Illumination of trawl gear by mechanically stimulated bioluminescence

The role of bioluminescence stimulated by moving fishing gear was investigated using an ISIT video camera mounted inside a pelagic and demersal trawl. Data presented here show that trawling is responsible for generating bioluminescent light. In two Norwegian fjords, the mean number of bioluminescent events per metre of head rope per second were 5.14 ± 2.17 and 2.39 ± 1.0 for a pelagic trawl at not, vert, similar270 m depth and a demersal trawl at not, vert, similar500 m depth, respectively, travelling at 2–4 knots. By extrapolation of these data, thousands of point-source flashes occur over the entire mouth of a trawl every second during a tow, considerably increasing its visual presence to fish. The occurrence of stimulated bioluminescent flashes on a trawl in deep-water may provide sufficient illumination to permit herding in the absence of ambient space light. The aim of this study is to bring to the attention these preliminary observations of mechanically stimulated bioluminescence by mobile trawl gear as possible visual detection stimulus for fish and its potential to affect catch rates by altering herding, escapement and avoidance behaviour.