Survival probabilities of thornback and spotted rays discarded by beam trawl and flyshoot fisheries

• Main Authors: Schram, Edward, van de Pol, Lennert, Molenaar, Pieke, van Mens, Allard, Bleeker, Katinka, Molla Gazi, Karolina, van Dalen, Pim, Suykerbuyk, Wouter, Batsleer, Jurgen
• Format: Report
• Language: English
• Published: Wageningen Marine Research 2023
• Subjects: Life Science; Tac; The Landing; Common skate
• Online Access: https://research.wur.nl/en/publications/survival-probabilities-of-thornback-and-spotted-rays-discarded-by; https://doi.org/10.18174/629246

Elasmobranchs (i.e. sharks, skates and rays) play an important role as predators in marine ecosystems. In the last century the abundance of several skates and rays in the North Sea declined. Their specific life-history traits, i.e. being long-lived, showing slow growth, late sexual maturity and producing a small number of young per year, make them vulnerable to fishing, pollution and changes in essential habitats, especially spawning and nursery areas. Since 2010 a recovery in the abundances of some species is observed. Landings of skates and rays in European waters are generally managed by a group-TAC, meaning several species are managed under a single Total Allowable Catch (TAC). In the North Sea this group-TAC applies to thornback (Raja clavata), blonde (Raja brachyura), spotted (Raja montagui) and cuckoo ray (Leucoraja naevus). Landings of starry ray (Amblyraja radiata) and common skate (Dipturus sp.) are prohibited. In Dutch fisheries, skates and rays are mainly caught as by-catch in the mixed demersal fishery for flatfish, with landings dominated by thornback ray. For these species the rays below minimum landing size and catches that exceed the vessel’s weekly trip limits are discarded. Since 2019 this practise of discarding has been restricted for all quota regulated species, including rays, by the implementation of a landing obligation under the Common Fisheries Policy (European Union, 2013). The objective of the landing obligation is to create an incentive for fishers to avoid unwanted bycatches and thereby reduce discards rates. The European commission granted a temporary ‘high survival’ exemption for rays and indicated that for this exemption to be renewed or extended beyond 2023, knowledge gaps regarding discards survival probabilities of rays, as laid out in the “Roadmap skates and rays”, need to be filled. The current study therefore aims to contribute to this roadmap by filling main gaps in our knowledge on the survival probability of rays when discarded by the most important Dutch demersal ...