Using acoustically visible gillnets to reduce bycatch of a small cetacean: first pilot trials in a commercial fishery

•An acoustically visible gillnet was used in a commercial fishery first the first time.•Bycatch of harbor porpoises was reduced in numbers, but the sample size was low.•The gillnet modification had no effect on the catch efficiency of bottom-dwelling species.•A power analysis showed that 130 hauls are necessary for robust statistical assessment.