Researchers from the University of Exeter and the Peruvian conservation organization ProDelphinus have found that installing LED lights on top of floating gillnets reduces the accidental catch of unwanted species dramatically. A study from three Peruvian ports between 2015 and 2018 shows that the lights cut the bycatch of sea turtles by 70 percent and dolphins and porpoises by 66 percent.
Gillnets have been standard equipment for fishermen all over the world since ancient times. Designed to catch fish by their gills (hence the name), gillnets are made of weighted vertical panels of netting that hang by vertical lines attached to floats, so the whole thing hangs down like a curtain. When the fish swim into the mesh, their gills get tangled as they try to pull back and they're trapped.
For such an old technology, gillnets are remarkably efficient – so much so that their use is heavily regulated under national and international law to prevent overfishing and the catching of unwanted species. Fortunately, by tweaking the various elements of the nets, they can be made highly selective, but problems still remain.
One big problem is that gillnets can not only catch fish, but also seabirds, sea turtles, and small cetaceans. According to the Exeter team, LED lights have already proven successful in cutting seabird catches by 85 percent, so why not try them on other species?
"Gillnet fisheries often have high bycatch rates of threatened marine species such as sea turtles, whales, dolphins, and seabirds,” says research lead Alessandra Bielli from the Centre for Ecology and Conservation at Exeter’s Penryn Campus in Cornwall. “This could lead to declines in the populations of these non-target species – yet few solutions to reduce gillnet bycatch have been developed. Sensory cues – in this case, LED lights – are one way we might alert such species to the presence of fishing gear in the water."
For the test, the float lines of 864 gillnets were equipped with LED lights every 10 m (33 ft) and each was paired with an unlighted net as a control. The researchers found that the control nets caught green turtles, loggerhead turtles, olive ridley turtles, long-beaked common dolphins, dusky dolphins, and Burmeister’s porpoises, but the LED nets had much lower bycatch numbers.
"This work has further shown the usefulness of lights on nets to save wildlife. We now need lights that are ever more robust and affordable," says Professor Brendan Godley, of the University of Exeter.
The research was published in Biological Conservation.
Source: University of Exeter