One of the many threats facing sea turtles, all species of which are categorized as threatened, is net fishing. Turtles can unwittingly become scooped up in fishing nets as bycatch.
Now, a team of scientists at the University of Exeter has discovered that attaching green LED lights to nets used by small-scale fisherman can reduce the number of green sea turtle deaths by 64 percent. The lights don’t seem to affect the number of fish caught, which means the intervention is less likely to be rejected by fisheries.
“Small-scale net fisheries are one of the most common fishing methods globally, and sea turtle bycatch in net fisheries is very high,” says Jeffrey Mangel, a Darwin Initiative research fellow based in Peru. “And yet very few solutions have been identified that can effectively reduce turtle bycatch in these types of fisheries.”
Many of these small-scale fisheries are in the developing world, which means any solution needs to be something inexpensive and easy to implement.
“The idea of using the lights comes from asking how we can change the behavior of animals, in this case sea turtles, in ways that can reduce their interactions with fishing gear,” Mangel says. “Animal behavior is driven in part by their senses—sight, smell, hearing—so in this study we wanted to see if by adding the light to the net, we could change turtle behavior and reduce their bycatch. And that seems to be the result.”
The study took place in a working fishery in Sechura Bay in northern Peru, which is home to multiple populations of sea turtles. Peru’s gillnet fishermen are estimated to set 100,000 kilometers of net each year, unintentionally killing thousands of sea turtles. The team used 114 pairs of nets, one with LED lights every ten meters along its floatline, and one unaltered to serve as a control. The control nets caught 125 turtles while the illuminated nets caught only 62.
Prior to the Peru study, initial trials on net illumination had been conducted by John Wang and Yonat Swimmer at the National Oceanic and Atmospheric Administration. Wang and Swimmer tested illuminated nets in Baja, Mexico, though not in an active fishery known for sea turtle bycatch.
In the Peru study, each LED light cost about $2, which meant the cost of saving a turtle was about $34. The team expects this price will go down if the LED nets are used on a larger scale.
The team’s next steps, which are already underway, are to test LED lights in other kinds of net fisheries. They’ll see whether combinations of different types of nets used with different types of target catch and different species of sea turtles will be effective. They’re also testing out different colors of lights to see if particular color wavelengths are more or less effective in reducing sea turtle bycatch and reducing effects on target catch. Additionally, they’re looking to see if light-up nets might reduce the bycatch of sea birds and small cetaceans such as dolphins. The team hopes light-up nets might be useful globally as an inexpensive solution to bycatch.
“In an ideal world, net fisheries, like any other fishery, would be able to fish sustainably—both for their target catch species and for any incidental (or bycatch) species,” says Brendan Godley, a professor at the University of Exeter and a member of the team. “And in an ideal world, these fisheries would provide fishermen and fishing communities with sustainable livelihoods, that provide food and employment to these communities into the future.”