Common sole

Abstract: Shape analyses were carried out on otoliths of the common sole, Solea solea (Linnaeus, 1758), in order to discriminate local populations in the North-Western Mediterranean Sea. Samples were collected in various environments like coastal lagoons, the outlet of the Rhone River as well as other marine sites. Morphological analyses highlighted a significant asymmetry between the left and right otoliths. This character could be acquired during or shortly after settlement on soft-bottoms when the individuals really become flatfishes. The otolith shape was described by seven harmonics from elliptic Fourier descriptors and by five indices of shape (coefficient of form, roundness, circularity, rectangularity, and ellipticity). The existence of several local populations of common sole in the NW Mediterranean was demonstrated. In particular, discriminant analyses highlighted significant differences in otolith shape according both to fish size and to the types of environment in which the fish live, i.e. coastal lagoons vs. marine sites, but also between sites belonging to the same type (lagoons, and marine sites). The differences in shape could be linked (1) to the particular environmental conditions of each site, and (2) to changes in metabolic and/or physiological conditions according to the stage of development of the fish which most likely influences the otolith growth.

Abstract: Levels of arsenic contamination in muscle and liver tissue of 25 sea fish and 4 shellfish species from the North Sea were determined. Analyses were done by both ICP-MS and HG-AFS to distinguish between nontoxic and toxic fractions of As. Highest total As concentrations were found in lemon sole, dogfish, ray, and witch. Average total As concentrations in these fish species were higher than 20 mg kg 1 WW. The same species as well as the other flatfishes contained the highest amounts of toxic As ( 0.1 mg kg 1 WW). Toxic fractions (AsTox/AsT%) above 2% were found in the following six species: seabass, ling, john dory, pouting, dab, and brill. No preferential concentration in the liver compared to the muscle was observed. In a worst-case scenario (when fish has been dried or smoked and the toxic As level is high; for example 0.5 mg kg 1 WW), the As content of North Sea marine food may reach harmful levels. A normalization reflecting the toxic po- tential of sea fish was made. Shark and ray and most flatfish species have positive (high) normalized AsTox values. By ANOVA testing we compared the individual AsT concentra- tions of samples of the same species (intraspecies variability). Significant differences for some fish species were observed; significantly higher AsT concentrations were found in dogfish from the French coast versus the western North Sea and in common sole from the Bay of the Seine, in the north of France, versus the western North Sea.

Abstract: d IFREMER, DYNECO/Ecologie benthique, Centre de Brest, BP 70, 29280 Plouzane, France *: Corresponding author : Abstract: Coastal and estuarine systems are among the most threatened by human activities which damage their ecological function and, in particular, their nursery role for many marine species. In this context, the protection of these vital ecosystems is a critical issue for the management of fisheries resources. To that aim, functional approaches have to be developed that make it possible to assess habitat suitability and quality. The common sole, Solea solea (L.) was selected as an indicator species to identify the features of coastal and estuarine nursery habitats in the Bay of Biscay (France). Previous studies have shown that young-of-the-year (YOY) sole are strongly dependent upon various abiotic factors, and especially bathymetry, sediment cover and the extent of river plumes. We investigated whether taking into account biological variables, based on benthic macrofauna biomasses aggregated into trophic group, may improve the description of the juvenile sole distribution in the Vilaine estuary nursery. Results from Generalised Linear Models demonstrated the importance of integrating these biological variables in the determination of juvenile habitats at a local scale. The abundance of YOY sole was correlated with an index of the benthic invertebrates biomass and, more specifically, with the biomass of suspension feeders. This result was reinforced by a one-dimensional spatial statistical analysis, which pointed out the similar distribution of invertebrate macrobenthos and juvenile sole along the upstream/downstream gradient of the estuary. Moreover, the inter-annual variations of abundance and distribution of juveniles were synchronous with those of the macrobenthos.