Elevated salinity and isotopic composition of fish otolith carbonate:: stock delineation of pink snapper, Pagras auratus, in Shark Bay, Western Australia

Analysis of stable isotopes of oxygen and carbon in the otolith carbonate of pink snapper, Pagrus auratus, from several locations in Shark Bay, Western Australia, indicated that snapper are highly location specific. The hypersaline (36 to > 60%) Shark Bay, on the coast of Western Australia, generated strongly characteristic isotopic signatures in the otolith carbonate of snapper collected from the various locations indicating low levels of individual movement of the species. Oxygen isotopes showed enrichment in 180 in otolith carbonate with salinity (0.10: A delta(18)O/Delta salinity %.) typical for the evaporation of seawater. The enrichment in C-13 (Up to 1.75%) was attributed to the incorporation of metabolically derived CO2 from an enrichment of C-13 in the food web within Shark Bay. This was possibly a result of lower concentrations of dissolved CO2 with increasing salinity causing a reduction in isotope fractionation during photosynthesis. Results complement recent genetic and tagging studies and provide further evidence of the complex nature of snapper stock structure in the Shark Bay region.