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- By-catch species susceptibilities and potential for survival in Algarve (South Portugal) deep-water crustacean trawl fisheryPublication . Adão, Ana Catarina Vasconcelos; Borges, Teresa C.; Breen, MikeBottom 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.
- By-catch species susceptibilities and potential for survival in Algarve (southern Portugal) deep-water crustacean trawl fisheryPublication . Adão, Ana Catarina; Breen, Michael; Eichert, Moritz; Borges, Teresa C.Bottom trawling for crustaceans in Portuguese coastal waters is an important fishery in terms of revenue, despite its negative impacts on deep-sea ecosystems. This fishery catches large amounts of unwanted species that were discarded for various reasons before the introduction of the Landing Obligation, which banned the discarding of regulated species. However, where it can be demonstrated that a species has an acceptably high likelihood of survival, exemptions to this ban may be granted. In this study, time-to-mortality was used to estimate immediate mortality rates and identify important biological characteristics determining the susceptibility 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 piciuratus). Species with potential to survive after the discarding process were identified and a short-term survival assessment of conger eel (Conger conger) was performed. The results suggest that species with scales, gas bladder and high metabolic rates have higher post-discard mortality. Size was a critical factor determining survival in some species, with smaller individuals dying faster. The short-term survival rate of conger eel was determined to be 84% (95% Cl: 75.5 to 93.3%). The methodology and results from this study can help identify species that may survive the discarding process and factors influencing their survival.