Fisheries and their management using artificial reefs in the northwestern Mediterranean Sea and southern Portugal.

Though in the Mediterranean Sea artificial reefs (ARs) are mainly multipurpose structures, the main goal has been the protection and enhancement of fishing resources exploited by sport and commercial fishermen. All around the inshore waters, the main problem is prevention of illegal activity of otter trawlers which destroy the habitats, juveniles and spawners of important commercial species, though trawling is forbidden up to 50 m depth or 3 miles from the shore. The ARs are built with special anti-trawling module armoured or very heavy and large in size. Sometimes, ARs are used to protect natural habitats and in particular valuable, Posidonia oceanica seagrass beds that play a fundamental role as nursery areas, biodiversity, refuge and a source of food, and for traditional small scale fisheries. In the western Mediterranean basin ARs are developed since 1960 in France, Italy, Spain, Portugal and Monaco. A large AR complex, composed of 7 artificial reef systems, have been deployed in the Algarve (southern Portugal). It occupies an area of 43.5 km2 of seabed with more than 20,950 modules weighting 73,000 t and with a volume of 103,000 m3. These ARs have successfully increased the fishing yield and diversified the catches. On the other hand, they increase biodiversity and epibenthic biomass, and have became an interesting recreational diving spot, as well as a site for research. Spain shows the more extensive reef-building activity in terms of number of reefs (103 in 2002) and seabed protected (550 km2). The armed modules (concrete cylinders or square blocks with 4 protruding iron spikes; 3-5 t) used for anti-trawling are effective to prevent illegal fishery but poor in improving hard substrata and microhabitat availability. In France 44,000 m3 of concrete modules were deployed in 20 sites, equally distributed in West and East coast. Eight sites are off the western coast (Languedoc - Roussillon) to protect static fishing gears, longlines and natural habitats from illegal trawling. Extensive colonization by oysters, fish and lobsters on some reefs was reported. In some other ARs more fish than in comparable natural reefs was found. Where small modules (1 - 2 m3) were placed in chaotic heaps of 50 to 100 m3 or so the greatest amount of fish was recorded. In Italy ARs made mainly of concrete perforate cubic blocks were deployed in all the seas with different aims but the best results in terms of harvestable yield were obtained in the middle Adriatic Sea due to heavy settlement and fast growth of molluscs, in particular Mytilus galloprovincialis. Within a four years from deployment the incomes of small-scale fisheries exceeded by three times the initial investment.