Knowing the displacement capacity and mobility patterns of industrially exploited (i.e., fished) marine resources is key to establishing effective conservation management strategies in human-impacted marine ecosystems. Acquiring accurate behavioral information of deep-sea fished ecosystems is necessary to establish the sizes of marine protected areas within the framework of large international societal programs (e.g., European Community H2020, as part of the Blue Growth economic strategy). However, such information is currently scarce, and high-frequency and prolonged data collection is rarely available. Here, we report the implementation of autonomous underwater vehicles and remotely operated vehicles as an aid for acoustic long-baseline localization systems for autonomous tracking of Norway lobster (Nephrops norvegicus), one of the key living resources exploited in European waters. In combination with seafloor moored acoustic receivers, we detected and tracked the movements of 33 tagged lobsters at 400-m depth for more than 3 months. We also identified the best procedures to localize both the acoustic receivers and the tagged lobsters, based on algorithms designed for off-the-shelf acoustic tags identification. Autonomous mobile platforms that deliver data on animal behavior beyond traditional fixed platform capabilities represent an advance for prolonged, in situ monitoring of deep-sea benthic animal behavior at meter spatial scales.

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.

The increasing global demand for marine resources raises concerns about sustainable resource management and biodiversity conservation. Spatial closures, such as marine protected areas, can be valuable tools for maintaining and restoring exploited populations. When these spatial closures adopt a dynamic nature being adapted to the changing environment, they can effectively account for factors such as shifting species distributions, which enhances their potential to achieve ecological and socio‐economic objectives. Here, we adapted a decision‐support tool (the software Marxan), typically used for selecting static and permanent areas, to produce management recommendations that integrate permanent and temporal closures to fisheries. Our aim was to compare the outputs of a static network of permanent no‐take reserves with four other dynamic scenarios, including permanent and temporal closures that account for seasonal variations in the populations of species. All scenarios prioritized sites for the conservation of one of the most valuable European fishing stocks, the Norway lobster (Nephrops norvegicus). Additionally, we considered 12 other commercially exploited species captured by the Norway lobster fishery. The assessed outputs included retained biomass, area extent, closure type (permanent and seasonal) and opportunity costs within each scenario. We observed that all dynamic scenarios required fewer management areas permanently closed than the static scenario. This resulted in a lower opportunity cost for fisheries but also a higher capacity for biodiversity conservation. Therefore, complementing permanent with temporal closures could enhance biodiversity conservation and fisheries management. The novel dynamic planning method presented here could be applicable to other species, ecosystems and socio‐economic contexts.

The Norway lobsterNephrops norvegicusis one of the most important marine resources for European fisheries. However, overfishing has caused the stocks to decline over the last decades, particularly in the Mediterranean Sea. The implementation of no-take marine reserves could change these current trends, thus achieving a more sustainable fishery. The effectiveness of no-take reserves depends on optimal size design, and because of this, new behavioural data on the spatial ecology of the species are of pivotal importance. Here, for the first time, we investigated the spatial movements and daily activity patterns of Norway lobster in a deep-water (315-475 m depth) no-take marine reserve of 10 km²in the continental slope of the northwestern Mediterranean Sea, by combining acoustic tracking and tagging-recapture procedures. The results revealed the territorial behaviour of Norway lobster, centred in small exclusive individual areas where most displacements took place at midday. We found that once settled in a place, their home ranges reached approximate sizes of 17.75 to 736.25 m², suggesting that no-take marine areas focussed on recovering Norway lobster populations do not require large extents to be effective. Tag-recapture data indicated minimal spillover of biomass, implying that Norway lobsters are site settled and do not perform large movements. Future studies on larval spread and recruitment would be necessary to focus on the possible spillover benefit for fisheries. The acoustic telemetry system used in the present experiment effectively revealed the range of movement of individuals, and thus represents a promising monitoring tool to assess no-take marine reserve sizes and reciprocal spacing for deep-water demersal resources.

One of the main drivers of marine ecosystem change is fishing activity, bottom trawling being the most intensive fishing practice affecting benthic ecosystems worldwide. In the western Mediterranean Sea, Norway lobster stocks present signs of overexploitation due to trawling pressure, as their biomass and abundance have decreased abruptly during the last few years. No-take fishery reserves, a type of marine protected area where fishing is prohibited, could be efficient management measures to recover Norway lobster overexploited populations and coexisting demersal megafauna. Adopting a BACI (before–after control–impact) approach, we performed experimental fishing surveys before and after 4 years of the implementation of a deep-sea no-take reserve in the northwestern Mediterranean. After 4 years of closure, the Norway lobster population increased in abundance, biomass, body size, and trophic level in the no-take reserve. Our approach also revealed an increase in Norway lobster biomass beyond its boundaries, suggesting a spillover effect. Other demersal fish species also increased in biomass and abundance in the no-take reserve. Based on the results of this study, we suggest that no-take reserves might be an effective measure for recovering the Norway lobster stock and some species present in the same habitat.

The Norway lobster, Nephrops norvegicus, is one of the most valuable fishery resources in many coastal countries of the Mediterranean Sea and the northeastern Atlantic Ocean. In the Mediterranean Sea, several stocks are being overexploited, with ecological, economic, and social consequences. To perform an adequate stock assessment and provide guidance on maximum sustainable yield, reliable biological parameters of the species are required. Considering that biological parameters may change over time in overexploited populations, in the present study, we updated key biological parameters for the N. norvegicus stock of the northwestern Mediterranean Sea: size at which 50% (L50) of females were in reproductive condition, length–weight relationship, and individual size structure. Moreover, daily landings were combined with the spatial position of the vessels tracked by their Vessel Monitoring System (VMS), to obtain information on the geographical distribution and time series of Landings Per Unit Effort (LPUE), as well as total landings from 2008 to 2021. Our results suggest overexploitation of the resource, revealing a severe reduction in size at 50% maturity, an earlier spawning and brooding period, and a clear decrease of LPUE over time.