Solutions to bycatch in fisheries have so far been technical, with selectivity devices to filter out unwanted catch – or regulatory, encompassing a range of closures and other measures to keep fishing vessels away from particular areas. The drawback is these are often expensive and require increased monitoring and enforcement.
Bycatch can also be a major problem on deck. It increases their sorting time and results in the cumbersome, time-consuming and potentially costly process of cleaning, untangling and repairing nets. Species such as sea turtles or sharks can present physical hazards and these also require careful handling –all of which can result in additional expenses, maintenance time and opportunity cost.
Researchers at Arizona State University have found another potential solution – fishing nets that glow green with LED lights. Working off the coast of Baja California in Mexico, the team compared the performance of 5000 metres of regular gill nets against 5000 metres of illuminated gear. Their work was published in the journal Current Biology.
A finding of the study is that illuminated nets had no significant impact on the amount of targeted fish caught. Jesse Senko, a marine conservation biologist at Arizona State University and lead author of the study, and his team believe that this is because bycatch species behave differently to target fish species. For example, the vision and visual capacity of fish can vary across species and life stage, which may explain why net illumination reduced finfish bycatch but not target finfish catch.
In juvenile fish, visual systems are used to perform simple tasks such as vertical migrations to avoid predators, whereas older life stages have more developed visual systems that are used for complex tasks like predation, spatial vision, navigation, reproduction and communication. Predator avoidance, or predation itself, may have also played a role in the reduced bycatch rates observed in illuminated nets.
‘As an example, large target finfish may have been attracted to the illuminated nets as a means to aid or enhance predation, resulting in smaller finfish bycatch avoiding the illuminated nets or even being preyed upon. As a consequence, behavioural avoidance or predation in the area adjacent to the illuminated nets may have contributed to the higher finfish bycatch rates observed in control nets,’ he said, commenting that bycatch is a global problem, not least in coastal gillnet fisheries of developing nations,
‘Over the past decade, net illumination has emerged as a promising tool to reduce bycatch of endangered sea turtles in coastal gillnet fisheries while maintaining target catch. However, its potential effects on total bycatch biomass, other species and fishery operations remain unknown and represent important knowledge gaps in this emerging field. Assessing these broader effects is fundamental to understanding the applicability and adoption potential of net illumination in similar coastal gillnet fisheries. This is why we conducted our study.’