The second depredation mitigation device trials were carried out on February 25 and 26, 2020. Those new prototypes include some of the changes identified at the end of the previous trials. Among those modifications, monofilament gill net and ramie were used instead of the linen fabric, the mobile part and the triggering system were improved, a new mounting system was tested, and the opening system was changed.
The first stage of the trials took place in the Nemausa diving pool in Nîmes, France (https://www.vert-marine.com/nemausa-nimes-30/). During this survey, 3 divers equipped with underwater cameras recorded the device deployement and descent. The second stage of the trials took place onboard a small boat on the Etang de Thau. During this second day, an experimental longline equipped with 4 devices was set.
Both surveys aimed at assessing the device behaviour during the line setting, the device deployment (triggering and descent fluidity along the branchline), the protection skills of the net, the device behaviour during the line hauling, the impact of boat speed on the triggering system, and the device storage.
Handling of the devices
Several issues still remained unsolved at the end of those trials, and the device is not fully operational. We are currently working on a third version of the prototype which will soon be tested. Our work will mainly focus on the identification of materials which can be used to design effective protection, and the improvement of the triggering system.
We would like to thank Auriane SERVAL, MARBEC trainee, who was fully invested in this survey. Thanks to Emilie BOULANGER, Romain BACH, Jules HELIOU (divers), Marc SORIA, Luc MARKIW, Ilan PEREZ, Romain GROS and the NEMAUSA aquatic center (Guillaume BARBOTIN and Annabelle BONIN).