Researchers at Newcastle University have found that attaching discarded plastic bottles to fishing nets can reduce dolphin deaths by 88 percent, without reducing the amount of fish caught.
Two studies, published in the journals Fisheries Research and Marine Mammal Science, tested whether empty drink bottles could serve as acoustic reflectors on gillnets. Gillnets are made of nylon and are nearly invisible to dolphins and other marine mammals both visually and acoustically. Dolphins use echolocation to navigate, and the bottles give them something to detect before they swim into the nets.
According to Phys.org, the idea was developed by Professor Per Berggren at Newcastle University. Plastic bottles with air inside reflect sound, while glass bottles with metal bolts inside produce a clinking sound. Both types alert dolphins to the presence of the nets.
The research team monitored more than 1,600 fishing net deployments across three countries. The first study covered surface-set driftnet fisheries in Zanzibar and Peru, as well as bottom-set nets in Brazil. Results varied by location. In Zanzibar and Peru, plastic bottles actually increased targeted fish catches. However, neither glass nor plastic bottles reduced dolphin, porpoise, or turtle bycatch in the surface-set fisheries in those two countries. In Brazil, plastic bottles on bottom-set nets produced the dramatic 88 percent reduction in dolphin bycatch.
Berggren, who is listed as both lead and senior author of the studies and holds the title of emeritus professor of marine megafauna conservation in the School of Natural and Environmental Sciences at Newcastle University, described the significance of the finding in direct terms.
"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," Berggren said. "Attaching plastic bottles to fishing nets can reduce dolphin bycatch globally and is something that every fisher can afford."
Accidental capture in fishing gear is the leading threat to marine mammals worldwide. Existing bycatch reduction devices can be expensive and are often out of reach for small-scale fishers in developing countries. The bottle method requires no special equipment and costs almost nothing.
Berggren also noted the environmental dimension of reusing waste materials. "It's also rewarding to know that we are using some of the plastic waste that spoils our oceans," he said. "The bottles are securely attached to the nets, and we did not lose any plastic bottle during the trials."
The team is now pushing for wider adoption of the method. "We are excited to share this method, spread the word, and work with governments and agencies around the world to encourage the adoption of this low-cost mitigation method to reduce marine mammal mortalities in fisheries," Berggren said. "This is genuinely recycling that rescues dolphins."
The researchers acknowledged that results differed across fishing types and regions, and that further trials will be needed to understand where and how the method works best. The studies represent the first large-scale, multi-country field trials of bottle-based acoustic reflectors on commercial fishing gear.
