on 16 Jan 2023
Conservation scientist Jesse Senko reveal how decorating nets with simple green LED lights can dramatically reduce the unplanned capture of vulnerable species
Gillnets are one of the most extensively used pieces of fishing gear in coastal regions throughout the world’s oceans. These nets are hung in vertical panels, with floats at the top and weights at the bottom. They are designed to allow the head of targeted fish to pass through, but not their body. As a result, fish become trapped by their gills.
A fisher’s dream, gillnets catch large numbers of fish very efficiently – so efficiently that their use is monitored by enforcement agencies worldwide.
But this efficiency can have a disastrous side-effect for other marine animals that the fishers are not targeting – a segment known as bycatch. While gillnets are adjusted in size and depth to try to reduce bycatch, they are nevertheless associated with declines in endangered species, including sharks, sea turtles, sea birds, non-marketable juvenile target fish and marine mammals, which get caught up in the nets. These animals are often hauled in dead or injured and simply dumped overboard.
Other issues come from lost gillnets, which impact coastal communities, and the weighted nets causing damage to underwater habitats such as coral reefs.
“Anywhere you have a coastal region, you almost certainly have gillnets,” says Jesse Senko, conservation scientist and assistant research professor at Arizona State University, USA. And, because these nets are catching pretty much everything that comes past them, he says, gillnets are a massive issue for marine conservation worldwide.
The use of large ‘drift’ gillnets longer than 2.5 kilometres on the high seas was banned by the United Nations in 1991, but there are serious ongoing violations. While a handful of jurisdictions including Belize and some US states have taken steps to ban or heavily regulate gillnetting, it is widely used by commercial fisheries globally.
In June 2021, a Singapore marine biologist discovered an abandoned gillnet on the island of Pulau Semakau that had claimed the lives of at least 12 young black-tipped reef sharks.
Images posted on Instagram by biologist Dr Neo Mei Lin showed the sharks and other creatures such as crabs entangled in the mesh.
The month prior, Singapore’s Straits Times had reported that a critically endangered hawksbill turtle was found dead in a gillnet off Pulau Hantu. It was so tightly bound that the man who freed the carcass found its head severed from its body.
In recent years, Senko and his team at Arizona State have been researching ways to modify gillnets so they can still catch target fish while reducing the devastating bycatch of other species.
And, in a paper published in Current Biology earlier this year, Senko details a solution that is surprisingly simple and incredibly effective.
“Over the past decade, illuminating gillnets with LED lights has emerged as an effective tool to reduce bycatch of endangered sea turtles in coastal gillnet fisheries,” Senko explains. “However, the effects of net illumination on other vulnerable species, total fisheries bycatch, and efficiency of fishery operations have never been tested.”
It’s already known that adding green lights to gillnets can effectively prevent sea turtles from getting caught in them. The reason behind this effect is still unclear, but researchers have hypothesised that the light repels them as it’s perceived as an annoyance.
“Gillnets are ubiquitous because they are inexpensive and catch everything that passes them” – Hoyt Peckham, Wildlife Conservation Society
Green light may be particularly effective because many marine animals have evolved to see green particularly well, and it transmits well in water. In lighting, it’s also energy-efficient relative to other colours.
But Senko wanted to look harder at this phenomenon and investigate the impact that gillnet lights have on marine animals besides turtles. In the study, Senko led a collaboration between Arizona State University and NOAA Fisheries’ Pacific Islands Fisheries Science Center, Mexico’s National Fisheries and Aquaculture Institute, and Stanford’s Center for Ocean Solutions.
The researchers attached green LED lights every 10 metres on gillnets along the Pacific coast of Baja California Sur, Mexico. Blinking like an airport landing strip, these nets were left out in a turtle-rich area at night time, and their haul was compared to light-free nets.
The incredible results found that illuminated fishing nets reduced the average total bycatch by 63 per cent, including a 95 per cent reduction in sharks, skates, and rays, an 81 per cent reduction in Humboldt squid, and a 48 per cent reduction in unwanted finfish, while maintaining catch rates and market value of target fish species the fishers were targeting.
“These results demonstrate that the benefits of illuminated nets extend well beyond sea turtles and have the potential to save countless animals, including other endangered and protected species, which would normally be tossed back dead or injured”, says Senko. “While previous studies of net illumination have focused on sea turtles, we were surprised to find that the illuminated nets effectively eliminated bycatch of sharks, skates, and rays, an imperilled group of animals that have declined globally due to bycatch and illegal fishing. Our findings show that this emerging technology could play an important role in their recovery.”
Moreover, the illuminated nets reduced the average time it took fishers to retrieve and disentangle the nets by 57 per cent, as the nets were less weighed down with unwanted bycatch.
“This likely occurred from fishers needing to remove fewer entangled animals in the illuminated nets, which included considerably fewer turtles, sharks, skates, rays, squid, and small finfish, which can be time-consuming, difficult, and even dangerous to remove,” says Senko “In practical terms, this means that fishers can save an average of 55 to 71 minutes per trip when fishing with illuminated nets, which can also help improve the quality of their fish products since they lack the proper space and capital to ice their catch at sea.”
These findings are particularly exciting for several reasons. First, the work offers a practical solution to increase gillnets’ selectivity and avoid bycatch, while not impacting the overall commercial yield that fishers rely on. Second, it creates a simple and affordable solution that can be implemented at scale worldwide with minimal expense or specialist equipment required.
Senko explains that the lights his team tested are ‘basic LED lights’, with two LEDs on the bulb. While they are powered by AA batteries, which would need to be replaced every few weeks at a recurring cost, Senko is working with a team of engineers to develop a robust solar-powered light that doubles as a floating buoy on the net.
This version of the light can stay lit for around a week with only 30 minutes of sunlight. Then, they are pulled up with the nets and recharge themselves on deck. This is vastly preferable to commercial plastic glowsticks, which are widely used by commercial fishers but are usually thrown away into the ocean after one night’s use.
Senko and co-author John Wang say they are excited for the next steps associated with this research and are currently testing new lighted net technology in coastal gillnet and pound-net fisheries in Mexico, Trinidad and Tobago, North Carolina, the Philippines and Indonesia.
“Making life easier for fishers by reducing the amount of time untangling bycatch is equally essential as reducing the bycatch biomass in nets,” says Wang, a fisheries ecologist at NOAA Fisheries’ Pacific Islands Fisheries Science Centre in Honolulu. “It is important for fishers to know that there are tangible benefits for them. This is critical for the adoption of such technologies by the fishing industry.”
The team also intends to research whether different colours and wavelengths could be more effective, how hanging them at different depths might impact bycatch, and if there’s any benefit in adding acoustic devices.
“Gillnets are ubiquitous because they are inexpensive and catch everything that passes them,” says Hoyt Peckham, a co-author of the study and the director of small-scale fisheries at the Wildlife Conservation Society. “This work is exciting because it provides a practical solution increasing gillnets’ selectivity and avoiding their bycatch. Emerging technologies should help us incorporate this kind of lighting into gillnet materials so that adopting this solution will become a no-brainer for fishers.”
Follow Jesse Senko on Twitter @jesseSenko