Physiological recovery after bottom trawling as a method to manage discards: The case study of Nephrops norvegicus and Squilla mantis

Abstract

The European Fisheries Policy aims at a progressive elimination of discards. An exception from this regulation includes the release of species with high survival rates after capture. In south-western Atlantic waters of Europe, Norway lobster (Nephrops norvegicus) and spottail mantis shrimp (Squilla mantis) are amongst the most important crustacean species captured by bottom trawling. We evaluated their short-term survival probability, survival rates and recovery capacities after being trawled by an oceanographic vessel. Seasonal differences were considered by sampling in spring and autumn. In order to characterise the full recovery after capture, physiological responses were also analysed along a time-course of 24 h. Our results confirm that bottom trawling is a stressful process to these crustacean species, as seen by changes in plasma and muscle metabolites, hemocyanin and immune system parameters. However, maintaining captured animals in onboard water tanks evidenced the full physiological recovery of survivors after 6 h and before 24 h. Survival in Norway lobster and spottail mantis shrimp varied according to the season, being higher in spring (68.4 ± 7.1% and 87.0 ± 4.7%, respectively) than in autumn (33.8 ± 7.8% and 63.8 ± 9.3%, respectively), probably due to the higher temperatures registered after summer months. The employment of the presented techniques for the evaluation of other crustaceans, fishing gears and geographical areas can be contemplated. Fisheries stakeholders might use this approach to better manage discards in Europe.