A review and inventory of cabled and radio-linked hydrophones for passive acoustic monitoring of marine mammals.

Abstract

Fixed cabled hydrophone (FCH) and radio-linked hydrophone (RLH) systems are permanently, or semi-permanently, installed acoustic monitoring systems that are located on or moored to the seafloor. These systems have the capability to passively monitor bio-acoustic signals from marine mammals and, therefore, have great potential for monitoring and mitigation of potential impacts caused by anthropogenic activities. As part of a Joint Industries Programme sponsored effort, we reviewed past and present FCH and RLH systems with respect to their capabilities, advantages/disadvantages, and effectiveness for monitoring marine mammals in relation to oil and gas exploration/production activities. Based on this review, we provide examples and applications of these technologies. FCHs are typically powered by an external source and send data continuously to a receiving station that is usually located on shore. RLHs are moored or fixed to the seafloor, and transmit acoustic signals via radio-waves to a receiving station on shore. Both these systems allow acoustic data to be remotely monitored and processed in (or near) real-time. Hybrid systems can offer a good compromise between cost and capability by providing near real-time data transmission/processing with greater flexibility in deployment possibilities, but are usually limited in longevity and bandwidth of monitoring.