A review of fixed autonomous underwater recorders

Autonomous underwater recorders (ARs) are fixed passive acoustic electronic systems that acquire and store acoustic data internally (i.e., without a cable or radio link to a receiving station). They are deployed semi-permanently underwater (via a mooring, buoy, or resting on the sea-floor) and must be retrieved after the deployment period to access the data. ARs are capable of monitoring and recording underwater sounds over a wide range of spatial and temporal scales. As part of a Joint Oil & Gas Industry Program on Sound and Marine Life (JIP) sponsored effort, we reviewed over 30 ARs that are available for recording marine mammal sounds. They varied greatly in price and capabilities, from small hand-deployable units for detecting dolphin and porpoise clicks in shallow water to large units that can be deployed in deep water and record wide frequency bands for long durations. Considerations to weigh when selecting which device to use include price, longevity and depth of deployment, area to be monitored, and, most importantly, the bandwidth and the characteristics of sounds to be monitored (i.e., marine mammal call types and noise sources).