Improving the Nordmøre-grid system with an aft open top panel bycatch reduction device for juvenile redfish exclusion in shrimp trawls

Abstract

Shrimp-trawl fisheries often face challenges with bycatch, particularly of juvenile fish species, which can have significant ecological and economic implications. This study evaluated the effectiveness of a low-cost, simple, and innovative open top panel behavioural bycatch reduction device (BRD), positioned aft of the Nordmøre-grid, to reduce juvenile redfish (Sebastes spp.) bycatch while maintaining northern shrimp (Pandalus borealis) catches. Comparative fishing trials were conducted using a twin-trawl setup to compare the experimental trawl against a traditional shrimp trawl. Results demonstrated a significant 54 % reduction in juvenile redfish bycatch for the open top panel trawl, and it consistently retained fewer redfish across all size classes. Underwater video footage revealed that redfish actively swam out of the BRD, leveraging turbulent water behind the Nordmøre-grid. The experimental trawl also introduced minor length-dependent selectivity for shrimp, but maintained similar size frequency distributions and catch rates, showing a non-significant 4.7 % increase in shrimp retention. This study underscores the potential of simple, low-cost behavioural BRDs to address operational challenges in Canadian northern shrimp fisheries.