Investigating fish behavioural responses to LED lights in trawls and potential applications for bycatch reduction in the Nephrops-directed fishery

33 Light Emitting Diodes (LED) have been tested in trawl fisheries to reduce the bycatch of 34 unwanted species through behavioural stimulation. Previous studies used LED lights to 35 either highlight escaping routes or increase the contact rate with square mesh panels. 36 However, phototactic responses (moving towards or away from light sources) to LED lights 37 could also be exploited to separate species during the catching process. We investigated 38 if either positive or negative phototaxis can be triggered in fish to modify their vertical 39 distribution in the aft section of a horizontally separated trawl codend. The aim was to 40 separate fish into the upper compartment and Nephrops ( Nephrops norvegicus ) into the 41 lower compartment. We conducted two different experiments in front of the separation 42 into compartments, inserting green LED lights in the upper and lower netting panel, 43 respectively. Species vertical separation was analysed and compared in two identical 44 trawls towed in parallel, one equipped with lights and one without. Significant differences 45 in species vertical distribution were observed; however, most effects resulted in increased 46 number of individuals entering the lower compartment. No clear species-specific 47 phototactic response was identified and the results highlighted the challenges of inferring 48 behavioural responses in trawls. Future steps required to improve the understanding of 49 fish reactions to artificial lights are discussed. 50