New research has shown that simply adding LEDs to the gillnets of small scale fisheries can drastically reduce number of dolphins and turtles that get caught as unintentional bycatch.

It’s that time of year again where just about everything in sight is covered with thousands and thousands of twinkling lights. But this year a new study, from the University of Exeter and Peruvian NGO ProDelphinus, has been getting marine conservationists in the festive spirit by adding similar lights to fishing gear. By attaching LEDs to the gillnets of small scale fisheries across Peru the researchers were able to seriously reduce the number of dolphins and turtles that were accidentally caught by fishermen, without reducing the number of fish they caught. This illuminating idea is not just effective but also simple and relatively cheap, and it could also be used in the thousands of similar small scale fisheries across the world.

What are gillnets?

Gillnets are effectively big walls of net that are designed to trap fish by their gills as they attempt to swim through them. Gillnets can either be fixed to the seafloor or released off fishing vessels to drift through the sea, but regardless they are one of the main methods of fishing in small scale fisheries across the globe. Unfortunately these massive walls of netting don’t discriminate between fish and anything else that tries to swim through them. It is for that reason that they are responsible for the unintentional bycatch of turtles, dolphins, sharks, seabirds and just about any other non-target species they come across. The number of animals that die as a result is a leading cause of population decline in many of these species.

An illuminating idea

Despite the destructive impact of gillnets the number of solutions to reduce their bycatch rates have been very low. However recent studies into using sensory cues such as sound and light to reduce bycatch have shown some signs of promise. Following on from this researchers from the University of Exeter decided to trial using LEDs to light up gillnets. Lead researcher Alessandra Bielli said in a press release that “sensory cues – in this case LED lights – are one way we might alert such species to the presence of fishing gear in the water”. To do this they teamed up with Peruvian NGO ProDelphinus along with small scale gillnet fisheries from the ports of San Jose, Salaverry and Ancon.

Between 2015 and 2018 the team attached LEDs to the gillnets used in 864 fishing trips from the three locations. The lights were attached every 10 metres along the net’s floatation line and used compared to a control net with no lights. In the new paper released by the researchers in the Biological Conservation journal we can see that those lights had a big impact. It showed that LEDs reduced the bycatch rate of sea turtles by more than 70%, and that of small cetaceans (including dolphins and porpoises) by more than 66%. The main species that benefited were green turtles, long-beaked common dolphins and dusky dolphins, whilst Olive Ridley turtles and Burmeister’s porpoises were also helped. Other studies have also shown that similar LED set-ups can reduce the rate of seabird bycatch by as much as 85%. So whilst this method is not perfect it is easily one of the most effective solutions for gillnets ever trialled.

Simple but effective

Exeter PhD graduate Dr Jeffrey Mangel, who now works with ProDelphinus, says that“The dramatic reduction in bycatch of sea turtles and cetaceans in illuminated nets shows how this simple, relatively low-cost technique could help these species and allow fishers to fish more sustainably. Given the success we have had, we hope other fisheries with bycatch problems will also try illuminating their fishing nets”. There is still some work to do, more types and combinations of lights need to be tested to see if the method can be improved. But hopefully it is not too long before gillnets everywhere are lit up to reduce bycatch which, could seriously reduce the pressure on some of these already struggling marine creatures.

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