Our oceans are full of sophisticated, perfect traps: Nets, hooks, fishing lines. Designed to capture animals destined for our dinner tables, they often catch other wildlife too.
This accidental harvest is known as bycatch, and every year it causes the death of millions of marine animals, including whales, dolphins, sharks, turtles, and seabirds. Nets and gear can asphyxiate animals or cause fatal injuries; even when the animals are tossed back to sea, they frequently die. Bycatch is also a dilemma for fishermen—entangled creatures can destroy equipment, costing time, money, and fisheries’ reputations.
Over the decades, conservationists, researchers, and fishermen have developed ways to minimize various kinds of bycatch in different fishing stocks around the world. But putting these solutions to work is often a challenge, and many mitigation strategies are never widely implemented.
Some approaches, however, now have a proven success rate—and more may be on the horizon. Recent research has explored nets equipped with lights; even low-tech tricks like kitting out gear with plastic water bottles show promise of reducing some kinds of bycatch while also being practical for fishermen to use.
Despite the challenges, researchers are hopeful. “There are not very many conservation issues that I’m aware of where industry and conservationists and consumers and the fishermen and the resource users all want the same thing,” says marine biologist Matthew Savoca, a research scientist at Stanford University’s Hopkins Marine Station. “Every stakeholder wants less bycatch.”
Keeping turtles out
The bycatch problem has always existed. “It’s a conflict that’s intrinsic to the whole idea of fishing,” says marine scientist Nancy Knowlton, marine biologist emerita at the Smithsonian’s National Museum of Natural History. “If you have something that’s designed to catch animals, you’re going to wind up, almost always, catching some things that you didn’t mean to catch.”
Yet mitigation measures can make a difference—and without significantly reducing the catch of the target species, says Cheng Huang, an expert in sustainability ecology at South China Normal University. Huang and colleagues recently assessed 42 different bycatch prevention measures reported in 121 case studies and found they generally do reduce bycatch of vulnerable marine species. But there isn’t a one-size-fits-all solution.
“Bycatch is a multi-species, multi-gear and multi-scale problem,” says Huang. “Expecting a single technical fix to work everywhere is unrealistic.”
Sea turtles, many species of which are endangered, are among the animals harmed by bycatch—and one of the success stories. In the 1970s, populations of the animals were threatened by shrimp fisheries in waters off the southeastern United States. Researchers started working with commercial fisheries to develop turtle excluder devices that provide an escape route for turtles and other marine animals after they’ve entered the wide mouth of trawl nets. After many iterations, and eventually regulations, the devices became widely adopted, and current designs are 97 percent effective. The devices also save fishermen time and money—preventing the loss of shrimp to fish and hungry turtles.
Yet turtles are still threatened by multiple types of fishing gear: Estimates suggest that more than 250,000 of the creatures die as bycatch each year. Gillnets, which hang like curtains in the water, or bottom longlines, which string baited hooks held in place by weights along the seafloor, can be especially dangerous for the animals.
Attaching green LED lights or UV lights to gillnets in the water seems to deter turtles from the deadly traps. In one early test of the idea, researchers compared UV-illuminated gill nets to non-illuminated gill nets in Baja California, Mexico, and found that the lighted nets reduced turtle bycatch by 40 percent.
Lighted nets have since been tested for multiple species and fisheries worldwide. A study in the waters of northern Peru’s Sechura Bay, for example, showed a turtle bycatch reduction of more than 60 percent thanks to LED-illuminated nets. But they have yet to be implemented in fisheries on a large scale. Barriers include cost and the perception that lights might reduce target fish catch, says marine conservation scientist Jesse Senko of Arizona State University. Part of the expense is batteries for the lights, which need to be replaced often.
Senko and his colleagues, after consulting with local fishers, designed solar-powered lights that regularly flash and tested the approach in a coastal gillnet fishery that catches yellowtail amberjack in the Gulf of California, Mexico. They attached lights to 28 gillnets, each paired with a gillnet with deactivated lights as controls, for 650 hours in an area known for high levels of turtle bycatch. The nets with lights reduced expected turtle bycatch by 63 percent while maintaining target fish catch, the researchers reported in Conservation Letters in October 2025.
The lights didn’t only reduce power consumption, they also worked as buoys, making them easily integrated into the fishing gear. This is crucial for adoption of new techniques, says Senko. “All of a sudden, the light was more or less part of their gear,” he says. “It wasn’t some foreign thing on their net. It was just another buoy that happened to flash green light.”
Pingers and plastic bottles
Another bycatch prevention method that’s demonstrated some success is pingers—devices attached to the fishing gear that emit sounds that deter echolocating whales and dolphins. A field trial of the devices in three Norwegian fisheries using gillnets, for example, showed that pingers reduced bycatch of harbor porpoise by 94 percent, a team reported in Fisheries Research in 2023.
But pingers can have their downsides. An analysis of pinger effectiveness in waters off the United Kingdom, where they have been used for more than a decade, found that while they were linked to a reduction in bycatch of porpoises, they were also linked with an increase in bycatch of seals, which seem to associate the sound with a potential meal. “It’s like a dinner-bell effect,” says policy specialist Sarah Dolman of the Environmental Investigation Agency, a London-based nonprofit that campaigns for environmental issues.
Pingers that transmit at frequencies outside of pinnipeds’ hearing range and are thus considered “seal-safe” have been developed. But the devices can also be expensive, especially for artisanal fishermen, who tend to use lower-tech gear and may lack supportive government policies and investments.
Some of those small-scale fisheries may reduce bycatch of echolocating animals with a low-tech approach: fixing plastic water bottles to their nets. Detecting thin, fine nets is difficult for dolphins, porpoises, and other echolocators, but water bottles are a more easily detectable obstacle that could help them avoid the net. A preliminary study conducted in Brazil found that using plastic bottles on nets was effective at reducing the bycatch of franciscana dolphins, a threatened river dolphin species. It’s a realistic option, says Dolman, in places where fishermen don’t have the funds to buy and maintain pingers.
Practicalities, along with cost, often prevent implementation of bycatch prevention measures, even the ones that work. Many solutions that get developed and tested never end up being widespread.
“We’re very good at providing funding for scientists to conduct trials to reduce bycatch, but very rarely do those trials then continue to the whole of the fleet,” says Dolman.
For a solution to work on a large scale, a number of conditions must be met, says marine sustainability scientist Lekelia Jenkins of Arizona State University. Policies and regulations need to be in place, and they need to be enforced. And perhaps just as important, the preventive measures need to be practical for fishermen and not add extra time and money to the job. “The smaller the change, and the more it feels like their traditional fishing practices, the more likely they’re going to adopt it,” Jenkins says.
The human side of the issue also needs to be acknowledged. “Emotionally, fishermen around the world are beat up and beat down,” Jenkins says. “We say, ‘You’re the problem. You’re catching sea turtles and whales. You are the bad guy.’” Instead, fishermen should be empowered and included in the discussions and development of solutions. “The weight of saving the world’s oceans,” Jenkins says, “can’t fall solely on their shoulders.”
This story originally appeared in Knowable Magazine.
