Tests of artificial light for bycatch reduction in an ocean shrimp (Pandalus jordani) trawl: Strong but opposite effects at the footrope and near the bycatch reduction device

We investigated how the addition of artificial light in the vicinity of the rigid-grate bycatch reduction device (BRD) and along the fishing line of an ocean shrimp (Pandalus jordani) trawl altered fish bycatch and ocean shrimp catch. In separate trials using double-rigged shrimp nets, with one net incorporating artificial lights and the other serving as a control, we 1) attached one to four Lindgren-Pitman Electralume® LED lights (colors green or blue) in locations around the rigid-grate BRD, and 2) attached 10 green lights along the trawl fishing line. Both experiments were conducted with rigid-grate BRDs with 19.1 mm bar spacing installed in each net. Contrary to expectations, in 12 paired hauls the addition of artificial light around the rigid-grate increased the bycatch of eulachon (Thaleichthys pacificus), a threatened anadromous smelt species, by 104% (all by weight, P = 0.0005) and slender sole (Lyopsetta exilis) by 77% (P = 0.0082), with no effect on ocean shrimp catch or bycatch of other fishes (P > 0.05). In 42 paired hauls, the addition of 10 LED lights along the fishing line dramatically reduced the bycatch of a wide variety of fishes with no effect on ocean shrimp catch (P > 0.05). Bycatch of eulachon was reduced by 91% (P = 0.0001). Bycatch of slender sole and other small flatfishes were each reduced by 69% (P < 0.0005). Bycatch of darkblotched rockfish (Sebastes crameri), a commercially important but depressed rockfish species, was reduced by 82% (P = 0.0001) while the bycatch of other juvenile rockfish (Sebastes spp.) was reduced by 56% (P = 0.0001). How the addition of artificial light is causing these changes in fish behavior and bycatch reduction is not known. However, in both experiments the addition of artificial light appears to have greatly increased the passage of fishes through restricted spaces (between BRD bars and the open space between trawl fishing line and groundline) that they typically would not pass through as readily under normal seafloor ambient light conditions.