Spatio-temporal composition of discard associated with the deep water rose shrimp fisheries (Parapenaeus longirostris, Lucas 1846) in the south-central Mediterranean Sea

Discarding in fisheries is the fraction of the total catch brought on board and returned to the sea dead or alive for legal or economic reasons. The reduction of discard is one of the main objectives of the European Common Fishery Policy. This study aimed to improve the current knowledge of the discard associated with the deep-water rose shrimp (DPS) fisheries in the south-central Mediterranean Sea. We analyzed data collected from January 2009 to December 2013. Multivariate data analysis and generalized additive models (GAMs) were used to assess the spatio-temporal composition of the discard (which represented 36% of the total catch) and factors influencing its distribution. Multiple analysis of variance highlighted the significant effect of depth factor on discard assemblage. Moreover, in general, bony fish were the most discarded organisms (23.5%), while cartilaginous fish, crustaceans and other invertebrates represented approximately 13% of the total catch. GAMs showed that the fraction of discard in the catch presented significant variation regarding the years, depth and fishing ground. Although the negative trend in discard suggested that the DPS fisheries are moving towards a more sustainable exploitation, the discard fraction in some areas/assemblages remains high. Our results showed that most of the discard was due to species that had a minimum legal size (Hake, DPS, Trachurus spp.), and consequently would be subjected to the European discard ban. In order to improve the fisheries management, specific measures aimed to minimize the unwanted catches of undersized species need to be implemented.