When the Trawl Ban Is a Good Option: Opportunities to Restore Fish Biomass and Size Structure in a Mediterranean Fisheries Restricted Area

This paper reports the results of a 15-year trawl ban imposed in 1990 in the Gulf of Cas-tellammare (GCAST: NW Sicily, central Mediterranean Sea) and its effects on the biomass and sizestructure of demersal finfish and shellfish and on the proportion of different commercial categoriesof fish. Data were collected by experimental trawl surveys conducted in the GCAST and in twotrawled areas before and after 1990. The biomass of the total assemblage and of a number of selectedspecies was significantly higher in the GCAST after the ban. Highly commercial species had thelargest increase in the same gulf after the ban, particularly at the depths used by artisanal fishermen.The results from size-based indicators were not as clear-cut as those from biomass though. Althoughthe length frequency distributions obtained in the GCAST were significantly different from theother gulfs, in several cases, the values of the size indicators were higher in the trawled gulfs. Ourresults suggest that, at the temporal and spatial scale adopted, trawl bans may drive full biomassrecovery but only partial size structure recovery of the fish populations subject to trawl exclusion,at least in the Mediterranean. The trawl ban in the Gulf of Castellammare provides an example ofan effective ecosystem-based fisheries management tool that offers the potential for fish stock re-building and for the economic sustainability of artisanal, small-scale fisheries.