Green Lights Could Save Birds and Turtles From Fishing Nets

Both animals were less likely to get ensnared by fishing nets that shined green light, a new study found.

Published 12 Jul 2018, 16:03 BST, Updated 5 Nov 2020, 06:04 GMT
Sea birds like this one are suspectible to getting trapped by fishing nets. A new paper ...

Sea birds like this one are suspectible to getting trapped by fishing nets. A new paper showed that cormorants are deterred when fishing nets shine green lights.

Photograph by Pierre GLEIZES, REA/Redux

Scientists are hoping green light could offer marine animal conservationists a glimmer of hope.

A new study found that green LED lights affixed to gillnets—a type of net that hangs like a curtain in the water—reduced the number of cormorants, a type of sea bird, unintentionally snared when diving into the water for fish by 85 percent.

The method was originally developed to save sea turtles. Green became the color of choice because turtles are able to see the wavelength, but fish aren't, meaning the light can be used to shoo turtles away without jeopardising catch.

All sea turtle species are either threatened or endangered, and incidental catch by fishermen poses a threat to their existence. Previous studies by the same research group showed that the number of sea turtles accidentally caught in fishing nets dropped by 64 percent when green LEDs were in place. The new study published in the journal Open Science is giving researchers hope that more species can be saved with a low-cost tool.

114 fishing nets with LED lights at every 10 metres were deployed in studies done off the coast of Peru.

Photograph by ProDelphinus

Animal rights groups, however, remain sceptical that the method won't prevent further harm to oceanic animals.

Testing the Green Light

Sea creatures that get dredged up onto fishing boats unintentionally are referred to as bycatch. It's an unintended consequence both fishers and conservationists try to avoid. Everything from dolphins and whales to turtles and sharks end up as bycatch every year. For species whose population numbers are already low, bycatch only worsens their dilemma.

Fishing companies also have an incentive to reduce bycatch because unintentionally caught animals can damage nets.

To test how effective a light could be, University of Exeter biologist Jeffrey Mangel worked with Peruvian conservation group Pro Delphinus to study 114 nets—averaging about 500 metres in length—off the coast of Constante, Peru.

“We tested in this particular place because it has a high interaction rate with sea turtles,” says Mangel. Acoustic pingers have been tested on nets to deter dolphins and whales with some success. The underwater noises are thought to deter cetaceans because the animals use acoustics to communicate. An effective method to deter birds and sea turtles has thus far been elusive.

And scientists aren't exactly sure why the green light works.

“What we know is it seems to work and now the question is 'why does it work'?” says Mangel.

NOAA ecologist John Wang looked at how sea turtles interact with light in 2007 and concluded that, when the turtles were placed in a dark tank, light attracted them.

Wang, who was also an author on this paper, says the reason turtles were attracted to light then but averse to it now comes down to, “how an animal responds to a sensory cue in a specific context.”

In the case of a gillnet, a turtle or bird might simply be able to evade capture because it sees a barrier in the water.

The theory that context is key for deploying LED lights might also explain why the method doesn't work on longlines, a type of fishing method in which bait is singularly attached to one long, single line of fishing wire. Many fishers attach glow sticks near the bait to attract catch.

Can Everyone Use It?

In Peru, gillnets are the most common fishing method used by small-scale fishing operations, and Mangel hopes integrating lights into fishing techniques will help find a happy middle ground between those who live off the fish in the water, and those who want marine animals to keep living.

“These communities are fishing communities, and we're trying to find solutions to allow fisherman to keep fishing,” says Mangel.

“To us, it does seem scalable. If we can get the cost of lights down to a couple of dollars per light, you're looking at something you can conceivably implement in small-scale settings,” adds Mangel.

"The potential benefits of this illuminated gillnet technology to reduce bycatch could also create opportunities for more sustainable fisheries, given the extent of fishing activities with gillnets along the Peruvian coast," said Juan Carlos Riveros, Oceana Peru's science director, in a statement. However, he called for more research studying the light's full impacts.

"It's important to further investigate the impacts of using this technology in different scales before widespread implementation," he says.

While often supportive of any method that reduces the killing of wildlife, some animal rights groups are taking hardline approaches to gillnets.

“Generally, gillnets are curtains of death for target and non-target species alike,” says Todd Steiner, executive director of the Turtle Island Restoration Network over email. His concerns with ideas like LED lights are that an attempt to save one species might exacerbate the take of another species.

Kenny Torilla from Mercy for Animals also echoed Steiner's stance, adding that his organization supports cutting fish from one's diet.

In future studies, Mangel and Wang plan to continue researching how low-cost methods like LED lights can be used to deter other marine species like dolphins, whales, and porpoises.

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