A field and laboratory investigation of the influence of light on the behaviour of Atlantic cod (Gadus morhua)

Enhancements to fishing gears that could increase their efficacy are becoming globally popular both in use and in research. Effective enhancements could facilitate fishing, encourage sustainability through economic incentives, and mitigate bycatch. Visually mediated behaviours can be exploited by fishers to influence the capture of target species through modifications to the light environment, such as LED lures. Atlantic cod (Gadus morhua) are a commercially harvested species adapted to a low-light environment with a narrow range of available wavelengths in the blue-green range, and devices using green light are commonly available to fishers. To test the behaviour of cod in relation to LEDs, I assessed the catch efficacy of handline gear with green LED attachments and performed experiments in an artificial setting with multiple colours of LEDs to study phototactic responses to various wavelengths of light. Catch rates of handlines did not improve with the use of LED lures. As well, no behavioural responses were observed in choice test experiments, indicating that light may not be effective for exploiting the behaviour of Atlantic cod. These findings can be applied directly to fishery and aquaculture practices and encourage further research into the role of visual ecology in the conservation of Atlantic cod.