A game of two halves: Bycatch reduction in Nephrops mixed fisheries

Abstract

Trawlers that target Nephrops norvegicus and a range of demersal fish species need gear options to reduce bycatch and address European Union landing obligation requirements. We demonstrated how this can be achieved by using inclined panels to separate fish species into an upper codend with 90 mm T90-mesh, and Nephrops norvegicus into a lower codend with 80 mm diamond-mesh. A nested mixed effects model was developed to compare proportional catch at length of key species retained in test or control trawls, and based on this, the conditional probability of retention in the upper and lower test trawl codends. Haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus) < minimum conservation reference size (MCRS) were significantly reduced, while haddock ≥ MCRS, Nephrops, cod (Gadus morhua), monkfish (Lophius piscatorius), and commercial flatfish catches were generally maintained in the test trawl. Model outputs demonstrated effective separation of Nephrops into the lower codend, and size dependent separation of haddock and whiting into the upper codend. Strong performance of this catch separation device facilitates alternative selectivity measures depending on landing obligation requirements. Additional benefits such as improved catch quality and reduced catch sorting times, but also the need for further incentives to encourage industry uptake are discussed.