Catch and by-catch analyses of tropical tuna fishery in the Gulf of Guinea from 2010 to 2012.

Canned tuna is one of the most widespread and recognizable fish commodities in the world. Over all oceans 80% of the total tuna catches are caught by purse seine fishery and in tropical waters their target species are: yellowfin (Thunnus albacares), bigeye (Thunnus obesus) and skipjack (Katsuwonus pelamis). Even if this fishing gear is claimed to be very selective, there are high levels of by-catch especially when operating under Fish Aggregating Devices (FADs). The main problem is underestimation of by-catch data. In order to solve this problem the scientific community has developed many specific programs (e.g. Observe Program) to collect data about both target species and by-catch with observers onboard. The purposes of this study are to estimate the quantity and composition of target species and by-catch by tuna purse seiner fishery operating in tropical waters and to underline a possible seasonal variability in the by-catch ratio (tunas versus by-catch). Data were collected with the French scientific program ”Observe” on board of the French tuna purse seiner “Via Avenir” during a fishing trip in the Gulf of Guinea (C-E Atlantic) from August to September 2012. Furthermore some by-catch specimens have been sampled to obtain more information about size class composition. In order to achieve those purposes we have shared our data with the French Institute of Research for the Development (IRD), which has data collected by observers onboard in the same study area. Yellowfin tuna results to be the main specie caught in all trips considered (around 71% of the total catches) especially on free swimming schools (FSC) sets. Instead skipjack tuna is the main specie caught under FADs. Different percentages of by-catch with the two fishing modes are observed: the by-catch incidence is higher on FADs sets (96.5% of total by-catch) than on FSC sets (3.5%) and the main category of by-catch is little-tuna (73%). When pooling data for both fishing sets used in purse seine fishery the overall by-catch/catch ratio is 5%, a lower level than in other fishing gears like long-lining and trawling.

Morphological-molecular taxonomy and population genetic structure of common and Egyptian soles of the Adriatic Sea

A total of 352 specimens were analyzed to achieve the different aims of this thesis. 255 central-northern Adriatic specimens of S. solea and S. aegyptiaca were molecularly analysed using microsatellite locus Sos(AC)40 and 205 also morphologically due to evaluate the abundance and the distribution of the cryptic species S. aegyptiaca and to confirm morphologic analyses. Morphological and molecular analyses comparated show a correspondence of 96%. A combined morphologic approach could be proposed to apply multiple criteria on the analyzed external morphological keys. The Adriatic Egyptian soles may lives in shallow waters (up 30 m) and in brackish lagoon. 127 samples of Adriatic common sole added to 326 samples of previous studies showed, using mitochondrial marker (CytB), that the Adriatic Sea as contact zone between Tyrrhenian and Aegean Sea, the divergence within the Adriatic Sea is low but significant between central-north and south, with a longitudinal strong gene flow in central-northern side. It’s also showed as in the Adriatic Sea two near-panmictic populations of common sole exist.