Survival probabilities of plaice, sole and turbot discarded by beam trawl and flyshoot fisheries

• Main Authors: Schram, Edward, van de Pol, Lennert, van Mens, Allard, van Dalen, Pim, Suykerbuyk, Wouter, Cornelisse, Suzanne, Mattens, Alessa, Molenaar, Pieke
• Format: Report
• Language: English
• Published: Wageningen Marine Research 2023
• Subjects: Life Science; Turbot
• Online Access: https://research.wur.nl/en/publications/survival-probabilities-of-plaice-sole-and-turbot-discarded-by-bea; https://doi.org/10.18174/638979

The objectives of this study were 1. to establish baseline survival probabilities for undersized plaice, sole and turbot discarded by tickler chain beam trawl fisheries with two 12 m wide gears and for plaice discarded by flyshoot fisheries, and 2. to establish the effect of replacing the conventional mesh lengthener and cod-end of a 12 m wide tickler chain beam trawl by a modular harvest system (MHS) on discards survival probabilities of undersized plaice, sole and turbot. Discards survival was measured by captive observation of test fish sampled at sea during regular commercial beam trawl and flyshoot fisheries. During all trips, control fish of the same species were used to separate potential effects of the experimental procedures on mortality from fisheries-induced mortality. Average survival of control fish was 83.7% for plaice employed in the flyshoot trips and 86.8% for plaice, 83.3% for sole and 100% for turbot employed in the beam trawl trips. We conducted three trips with a flyshooter in April, May and July 2023 and sampled a total of 675 plaice. Discards survival probability estimates ranged from 39.7% in April to 1.2% in July. The overall survival probability estimate based on these three trips is 15.0% (95% confidence interval 12.5%-17.9%). We conclude that plaice discards survival is highly variable in flyshoot fisheries for reasons that are not yet fully understood. We conducted five trips with a tickler chain beam trawler with two 12 m wide gears in the period February to August 2023. During two out of these five trips we tested the effect of the Modular Harvesting System (MHS) on discards survival. The MHS is a novel cod-end consisting of a membrane-like fabric tube with escapement holes that replaces the mesh cod-end of a trawl. The MHS aims to reduce fish damage during trawling, haul back and unloading. Based on the strong relation between the condition in which fish are discarded and their survival probability, this was predicted to increase discards survival probabilities. To test the MHS, ...