Evidence of Dolphin Bycatch Reduction With Upcycled Plastic Bottles Acoustic Reflectors Attached to Bottom-Set Gillnets

Gillnet bycatch is the primary global threat to marine mammals. In this study, the effectiveness of upcycled plastic bottles used as acoustic reflectors to reduce dolphin bycatch and their effect on target catch was evaluated. Observed trials with (treatment) and without (control) bottles in bottom-set trammel nets and bottom-set gillnets were conducted between November/2020 and April/2025. Across 318 sets (170 control; 148 treatment), bycatch per unit effort (BPUE; based on net length × soak time) was 7.14 × 10⁻⁷ in control sets and 0.86 × 10⁻⁷ in treatment sets, representing an 88% reduction in BPUE when acoustic reflectors were used. Mean catch of target species did not differ significantly between control (=107 ± 92 kg) and treatment (=118 ± 141 kg) sets. Acoustic monitoring showed that average franciscana dolphin (Pontoporia blainvillei) click detections, measured as detection positive minutes (DPM), did not differ significantly between control (DPM = 0.0125) and treatment (DPM = 0.0128) sets. These results demonstrate that plastic bottles used as acoustic reflectors in bottom-set trammel nets and gillnets reduced the bycatch of dolphins and had no effect on the catch of target species. Given its low cost and lack of impact on target-species catch, this method can be readily tested in other regions and, if effective, widely adopted to improve the conservation of coastal dolphin species.