Lighten up: using artificial light to improve the capture efficiency of fishing gears

Nguyen, Khanh Q. (2019) Lighten up: using artificial light to improve the capture efficiency of fishing gears. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Snow crab (Chionoecetes opilio) is an important commercial shellfish and one of the most valuable fisheries in eastern Canada. The Newfoundland and Labrador snow crab fishery has been the world’s largest for the past two decades. Total landings grew substantially between the 1980s and 1990s, but more recently, the industry has been faced with new challenges including decreases in stock abundance (i.e., poor pre-recruitment), changes in environmental condition (i.e., warming ocean water temperatures), conflicts with shrimp trawlers, effects of seismic exploration, and increases in operating costs. Maintaining the economic viability of small fishing businesses in the presence of these new stressors can be a challenge. In output-controlled fisheries such as snow crab, improving the catch rate of existing traps is an effective method of improving the financial viability of small fishing businesses. In this thesis, I conducted a comprehensive examination of the behaviour of snow crab in response to artificial light (i.e., Light-Emitting Diode (LED) lights and luminescent netting), including laboratory and field experiments, to address the primary goal of improving the catch rate of small conical traps commonly used for catching snow crab in the North Atlantic Ocean. First, I conducted a literature review regarding the use of artificial light in commercial industrialized fisheries. The review provides valuable knowledge and reference for scientists, managers, and fishermen on animal behaviour in response to artificial light. It also addresses the trade-off between positive effects such as increased catch rate and reduced bycatch with negative effects such as the production of increased plastic, ocean litter, and greenhouse gas emission. Second, I conducted 7 experiments to investigate the behaviour of snow crab in response to artificial light, including 2 laboratory studies and 5 field studies, to address the primary goal of improving the catch rates of snow crab traps. Results from the laboratory experiments indicated that snow crab responded differently to different light colours. Field experiments in 2016 demonstrated that equipping baited traps with small low-powered LED lights increased the Catch Per Unit Effort (CPUE; number of crab per pot) of the traps (i.e., 77% and 47% for white and purple LED lights, respectively). Next, I examined the effect of installing underwater LED lights in different locations and orientations inside baited traps targeting snow crab off the coast of Newfoundland and Labrador, Canada. Results from this field experiment in 2017 revealed that the location and orientation of lights does not appear to be important. Next, I conducted a comparative fishing study onboard a large offshore fishing vessel targeting snow crab in the Barents Sea, off the coast of Norway. Results revealed that equipping baited traps with purple lights increased the CPUE by 11.6%, although the results varied with the density of crab. Finally, I examined the potential application of luminescent netting as a source of artificial light to determine whether it could be used to improve the CPUE of traps. A benchtop laboratory experiment was conducted to measure the duration of luminescence using time-lapse photography. I found that luminescent netting can be activated to emit light and that the resulting intensity and duration of luminescence emitted over time, depends on the initial duration of UV exposure and the source of light. A follow-up field experiment in 2018 showed that luminescent traps significantly increased the catch rate of snow crab compared to traditional traps. Overall, the results of my PhD research demonstrate that artificial light can improve the catch rates of snow crab traps, with examples from different light sources (i.e., LED light, luminescent netting) and locations (Barents Sea, Newfoundland and Labrador). These results suggest that the application of artificial light in commercial snow crab fisheries could improve the financial viability of fishing enterprises.

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