These simple green lights could save sharks and turtles from fishing nets | Science

An inky, tentacled squid stuck in a net can be a messy problem for a fisher. And for a loggerhead turtle or a diamond stingray, getting tangled in a net often means death. Now, new research offers hope: It shows that affixing green light-emitting diode (LED) lights to fishing nets significantly reduces the catch of nontargeted animals, such as sharks and squids, without affecting the quality and quantity of desired fish such as grouper and halibut.

“This is an excellent study that shows a reduction in bycatch of multiple species and doesn’t have a negative impact on the bottom line,” says Rebecca Lewison, a conservation ecologist at San Diego State University who was not involved with the research.

Many coastal fishers use gillnets, which hang in the water like chain-link fences, to bring in their catches. The nets—which can drift for hours or days—don’t discriminate between desirable and undesirable species, which are often tossed overboard with fatal injuries. This “bycatch” contributes significantly to the global declines of species including dolphins and sea turtles, and it slows down fishers’ daily operations.

National Oceanic and Atmospheric Administration marine ecologist John Wang and his colleagues previously devised illuminated nets to address turtle bycatch. Turtles are particularly good at seeing green light, and when the researchers found in 2016 that the lit nets cut back on turtle bycatch by 64%, they thought other marine animals might see the same benefit.

The team partnered with small-scale grouper and halibut fishers in the waters off the coast of Baja California in Mexico because of the plentiful turtles and other large marine animals there, says Jesse Senko, a conservation ecologist at Arizona State University, Tempe, and lead author of the new paper. The researchers deployed 28 pairs of nets; one net in each pair was affixed with LED lights in 10-meter increments. Then, the researchers weighed and identified each critter that was snared overnight.

The lit nets brought in 63% less bycatch, including 51% fewer turtles and 81% fewer squid, than the dark nets, the researchers report today in Current Biology. The most “gratifying” result, Lewison says, was with elasmobranchs, the group that includes sharks and rays. In the Gulf of California, she says, shark bycatch is “a huge issue.” In the new study, it went down by a whopping 95%.

Researchers are still investigating why some animals seem to avoid the lights better than others. Elasmobranchs have sophisticated eyesight, and Humboldt squids have large eyeballs, so those animals might easily spot the green radiance, the researchers say. But it’s probably too simple to say the target fish simply can’t see the lights as well as the other animals do, Wang says.

Meanwhile, just as many of the target fish were caught as before, but fishers spent only half the time hauling in and disentangling the nets. The major drawback, Senko says, is that it costs up to $140 to equip a net with lights, which is more than some fishers can afford. The researchers are now testing solar-powered lights that last longer than battery-powered ones. They’re also looking into whether fewer lights per net can produce the same results in Baja California and in fishing grounds in Indonesia and the Caribbean. The fishers’ needs are important in these projects, Lewison says. “They’re the folks who are using these nets every day.”