Adult sea turtles may have few natural predators — unless you factor in human beings.
One of the many threats to sea turtles, as well as dolphins, whales and sea lions, are gillnets. A gillnet is a wall of netting suspended in the water (imagine a tennis net strung along the bottom of the ocean). Fishers aim to trap fish, not other marine animals, but gillnets don’t discriminate, and those unintentionally caught animals are called bycatch.
With nearly all sea turtle species endangered, it’s become a priority for scientists and conservationists to find solutions to reduce sea turtle bycatch.
The sheer number of fishers underscores the problem: Off the coast of Indonesia, there’s an estimated 300,000 small-scale vessels that fish in those waters. In Peru, it is estimated that 100,000 kilometers of gillnet is set each year along the coast. Even in the United States, along the coast of North Carolina, fishermen are casting gillnets into the ocean and hauling back entrapped animals.
“A mind-boggling amount of fishing effort goes on in that very small interface between humanity and our oceans,” said John Wang, who leads gillnet bycatch research at the NOAA Pacific Islands Fisheries Science Center.
Scientists are turning to lights to help solve the problem.
By attaching an LED light every 10 meters on the net’s float line, turtles are able to see the gillnets more easily.
“[We’re] not scaring turtles. The lights aren’t making the turtles annoyed or anything,” Wang said. “What we’re doing is we’re increasing their awareness that something odd is going on.”
By increasing the turtles’ awareness of their immediate surroundings, they tend to avoid the nets.
Research indicates the lights are working. Illuminated gillnets have decreased sea turtle bycatch without decreasing target catches.
Studies in Mexico found green sea turtle bycatch reductions between 40 and 60%. Researchers in Indonesia showed that green, olive ridley and hawksbill sea turtle bycatch was reduced by 60% and the target catch increased. And in Peru, illuminated nets have reduced green sea turtle bycatch between 65 and 80%. Collaborators have also expanded research out to areas in Pakistan, Ecuador, Italy, Slovenia and Ghana.
“Even though mom and pop fisherman in Mexico might be fishing a kilometer to two kilometers of net, boy, there’s a lot of [people] fishing one or two kilometers,” Wang said. “And it quickly adds up to a scale that’s comparable, if not more, than some of the industrial fisheries.”
Illuminated gillnets can help these “mom and pop fishermen.” When a turtle or other animal gets tangled in the nets, fishers spend time, money and effort untangling and repairing the nets. By adding lights, an illuminated gillnet, in theory, reduces these efforts.
“That’s not to say that there isn’t a cost associated with these lights,” Wang said. Researchers are working in both developed and developing countries, so funding for these lights isn’t always easy to come by. Scientists are working with conservation groups, like WWF, along with government entities to support subsidies for lights.
For example, in Indonesia, WWF collaborated with the Ministry of Fisheries to adopt lights into its management plan. And the government is now looking at developing its own LED light industry.
“LED lights for fishing, they’re already there,” Wang said. “It’s a matter of getting the pricing down, making them more sustainable through some of the solar technology we’re working on, and creating the supply chains so that fishermen in these remote places actually have access.”
At Arizona State University, biologist Jesse Senko is working with NOAA to power lights with solar technology. And other scientists are looking at how colored lights might maximize bycatch reductions.
Beyond just sea turtles, illuminated gillnets can potentially reduce bycatch in other species like cetaceans, which include species like dolphins; and elasmobranchs, which include species like sharks and rays.
“And now you have a single tool that can be fairly influential across multiple taxa of animal,” Wang said. “That helps these small-scale fisheries become that much more sustainable for the long run, and that’s ultimately what’s important.”
Correction: A previous version of this article incorrectly stated that the whales are elasmobranchs. Additionally, Peru has an estimated that 100,000 km of gillnet is set each year, not Northern Peru. NationSwell apologizes for the errors.