in fish recruit numbers will increase with lati tude along the coastlines of Northwest Europe. Variation in stock and subsequently in egg numbers is also believed to increase from the geog raphical centre of a species' range of distribution towards the border s. It has been hypothesized that the combination of these two sources of variation will yield low variation in reemit numbers near the geogr aphical centre, high variation at the northern edge and intermediate V ariation near the southern edge of the distribution range. We tested t he predicted patterns in recruit variation by examining the relationsh ips between latitude, temperature and the variation in recruit numbers in time series of four flatfish (dab, flounder, plaice and sole) and four roundfish species (cod, bib, poor cod and whiting). Data on inter annual variation in recruit numbers were obtained for sampling sites r anging from Hinkley Point and the English Channel in south England to the continental coast of the southern North Sea, the Marsdiep tidal in let, and the Skagerrak in the north. The data were analysed for: (I) c orrelations between interannual variation and latitude; (2) interannua l variation in recruits in relation to distance of the sampling site f rom the geographical centre of the species distribution; and (3) varia tion in interannual recruit numbers in response to the combination of these two sources of variation. The patterns of variation observed did not correspond with the expectations. In plaice and poor cod the sign of the correlation between recruit variation and latitude was opposit e to the prediction. All other species examined showed no significant variation in recruit numbers in relation to the Variables considered. We neither accept nor reject the hypothesis, however, because the expe cted relationships between the coefficient of Variation in recruits (C VR) and latitude may have been overruled by other sources of variation such as actual water temperatures, sampling methods, average age of t he catch, inshore-offshore gradients and possibly northward shifts of species ranges. (C) 1998 Elsevier Science B.V. All rights reserved.