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

Abstract

Light-emitting diodes (LEDs) have been tested in trawl fisheries to reduce the bycatch of unwanted species through behavioural stimulation. Previous studies used LED lights to either highlight escaping routes or increase the contact rate with square-mesh panels. However, phototactic responses (moving towards or away from light sources) to LED lights could also be exploited to separate species during the catching process. We investigated if either positive or negative phototaxis can be used to improve fish vertical separation from Nephrops (Nephrops norvegicus) in the aft section of a horizontally separated trawl codend. The aim was to increase the proportion of fish entering the upper compartment. We conducted two different experiments in front of the separation into compartments, inserting green LED lights in the upper and lower netting panel, respectively. Species vertical separation was analysed and compared in two identical trawls towed in parallel, one equipped with lights and one without. We obtained significant changes in vertical separation, but no clear species-specific phototactic response was identified. Neither of the light positions improved fish separation from Nephrops. However, the potential of LED lights as behavioural stimulators is confirmed, and a more mechanistic understanding of light and fish vision may improve the results of future applications.

The effects of different artificial light wavelengths on some behavioural features of juvenile pelagic Atlantic horse mackerel, Trachurus trachurus (Actinopterygii: Perciformes: Carangidae)

“…Consequently, the use of artificial light device with such specific wavelength(s) could play key role essentially to mitigate the catch of such fish juveniles. Recent workers (Hannah et al 2015, Larsen et al 2017, Melli et al 2018) have shown artificial lights as very capable of reducing bycatch during commercial fisheries activities. In this context, it is very pertinent that workers in this specialist endeavour continue to improve their knowledge about behavioural responses of fish species toward artificial light wavelengths.…”

Predicting optimal combinations of by‐catch reduction devices in trawl gears: A meta‐analytical approach

“…towing speed) and fishing area. Figure illustrates the BRDs designs: a counter‐herding device (Melli, Karlsen, et al, ), a modification of the upper netting panel in the trawl body (Krag, Herrmann, & Karlsen, ), a horizontally divided trawl codend (Melli, Krag, Herrmann, & Karlsen, , ); a 90 mm diamond mesh codend with a 120 mm square mesh panel (SMP; Krag et al, ); and a 120 mm diamond mesh codend with a 180 mm SMP (Krag, Herrmann, Karlsen, & Mieske, ). Each of these BRDs was effective on at least one of the by‐catch species analysed, without completely excluding all commercial fish from the catch (like a grid would; Frandsen et al, ).…”

“…Schematic drawings of the BRDs included in the study. (a) Counter‐herding device from Melli, Karlsen, et al (); (b) large meshes in the upper netting of the trawl body from Krag et al, (); (c) horizontally divided trawl codend from Melli, Krag, et al (); (d) C0: 90 mm diamond codend from Krag et al, (); C1: 120 mm diamond codend from Krag et al, (); C2: 90 mm diamond codend with 120 mm SMP from Krag et al, (); C3: 120 mm diamond codend with 180 mm SMP from Krag et al, ()…”

“…If on one hand, this is the result of the higher density of undersized individuals in the population scenario; on the other hand, it can highlight that the BRDs included in the combination were less effective in improving the selectivity in proximity of the MCRS. For example, with the combination H1B0E1C0C1, cod below 30 cm are not counter‐herded and enter more frequently the lower compartment; thus, they are less likely to encounter the 120 mm mesh size of the upper codend (Melli, Karlsen, et al, ; Melli, Krag, et al, ). However, a high proportion of undersized individuals can also imply that the combination of BRDs has a length‐dependent efficiency, that is it is more effective in reducing the catch of larger individuals (e.g.…”

Size selectivity and length-dependent escape behaviour of haddock in a sorting device combining a grid and a square mesh panel

“…However, several studies in the literature have documented that haddock of different sizes may exhibit different behaviour in a trawl (Grimaldo et al, 2018;Melli et al 2017Melli et al , 2018. Therefore, it is relevant to investigate if a modelling approach that avoids the assumption of length independency on the behavioural aspect can improve the modelling of size selectivity processes for haddock in relation to grids and square mesh panels in trawls.…”