The influence of continuous lines of light on the height at which fish enter demersal trawls

Abstract Fishing trials were conducted to investigate the effect of continuous lines of light on the height at which fish enter demersal trawls. A two-level trawl, with a horizontal separator panel that either directs fish to go above the panel to one codend or to go below it to another, was fished. A side-emitting fibre optic cable, illuminated by a light emitting diode (LED), was used to provide a continuous distribution of light on the leading edge of the separator panel and on the fishing line. During autumn daytime trials the illuminated cable only influenced common dab ( Limanda limanda ). The panel height was also varied during these trials and more lemon sole ( Microstomus kitt ), plaice, long rough dab ( Hippoglossoides platessoides ), common dab and gurnards entered the trawl above the panel when the height of its centre section was constrained to 20 cm above the fishing line. During trials held at night, in spring, the illuminated cable significantly reduced the proportion of haddock ( Melanogrammus aeglefinus ), whiting ( Merlangius merlangus ), plaice ( Pleuronectes platessa ), common dab and gurnards ( Eutrigla gurnardus and Chelidonichthys cuculus ) that swim over the panel. It did not matter whether the illuminated line was attached to the leading edge of the separator panel or to the fishing line as there was no difference in how fish entered the gear between these cases. The results demonstrate how illuminated cables can be used to modify the height at which fish enter demersal trawls, direct them to different parts of the fishing gear and potentially improve the selective performance of trawl gears. They highlight that response to the panel will be species specific and may have seasonal and environmental dependencies.