Discarded Plastic Bottles Save Dolphins From Nets

Discarded Plastic Bottles Save Dolphins From Nets

Researchers at Newcastle University have found that attaching discarded plastic bottles to fishing nets can help dolphins detect and avoid deadly gear, potentially reducing bycatch on a global scale.

The findings, published in the journals Marine Mammal Science and Fisheries Research, address the threat of gillnets. These nets, constructed from nylon, are nearly invisible both visually and acoustically to marine mammals. Because dolphins and porpoises rely on echolocation—sending out high-frequency clicks that bounce off objects to create acoustic images—they often cannot detect the thin mesh of a gillnet. According to the WWF, entanglement in fishing nets is the single largest cause of mortality for small cetaceans, with an estimated 300,000 small whales, dolphins, and porpoises dying each year.

The solution, developed by Professor Per Berggren, Emeritus Professor of Marine Megafauna Conservation at Newcastle University, utilizes upcycled waste. The team tested whether empty plastic bottles filled with air or glass bottles containing metal bolts could serve as low-cost reflectors.

Air-filled plastic bottles act as sound reflectors; when a dolphin's sound waves hit the bottle, the signal bounces back clearly, flagging the net as a barrier. Glass bottles with bolts function as "pingers" by producing a clinking sound. Both methods aim to make the nets acoustically visible without reducing the catch of target fish species.

The research was conducted across multiple global sites. An initial study monitored more than 1,600 net deployments in Brazil, Peru, and Zanzibar. In Peru and Zanzibar, the researchers found that plastic bottles increased targeted fish catches but did not reduce the bycatch of turtles, porpoises, or dolphins. However, the trials in Brazil showed promise for bottom-set gillnet fisheries.

To build on the Brazilian results, a second study was conducted between 2020 and 2025. This trial monitored 318 fishing trips, comparing standard nets to those fitted with plastic bottles. The results showed that the plastic bottle reflectors reduced dolphin bycatch by 88%, while the catch of commercially important fish remained unchanged.

"This is a good news story and something that we strive for - a simple solution which benefits both dolphins and the fishers who use the gear. Attaching plastic bottles to fishing nets can reduce dolphin bycatch globally and is something that every fisher can afford."

Per Berggren, Emeritus Professor of Marine Megafauna Conservation, via miragenews.com

Professor Berggren suggested that the difference in success between bottom-set nets and surface-set nets might be due to surface water being a "noisier environment," which could reduce the efficacy of the reflectors.

The impact of these reflectors is particularly critical for vulnerable species. In Brazil, the trials targeted bottlenose and threatened Franciscana dolphins. The latter is listed as vulnerable and faces intense pressure across South America. In other regions, the crisis is even more acute; the vaquita porpoise in the upper Gulf of California has been reduced to fewer than 10 individuals due to gillnet entanglement, and an estimated 20,000 cetaceans are killed by bycatch in Peru annually.

Other low-cost technologies are also being tested. In Muncar, East Java, researchers with WWF-Indonesia are trialing solar-powered LED lights. While battery-powered lights have been used since 2011, solar versions remove the cost and pollution associated with frequent battery replacement. A 2020 paper indicated that illuminated nets reduced dolphin bycatch in a small-scale Peruvian fishery by almost 71 percent, while a 2022 study showed a 63 percent overall reduction in sea turtle bycatch.

Despite these advancements, challenges remain. The WWF notes that solutions successful in trials rarely make it to the entire fishing fleet. Additionally, the shift from natural fibers to strong plastic polymers in modern gear has made it nearly impossible for dolphins to break free once entangled.

Professor Berggren stated that the bottles used in the trials were securely attached and none were lost, providing a way to reuse plastic waste that otherwise spoils the oceans. The research team is now expanding its work, with further testing of plastic bottle reflectors currently underway in fisheries in Congo and Cambodia.