Stock assessment of some coastal species caught by artisanal fishery (SACS)

This report illustrates the results of the project "Stocks assessment of some coastal species caught by artisanal fishery" (SACS), (MED 96/054), whose main objectives were: 1. To study the structure of the artisanal fleet; 2. To study the activity of the artisanal fleet in time and space; 3. To study the qualitative and quantitative composition of the artisanal fleet's catch in time and space, for each fishing gear category, in the study area; 4. To study the quantities unloaded (landings) and the quantities thrown back (discards) of all the species caught by the artisanal fleet, in time and space, per fishing gear category, in the sample ports; 5. To identify the stocks of Lithognathus mormyrus and Diplodus vulgaris using genetic analysis and/or cluster analysis, and/or neural networks; 6. To determine the size of the stocks of Lithognathus mormyrus and Diplodus vulgaris using a pseudo-Virtual Population Analysis (VPA); 7. To determine the quantities caught by the artisanal fleet in the study area and the relative fishing effort for the main species, on a monthly basis for each type of fishing gear employed; 8. To study the space-time distribution, on a local scale, of Lithognathus mormyrus and Diplodus vulgaris and the space-time behavior of the artisanal fleet per category of gear using geostatistical techniques and GIS (Geographical Information Systems); 9. In addition, each partner studied one species of scientific or local interest: Mazara studied Sarpa salpa, Messina Oblada melanura and Kavala Diplodus sargus. The study area was the strip of sea around Sicily, limited by the 100 m isobath, the strip of Thracian Sea, from Alexandroupoli to Olympiada, between the coast and the bathymetric level of 100 m, and the strip of sea surrounding the islands of Thassos and Samothraki within the isobath of 100 m. The project started on June 16th 1997. The first coordination meeting was held in Mazara del Vallo from July 3rd to 5th 1997. A frame survey was carried out on the whole study area, during the first three months of the project, to define ports and landing places and to take a census of the target fishing fleets. In all, 83 ports and landing places were counted; 54 in Sicily, with 1727 artisanal fishing boats, and 29 on the Thracian Sea, with 702 artisanal fishing boats. Based on the outcome of the frame survey, 22 sample ports or landing places (SP) were selected according to a stratified random design with a selection probability proportional to the respective numbers of boats (though some ports - but not more than one per stratum - were deliberately chosen); the sample included 11 ports in Sicily and 11 on the Thracian Sea. Catch-effort surveys were subsequently conducted at each SP: twice a month a sample of fishermen was interviewed at landing to collect detailed data on fishing effort, gear used, areas fished and species caught (both qualitatively and quantitatively). At 5 SP in Sicily and 4 SP on the Thracian Sea, samples of Lithognathus mormyrus, Diplodus vulgaris and other species of local interest were bought at landings once or more a month (depending on meteorological conditions and abundance of catches). The fish samples were processed in the laboratory to collect all biological and biometric parameters. In addition, samples of Lithognathus mormyrus and Diplodus vulgaris were bought at 4 Sicilian and 2 Thracian Sea SP for genetic analysis (for the purpose of stock identification). Estimates of total catch, fishing effort and CPUE were produced for both the Sicilian and the Thracian sea study areas on a seasonal basis. In addition, the total catch and CPUE per season were estimated in both areas for each of the following species or groups of species: Diplodus sargus, Diplodus vulgaris, Diplodus spp. (other), Sarpa salpa, Lithognathus mormyrus, Oblada melanura, Sepia officinalis, Dicentrarchus labrax, Homarus gammarus, Loligo vulgaris, Mullus barbatus, Mullus surmuletus, Octopus vulgaris, Palinurus elephans, Penaeus keraturus, Solea spp., Scorpaena spp., Seriola dumerili, Trachurus spp., Chondrichthyes. 6 Stock and population dynamics of Lithognathus mormyrus and Diplodus vulgaris were assessed by an age-based Virtual Population Analysis (ACA-VPA). Finally, cartographic representations of both total catches and fishing effort at each SP were produced using a Geographical Information System (GIS). By September 30th 1999, 690 sampling days and 4199 interviews had been collected in Sicily whilst 549 sampling days and 3887 interviews had been recorded on the Thracian Sea. In all, the project involved 17 fishery biologists, 5 biologists, 2 physicists, 1 chemist, 2 electronic engineers, 1 environmentalist, 1 oceanographer, 1 statistician, 1 economist, 11 technicians, 7 students, and 5 field operators.