Growth and condition indices in juvenile sole Solea solea measured to assess the quality of essential fish habitat

We used growth rates (estimated from otolith microstructure), morphometric (Fulton's K condition index) and lipid (triacylglycerols: sterols ratio, TAG:ST) condition indices measured on 0-group juveniles of common sole, to compare the habitat quality of 7 nursery grounds with differing levels of anthropogenic pressure. Along the French coast of the Southern Bight of the North Sea and the Eastern English Channel, we compared 2 sites located in intensively developed and industrialised harbour areas (Dunkerque and Calais), 1 site in a medium and less industrialised harbour (Boulogne), 1 site near a large and polluted estuary (Seine) and 3 other sites located near small estuaries less subject to human pressure (Canche, Authie and Somme). Indicators of human disturbance as well as hydrological and biotic data were used to establish between-site differences in environmental quality. Our results indicate consistent differences in the growth and condition indices of 0-group sole among the 7 sites. Sole had the slowest growth (mean G = 0.54 mm d(-1)) and lowest condition indices (mean K 1.07; TAG:ST = 0.32) at Dunkerque and Calais and the fastest growth (mean G = 0.70 mm d(-1)) and highest condition indices (mean K = 1.19; TAG: ST = 2.18) at the Authie, Canche and Somme estuaries. The indices measured in this study correlated well with anthropogenic disturbance and may provide a useful tool to assess habitat quality. Sites with highest sediment chemical contaminants had the lowest habitat quality and, through growth and lipid-storage limitation, could dramatically lower over-winter survival of the juveniles living in these nursery grounds.