DYSTROPHY EFFECTS ON THE LIZA RAMADA (RISSO, 1826) (PISCES, MUGILIDAE) POPULATION IN THE CABRAS LAGOON (CENTRAL-WESTERN SARDINIA)

Fish samples were collected between 1999 and 2002 in the Cabras lagoon, the largest brackish area in Sardinia and one of the most important areas for the artisanal lagoon fishery in the Mediterranean area. Because of its natural connection with both the Oristano Gulf and the 'Mare e Foghe' river, in which pollution problems are frequent, this area suffers from dystrophic crises linked to phytoplanktonic or macrophytes blooms. The effect of the 1999 dystrophy on the fish population was studied by analysing the commercial landings variations and the modification of the demographic structure of the most important species, Liza ramada. Because of the dystrophy, the yields have decreased by about 90% since 1998. These effects are most likely attributable to the reduction in recruitment as the VPA analysis on L. ramada suggests. The calculated growth parameters of Thinlip mullet, which are the first reported for a Sardinia lagoon, are useful for fishery management of these areas. The study leads us to conclude that the trophic conditions probably changed, causing the reduction in the natural lagoon's 'call-effect' of recruits from the sea.