Fishing nets illuminated with green LED lights can prevent unwanted marine animals from getting stuck, saving fisheries time and stopping vulnerable animals from dying or getting injured, new research suggests.
In a study published in Current Biology, researchers found that lighted gillnets had no significant impact on the amount of targeted fish caught, yet they reduced total biomass of unwanted catch, or bycatch, by 63 percent. This improvement included a 95 percent decrease in sharks, skates and rays, an 81 percent reduction in Humboldt squid and a 48 percent reduction in finfish. The lights also reduced the average time to retrieve and disentangle nets in half.
“We were stunned with our findings,” says Jesse Senko, lead author of the study and a marine conservation biologist at Arizona State University, in a Reuters video. “We assume that it’s probably some type of warning or deterrent.”
The researchers partnered with local fishers operating off the coast of Baja California Sur, Mexico, and attached LED lights in 33-foot intervals along a gillnet, or a wall of netting that floats vertically in the water, per the study. The lights were powered by batteries that last about three to four weeks, Senko tells NPR’s Scott Simon, though they also developed solar-powered lights that can last several years.
As fish swim into gillnets, their heads can pass through the structure's holes, but their bodies can’t. They get stuck and try to free themselves, but the netting gets caught in their gills, and they become more entangled.
“Gillnets are ubiquitous because they are inexpensive and catch everything that passes them,” Hoyt Peckham, a co-author on the study and director of small-scale fisheries at the Wildlife Conservation Society, says in a statement. “This work is exciting because it provides a practical solution increasing gillnets' selectivity and avoiding their bycatch.”
Scientists estimated that 40 percent or 38.5 million tons of annual global marine catch is bycatch, according to a 2009 study. Fishers often dump the unwanted marine animals—sometimes dead or injured species—back into the ocean after they’re caught.
The practice is “driving a lot of species toward extinction," Michael Osmond, a senior program manager for the World Wildlife Fund’s Oceans Team, who was not involved in the study, says to Reuters’ Vanessa Johnston. But he tells the publication that the LED technology is promising.
Green lighted nets were originally created to reduce sea turtle bycatch, write the authors. A 2016 study found that LED nets could reduce sea turtle deaths by 64 percent. Until now, no study had looked at other vulnerable species or total bycatch with lighted nets, per a statement. Few other solutions have been desirable for both fishers and protected species.
“Bycatch of protected marine megafauna has led to fisheries regulations (e.g., closures, gear switches, and buyouts) that have incurred substantial socioeconomic costs on coastal communities,” the study states. “In this particular gillnet fishery, high bycatch of loggerhead turtles resulted in a fishery closure that eliminated the seasonal income of thousands of fishers.”
Senko tells NPR his team took an approach that would be beneficial to the fish and fishers.
“We're always looking for those win-win opportunities,” he says on NPR. “Traditionally, a lot of conservation and management approaches have basically just said, shut them down—shut all gillnet fisheries down. We've taken basically the opposite approach. We've basically said, how can we make this fishing gear more selective?”