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Underwater acoustic pingers were tested in Brazil to evaluate the behavioral responses of tucuxi (Sotalia fluviatilis). Five pingers were evenly placed on a floating 100 m line set along the dolphins' swimming parth in and out of sheltered waters. Dolphin sighting frequencies were recorded for functional and dummy pingers and control trials. Dolphin sightings were significantly lower in areas where the pinger line was set. Sighting frequency was significantly lower with active pingers than in dummy or control trials, but there wre no significant differences between the dummy and control trials. Preliminary results suggest that acoustic pingers attached to gillnets may be used to successfully prevent tucuxi bycatch.