Sizes of discarded commercial species in the eastern-central Mediterranean Sea

Discard practices of trawlers in three main fishing areas in the Ionian Sea (eastern and western coast) and the Cyclades Islands (Aegean Sea) were considered using data obtained on board representative commercial vessels over five consecutive years (786 hauls). The length at which 50% of the individuals were discarded (defined as discard size) was estimated for 29 species using logistic regression. In addition the lengths at which 25 and 75% of individuals were estimated. The discard size seems to be a good measurement to study discarding, to compare differences between areas and to investigate the discarding procedure in relation to minimum landing size. The different cod end mesh size used in Greece and Italy (28 and 40 mm, respectively) has no impact on the discarded sizes of the species, because the skippers tended to retain all marketable species and size (legal or not). In contrast to this procedure, the estimated L50s were very close to the legal sizes in the most cases. The minimum landing size seems to be an effective technical measure in Mediterranean fisheries only in combination with spatial and temporal prohibitions due to the numerous landing sizes that make the monitoring of landings by the authorities very difficult. The estimated discard sizes were probably affected by how strict the authorities were in monitoring the landings, the market demand of the species and other socio-economic aspects of fisheries.