A pinger experiment was carried out on the French trammel net fishery in the marine protected area off the west coasts of Britanny in order to compare acoustic mitigation measures for harbour porpoise. Three types of pinger devices (Aquamark 100, Pinger V02, DDD02) were used for porpoise mitigation in the area where no bycatch estimation has previously been made. The pingers DDD02 were attached at each end of the net near the anchor. The pinger Aquamark and pinger V02 were attached to the headline of the nets and were spaced by 400 m and 200 m respectively. The EC regulation 812/2004 requires a such pilot study. Observers at sea were deployed on board of 10 fishing vessels from Le Conquet and Audierne harbours. During one year, 462 km of control nets (non equipped nets) and 150 km of equipped nets shared between the three systems were observed in order to compare bycatch, as well as physical reliability and practicability of pingers. Three harbour porpoises Phocoena phocoena were caught on the control nets whereas two porpoises and two grey seals Halichoerus grypus were recorded in the nets equipped with Aquamark 100. The bycatch rate was 0.006 porpoise per km on the control nets and twice more on the pingered nets and more precisely six times more for those equipped with the Aquamark. No statistical test can be performed due to the small numbers of bycatches observed. The practicability, reliability and costs were also analysed for each pinger type. All the results are discussed in relation to mitigation measures and regulations.