Abstract
Knowledge of fish life cycles is important for exploited species. In the Mediterranean Sea, catches of common sole ( Solea solea ) have fluctuated widely since the 1970s. Solea solea displays an ontogenetic shift in habitat: sole larvae are marine, juveniles inhabit shallow marine waters and coastal lagoons and adults inhabit deeper marine waters. Although the results of this study were obtained using only a small set of individuals, the otolith elemental composition and isotopic ratios were investigated for the three life stages (post-larval, juvenile and adult) in order to acquire a better knowledge of the variability in environmental conditions experienced by the common sole at each life stage in the NW Mediterranean. Moreover, this study provides the first evaluation of the potential of whole otolith microchemistry for investigating habitat connectivity in sole populations from the Gulf of Lions. The elemental and isotopic signatures of otoliths of post-larvae captured in various environments appear to show variations related to the River Rhone inputs (high Ba/Ca and low Sr/Ca ratios). Juveniles appear to show significant variations in otolith elemental and isotopic compositions depending not only on the physico-chemical properties of water in the nurseries they inhabit (Rhone River, Thau or Mauguio lagoons), but also as a result of variations in the chemical composition of their surrounding sediments and in their benthic prey. Adults exhibit otolith differences for isotopic ratios only, which is probably linked to the River Rhone inputs. Finally, several significant relationships were observed between otolith elemental composition and fish size in specimens captured at the River Rhone mouth. However, these variations seem to be an indication of the composition acquired in each environment rather than a sign of ontogeny.
Highlights
Many marine fish species are subject to intensive fishing and stocks are overexploited (Garcia et al 1999, Myers and Worm 2003)
Solea solea displays an ontogenetic shift in habitat: sole larvae are marine, juveniles inhabit shallow marine waters and coastal lagoons and adults inhabit deeper marine waters
The results of this study were obtained using only a small set of individuals, the otolith elemental composition and isotopic ratios were investigated for the three life stages in order to acquire a better knowledge of the variability in environmental conditions experienced by the common sole at each life stage in the NW Mediterranean
Summary
Many marine fish species are subject to intensive fishing and stocks are overexploited (Garcia et al 1999, Myers and Worm 2003). In coastal environments many fish migrate between habitats during larval, juvenile and adult stages. These coastal environments are subject to significant pressures in addition to fishing, such as pollution and eutrophication, which lead to habitat loss (Nixon 1995, Kemp et al 2005). The life cycle of the common sole is characterized by an ontogenetic shift in habitat (Salen-Picard et al 2002), with juveniles inhabiting coastal lagoons and shallow coastal marine waters (≤10 m), whereas older individuals occupy the continental shelf from 20 to 150 m depth. A recent study based on otolith shape analysis (Mérigot et al 2007) showed that several local populations of sole inhabit the Gulf of Lions. The exact nature of past environmental changes or migrations is invisible in the studies of otolith shape
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