Performance of an excluder grid to mitigate bycatch of sharks in deep-water red shrimp trawl fishery

Abstract

Bycatch of small deep-sea shark species represents a sustainability concern for shrimp trawl fisheries in the Mediterranean Sea. To combat the lack of information on bycatch and efficacy of mitigation measures, this study quantified the capture frequency of shark species and investigated whether a 50 mm bar spacing excluder grid inserted ahead of the small-meshed codend could reduce the bycatch of sharks in the Levant Sea deep-water red shrimp trawl fishery without compromising the catch efficiency of the shrimps. Results from fishing trials demonstrated that bycatch of shark species occurs frequently in the fishery with an estimated capture of 10.9 (CI: 7.2–14.8) velvet belly shark (Etmopterus spinax) and 6.6 (CI: 3.6–9.8) blackmouth catshark (Galeus melastomus) individuals per ∼ 5-hour haul. Further, it was estimated that the capture of these shark species at commonly bycaught sizes could be reduced by 41–57 % if the excluder grid was inserted in the trawl. However, harvestable catch of one of the targeted red shrimps, the blue and red shrimp (Aristeus antennatus) was reduced by 37 % (CI: 8–56 %). Therefore, the tested excluder grid would not be acceptable for the commercial fishery and further design improvements are needed before uptake in the fishery.