By-catch species susceptibilities and potential for survival in Algarve (South Portugal) deep-water crustacean trawl fishery

• Autor(a) principal: Adão, Ana Catarina Vasconcelos
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/10424
• topic: Rejeições; Tempo-para mortalidade e vitalidade; Características biológicas; Sobrevivência; Arrasto de fundo; Algarve

Bottom trawling for crustaceans in Portuguese coastal waters constitutes a rather important fishery in revenue terms, despite its clear negative impacts on deep-sea communities and marine ecosystems. This poorly selective harvest strategy catches large amounts of unwanted species that are thrown overboard for various reasons. However, survival of discards is not yet properly assessed and constitutes an essential parameter for the upcoming landing obligation, with an exemption for species with “high survival”. In this work, time-to-mortality and a vitality assessment were used to estimate immediate mortality and identify important biological characteristics on the susceptibility of a group of 14 by-catch species, most with commercial interest (Conger conger, Galeus melastomus, Helicolenus dactylopterus, Lepidorhombus boscii, Lophius budegassa, Lophius piscatorius, Merluccius merluccius, Micromesistius poutassou, Mullus surmuletus, Phycis blennoides, Scyliorhinus canicula, Trigla lyra, Trachurus trachurus and Trachurus picturatus). Only S. canicula and C. conger were identified as species with potential to survive after the discarding process. Present results on time-to-mortality show significant differences when comparing individual sizes for some species, with smaller individuals dying faster than larger ones. Furthermore, species with scales, gas bladder and high metabolic rates are more vulnerable to die after being discarded. A short captive observation experiment with C. conger was conducted, with 84% survival after 65 hours of monitoring. However, this survival rate is likely to be overestimated due to two facts: 1) the mortality rate did not stabilize at the end of the experiment; and 2) the majority of individuals showed severe injuries (scratches, bruises and deep wounds). These outcomes can help to identify species that will likely survive the discarding process, factors influencing its survival and provide reliable estimates of unaccounted fishing mortality, essential for stock management and conservation.