Update of the PERISCOP system for isobaric sampling of deep-sea fauna

We here present an update of the PERISCOP pressurised recovery device (PRD), which has allowed the recovery of live deep-sea fauna, following active sampling by manned or remotely-operated submersibles. It was designed in 2006, has since been deployed almost a hundred times (93), and its operation has now become almost routine. Various hydrothermal vent megafaunal organisms (shrimp, crabs, annelids, mussels, fish,..) were successfully targeted and recovered, allowing access to samples in excellent physiological condition. Gradually, the system was modified, aiming at improved reliability, depth of operation, and simplicity of use, especially regarding its compensator, i.e. the system that compensates for pressure loss experienced during ascent through the water column. Two types of compensators are presented, called “active” and “passive” (with so-called “water-filled” or “oil-filled” modes regarding the latter). Their respective uses are reported and discussed here, and while the active system proves more efficient (recovering at minimum pressure in the range 93.8–98.2% of in situ pressure, as opposed to 80.9–86.6% for the water-filled passive system, while no compensation leads to a range of 63.5–73.0%), the simplicity of the passive compensator greatly improves reliability and ease of use and maintenance. Finally, the monitoring of pressure and temperature of the PRD and the surrounding water column permits to discuss various technical aspects of pressurised recovery, and to propose further improvements.