The by-catch of sharks in the western Mediterranean (Balearic Islands) trawl fishery

Abstract

The shark species, blackmouth catshark ( Galeus melastomus), velvet belly ( Etmopterus spinax) and coastal spotted dogfish ( Scyliorhinus canicula) are an important by-catch of the Balearic Islands (Western Mediterranean) trawl fishery. The catch compositions of the fishery taking these species is described and analysed in terms of landings and discards. Only two of these species are sufficiently abundant to be recorded in the landings (blackmouth catshark and spotted dogfish). The length compositions in terms of both landings and discards were analysed for these two species. Spotted dogfish catches reached similar proportions to those of the target species in the coastal fishery (red and striped red mullet) and in the shelf trawl fishery (European hake); whereas the catches of blackmouth catshark and velvet belly were a small proportion of the total catch in the slope fishery for red shrimp. The size range of the spotted dogfish was between 7 and 53 cm TL. Juveniles and adults were distributed throughout the whole area, although adults appeared to be more abundant in the coastal zone. The length distribution of blackmouth catshark showed a trend of increasing size with depth; the size range was between 9 and 63 cm TL. For both species, individuals smaller than 35 cm TL were usually discarded. Only 25% by number and 60% by weight of the total spotted dogfish catch was landed. For the total blackmouth catshark catch, the corresponding percentages were 10% by number and 35% by weight. The role of these species as indicators of fishing pressure was investigated, taking into account the differences between the two fishing zones sampled, one with a fleet of 24 trawlers and the other with only 4.