Traps as tools for monitoring deep-sea ecosystems and promoting sustainable fishing

The Norway lobster (Nephrops norvegicus) and the deep-sea blue and red shrimp (Aristeus antennatus) are among the most valuable fishing resources in the Mediterranean Sea. Both species are caught by bottom trawling, which causes significant ecological disturbance in deep-sea environments. This study investigates the viability of traps as a sustainable alternative for their capture. Experimental trap surveys were conducted in two geographical subareas (GSAs) of the western Mediterranean Sea: one targeting N. norvegicus in the GSA 06 at 350-550 m depth, and the other targeting A. antennatus in the GSA 05 at 550-850 m. We tested two bottom-line-trap designs and three trap types: for N. norvegicus, traps with 12 and 24 mm diamond mesh nets, and for A. antennatus, including also semi-floating traps with 24 mm diamond mesh. Traps were effective for N. norvegicus, particularly using 12 mm traps, although the finest mesh sizes increased bycatch of smaller individuals. In contrast, A. antennatus was not captured, potentially due to species-specific behavioural and operational constraints. Other commercial species, such as Plesionika spp., were effectively caught. Although traps are not a fully viable alternative to trawling, our findings highlight their potential as selective tools for research and monitoring in sensitive deep-sea habitats.