Whales, dolphins and porpoises are protected from hunting in most places these days. But that doesn’t mean they’re safe from fishing.
Accidental entanglement and drowning, often called bycatch, is one of the greatest threats to cetaceans. The overwhelming majority of those incidents were tied to gillnets, curtains of virtually invisible nylon mesh dangled in the water, indiscriminately trapping anything that swims into them.
The carnage is worldwide. In the Indian Ocean, an estimated 4.1 million small cetaceans such as dolphins died between 1950 and 2018 in gillnets targeting tuna. Gillnets have pushed Mexico’s vaquita porpoise to the brink of extinction. In U.S. waters, the nets claimed more than 6,000 marine mammals every year in the 1990s.
But for at least some gillnets, the solution might be easily at hand in the nearest trash can. Plastic drink bottles tethered to drift nets cut bycatch of an endangered South American dolphin by nearly 90% without affecting the overall amount of fish caught, according to new research in Marine Mammal Science.
“This is a good news story and something that we strive for—a simple solution that benefits both dolphins and the fishers who use the gear,” said Per Berggren, a marine conservation scientist at the United Kingdom’s Newcastle University who developed the idea of using the bottles. “Attaching plastic bottles to fishing nets can reduce dolphin bycatch globally and is something that every fisher can afford.”
The arrangement is remarkably low-tech, taking advantage of the acoustic properties of air-filled bottles and the hunting strategies of dolphins. Slender-snouted franciscana dolphins, which grow to a little less than 2 meters, pursue fish close to shore in Brazil, Uruguay and Argentina. That puts them in direct conflict with small scale fishers, who sink their nets to the seafloor.
The dolphins use echolocation to survey their surroundings, emitting a series of clicks and then interpreting the sounds reflected back to them. The air-filled bottles act a bit like mirrors, reflecting the clicks better than the fine mesh of the nets.
The researchers attached the small bottles every 130 meters along the upper edge of nets that totaled 3 kilometers in length, like wide-spaced Christmas lights. Working with fishers in southern Brazil, between 2020 and 2025 they tracked what came up in the bottle-festooned nets compared to regular nets.
The results showed a dramatic 88% fewer dolphins caught in the bottle-topped nets when adjusted for the total amount of time each set of nets were in the water. In the modified nets, just one franciscana dolphin was caught, compared to eight franciscana dolphins and two bottlenose dolphins in the standard nets.
At the same time, there was no significant change in the number of fish caught in the nets, meaning there was little downside to the bottles.
“This is genuinely recycling that rescues dolphins,” said Berggren.
That doesn’t mean this is a silver bullet for all bycatch problems. Similar experiments in Zanzibar and Peru with gillnets that float near the surface didn’t produce the same benefits, according to a companion paper in Fisheries Research. Berggren suspects that’s because the surface water is a “noisier” environment, obscuring the presence of the bottles.
There are fancier devices that might overcome some of the weaknesses of the plastic bottles. For instance, there are electronic devices that can be attached to nets that emit a “ping.” But the researchers note that the cost of buying and maintaining them might be deterring small-scale local fishers from adopting them.
Empty plastic bottles, on the other hand, are all too abundant.
Sucunza, et. al. “Evidence of Dolphin Bycatch Reduction With Upcycled Plastic Bottles Acoustic Reflectors Attached to Bottom-Set Gillnets.” Marine Mammal Science. May 18, 2026.
Berggren, et. al. “Upcycled glass and plastic bottles offer potential low-cost mitigation to megafauna bycatch in gillnet fisheries.” Fisheries Science. May 9, 2026.
Image: © Yaroslaf | Dreamstime.com
