Tests d'efficacité du répulsif acoustique CETASAVER à bord des chalutiers commerciaux français Résultats obtenus au cours des années 2007 et 2008

An acoustic repellent was developed by Ixtrawl and Ifremer to mitigate incidental catches of common dolphins in trawl fisheries. The system developed-which bears the name of CETASAVER-was developed after behavioural tests performed on groups of common dolphins. These tests conducted at sea for the European project Necessity showed that the trajectories of animals could be changed by this pinger. The CETASAVER emits a beam directing conical with an opening between 75 and 15 degrees. This allows directional less disturbing environmental noise and must be directed towards the opening of the trawl and the frequency ranges from 30 to 150 kHz. The signals are modulated and pulsed. The average sound level is 178 dB which gives 139 dB at the entrance to the trawl (type Le Drezen 151m). The optimal area location of the deterrent on the trawl was determined. Numerous trials were conducted with a pelagic trawl in commercial conditions, most often in the presence of scientific observers. Successions of test and standard tows were performed in order to get a rigorous comparison. The observations were conducted in the bass fisheries during seasons 2007 and 2008 and involved a total of 121 hauls with pinger and 129 without pinger. Incidental capture were respectively found in 5 and 10 hauls with comparative numbers of dolphins of 6 and 20. The results show a reduction in common dolphin bycatch of around 70% during the two years. The bootstraps shows the need to double the number of observations to reach a significant difference through the confidence intervals in numbers of dolphins.