The stable carbon and nitrogen isotopes and fatty acid composition of tapertail anchovy (Coilia mystus) at four migration stages collected around the Changjiang Estuary were analysed to investigate the variations in the trophic biomarkers during the fish migration. δ13 C and δ15N values of C. mystus ranged from −21.5 to −15.4‰ and from 6.9–15.8‰, respectively. Both δ13C and δ15N were enriched during migration. Polyunsaturated fatty acids were the dominant fatty acids and the major fatty acids found in C. mystus were C20:5n-3, C22:6n-3, C20:4n-6, C16:0, C18:0, C16:1n-7, C18:1(n-9, n-7) and C20:1 + C22:1. Significant changes among C. mystus at different migration stages were found both in the fatty acid composition and specific fatty acid concentration. Though the enrichment of stable isotopes may due to multiple factors (e.g. diet shift, environment and ontogeny), the dietary influence can be determined by the variation in fatty acid composition. Changes in the concentrations of benthic markers (C18:1n-7 and C20:4n-6) and pelagic markers (C18:1n-9 and C20:1 + C22:1) in C. mystus during the migration may suggest that benthic and pelagic food sources alternately dominated the anchovies' diet during different migration stages. It seems that application of multiple biomarkers in the trophic study of migratory fish will elevate the reliability of the analysis.

Members of the Epinephelinae subfamily of serranids (‘grouper’) are heavily exploited by bottom longline in the Gulf of Gabès located in the south of Tunisia. In addition to direct mortality, hook and release mortalities likely occur when fish are caught and released, due to injuries sustained from hooking as well as those associated with retrieval. During five experimental trips (29 fishing sets) conducted in August 2011 from the port of Djerba (south of the Gulf of Gabès), we evaluated the effect of hook styles (9/0 ‘J’ and 12/0 circle hook) on groupers and non-target species. A total of 340 specimens representing 10 species were captured. The higher catch rate was registered for Epinephelus aeneus. The majority of groupers captured were female mature. The circle hook increased the capture of the most common grouper E. aeneus and did not affect the catch of Epinephelus marginatus and Epinepheleus costae. The effect of the type of hook on hooking location was inconclusive. Managing of the grouper fishery using some management actions such as size limits, bag limits, and closed seasons may prevent more unnecessary losses of grouper species. From this preliminary study, a definite conclusion for or against the use of circle hook cannot be drawn. Further research on the role of gear modification and hook designs in reducing by-catch, hooking-related injury and mortality should be encouraged.