Fishery interactions pose the most significant direct anthropogenic threat to marine mammals. In this study, we tested the effectiveness of acoustic alarms at reducing the bycatch of cetaceans by small-scale gillnet vessels operating from the northern Peru port of Mancora. We equipped nets with 10 kHz pingers for vessels targeting sharks, tuna, dolphin-fish, and rays. We monitored a total of 313 sets in 60 trips. We found that small cetacean bycatch per unit effort (BPUE) was reduced by 83% in experimental nets compared to control nets, with no observed reduction in whale BPUE. The study also found that pingers did not negatively affect catch rates of target species such as rays and bony fishes. However, sets with pingers had a reduction in shark catch per unit effort (CPUE) of 32.9%. Given the high number of humpback whale (Megaptera novaeangliae) entanglements we observed, we recommend testing of lower frequency “whale” ping-ers. We also encourage larger scale implementation of pingers for small cetaceans given the potential shown here to reduce gillnet bycatch mortality by thousands of animals annually.