ROV-based monitoring of passive ecological recovery in a deep-sea no-take fishery reserve.

In the context of marine conservation, trawl fishing activity is the most important ecosystem stressor in demersal Mediterranean waters. Limited management measures in bottom trawling have caused deep-sea stocks of the iconic Norway lobster Nephrops norvegicus to decrease over the last decade. This crustacean acts as an umbrella species for co-existing megafauna. Here, we used non-invasive Remote Operated Vehicle (ROV) video-surveys to investigate the status of a pilot deep-sea no-take reserve implemented in the northwestern Mediterranean by quantifying demographic indicators of Norway lobsters and the co-existing benthic community, seafloor restoration, and the presence of marine litter. The results revealed that in the no-take reserve the Norway lobster stock showed higher abundance and biomass, and slightly larger body sizes than in the control area without fishing prohibition. Some taxa, such as the fishes Helicolenus dactylopterus and Trigla lyra and anemones of the family Cerianthidae, increased in abundance. We also observed that all trawling marks were smoothed and most of the seafloor was intact, clear indicators of the recovery of the muddy seafloor. The accumulation of marine debris and terrestrial vegetation was similar in the no-take reserve and the fished area. On the basis of the results of this study, we suggest that the use of no-take reserves might be an effective measure for recovering the Norway lobster stock, its co-existing megafauna community, and the surrounding demersal habitat. We also suggest that ROV video-survey might be a useful, and non-invasive method to monitor megafauna and seafloor status in protected deep-sea environments.

Feeding ecology of a Mediterranean endemic mesopredator living in highly exploited ecosystems.

Knowledge of marine predator trophic ecology is essential for defining their ecological role and trophic position in ecosystems. Based on their trophic habits, sharks and batoids occupy higher and medium trophic levels in the food webs, although differences in the trophic preferences exist between species. They are important organisms in marine ecosystems by maintaining the species below them in the food chain and serving as an indicator for ocean health. In comparison to sharks, batoids usually receive less research attention, with very little diet information available. This is true of the speckled ray (Raja polystigma), one of the three endemic batoids in Mediterranean waters. Here, by combining analyses of stomach contents and stable isotopes, we examined the trophic ecology (dietary composition and trophic position) of this ray in the north-western Mediterranean Sea. We also compared its trophic niche with the trophic position of other sympatric elasmobranchs present in same marine ecosystem. The results revealed that R. polystigma mainly consumes shrimps and to a lesser extent crabs, fin-fish, cephalopods, polychaetes and, surprisingly, small demersal sharks. We also found that R. polystigma shows similar trophic position to other crustacean-consumer elasmobranchs such rays and small demersal sharks. The results of this study provide new insights into the ecological role of this endemic ray species in the Mediterranean Sea.