To reduce incidental catch of cetaceans in gillnets, two forms of acoustic modifications are reviewed here; one to make gillnets more reflective to cetacean sonar, and another using active sound emitters in nets to alert cetaceans to the presence of nets. A review of the literature shows that neither strategy has proven indisputably effective. Air-tube nets and multifilament nets used in the North Pacific Japanese driftnet fishery for salmon have caught fewer Dall’s porpoises than equivalent standard gillnets. However, results were not consistently significant over several years, and have not been confirmed by a thorough study of modified gillnets in another driftnet fishery. Studies examining effects of adding sound emitters to gillnets have also proven inconclusive. Further, there appear to be serious problems with the logical basis for acoustic net modification strategies. I argue that such strategies are not likely to achieve the reductions in cetacean bycatch that are required to conserve several dolphin and porpoise species and propose alternative methods which are likely to be more effective.