The stable carbon and nitrogen isotopes and fatty acid composition oftapertail anchovy (Coilia mystus) at four migration stagescollected around the Changjiang Estuary were analysed to investigate thevariations in the trophic biomarkers during the fish migration. δ13 C and δ15N values of C. mystusranged 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 majorfatty acids found in C. mystus wereC20:5n-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 migrationstages were found both in the fatty acid composition and specific fatty acidconcentration. Though the enrichment of stable isotopes may due to multiplefactors (e.g. diet shift, environment and ontogeny), the dietary influencecan be determined by the variation in fatty acid composition. Changes in theconcentrations of benthic markers (C18:1n-7 and C20:4n-6) and pelagic markers (C18:1n-9and C20:1 + C22:1) in C. mystus during the migration maysuggest that benthic and pelagic food sources alternately dominated theanchovies' diet during different migration stages. It seems that applicationof multiple biomarkers in the trophic study of migratory fish will elevatethe reliability of the analysis.

Members of the Epinephelinae subfamily of serranids (‘grouper’) are heavilyexploited by bottom longline in the Gulf of Gabès located in the south ofTunisia. In addition to direct mortality, hook and release mortalitieslikely occur when fish are caught and released, due to injuries sustainedfrom hooking as well as those associated with retrieval. During fiveexperimental trips (29 fishing sets) conducted in August 2011 from the portof Djerba (south of the Gulf of Gabès), we evaluated the effect of hookstyles (9/0 ‘J’ and 12/0 circle hook) on groupers and non-target species. Atotal of 340 specimens representing 10 species were captured. The highercatch rate was registered for Epinephelus aeneus. Themajority of groupers captured were female mature. The circle hook increasedthe capture of the most common grouper E. aeneus and didnot affect the catch of Epinephelus marginatus and Epinepheleus costae. The effect of the type of hook onhooking location was inconclusive. Managing of the grouper fishery usingsome management actions such as size limits, bag limits, and closed seasonsmay prevent more unnecessary losses of grouper species. From thispreliminary study, a definite conclusion for or against the use of circlehook cannot be drawn. Further research on the role of gear modification andhook designs in reducing by-catch, hooking-related injury and mortalityshould be encouraged.