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. • The PERISCOP pressurised recovery device (PRD) aims at recovering live deep-sea fauna, following active sampling by manned or remotely-operated submersibles. It has been deployed almost a hundred times (93) since its initial design in 2006, at depths ranging from 800 to 3600 m. Its operation has now become almost routine, with the successful recovery of various hydrothermal vent megafaunal organisms (shrimp, crabs, annelids, mussels, fish,..), in excellent physiological condition. Several improvements of the system are presented in terms of reliability, depth of deployment, simplicity of use, and a focus is made on 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". Their respective uses are reported and discussed here, and while the active system proves more efficient, the simplicity of the passive compensator greatly improves reliability and ease of use. Finally, in the light of the field experience acquired with the PERISCOP PRD, various technical aspects of pressurised recovery are discussed, and further improvements are proposed. [ABSTRACT FROM AUTHOR]