Iniziativa di restocking del sarago maggiore Diplodus sargus (L., 1758) e tecniche di monitoraggio in un'area protetta con strutture artificiali nel Golfo di Castellammare (Sicilia N/O)

A pilot experiment of marine ranching using hatchery-reared juveniles of white seabream, Diplodus sargus, was made in the Gulf of Castellammare (NW Sicily). The research aimed at evaluating (i) if artificial reefs are suitable for the settlement of reared young seabreams, (ii) what are the main causes of mortality and (iii) the growth rate of released fishes in the open sea. A total of 6930 tagged cultured juvenile white seabreams (305 days old) were released in an artificial reefs (AR) area. Underwater visual census, sightings and recaptures were used as a source of data for estimating abundance and size of released fishes. The survey lasted 15 months and was carried out in artificial (AR, breakwaters and harbours) and natural (river mouths, rocky bottoms and Posidonia oceanica meadows) coastal habitats of the Gulf. A few days after the release, more than 90% of the tagged seabreams left AR and moved mainly towards harbours and breakwaters, which resulted to be particularly suitable for their settlement and growth. The recapture was 8.2% of the released stock. During the first days after releasing, the main ascertained sources of mortality were professional fishing (6.7%) and predation by conger eel, Conger conger (1.1%). A behavioural deficit of the reared seabreams in the use of refugia and food was observed in the initial period following the release. The results obtained provide some management suggestion for the feasibility of marine ranching initiatives involving hatchery-reared fishes.