Performance of remote acoustic receivers within a coral reef habitat: implications for array design

Remote monitoring technologies are increasingly being implemented in the marine environment to better understand the movement patterns of taxa. Coral reefs are no exception. However, there is a paucity of information relating to the performance of acoustic receivers on coral reefs. Our results suggest that the detection performance of acoustic receivers may be significantly impacted by the unique nature of the reef environment. This study assessed the performance of passive acoustic receivers on a typical inner-shelf fringing reef, Orpheus Island, on the Great Barrier Reef, Australia. The detection range and diel performance variability of acoustic receivers was assessed using two parallel lines of 5 VR2W receivers spanning 125?m, deployed on the reef base and reef crest. Two 9-mm acoustic transmitters were moored at opposite ends of each receiver line. The working detection range for receivers was found to be approximately 90?m for the transmitter moored on the reef base and just 60?m for the transmitter moored on the reef crest. However, the detection range on the reef crest increased to 90?m when just the reef crest receivers were considered, highlighting importance of optimal receiver deployment. No diel patterns in receiver performance or detection capacities were detected, suggesting that no corrections are required when interpreting nocturnal versus diurnal activity patterns. We suggest that studies aiming for complete coverage of a site within a reef environment will require receivers in close (<100?m) proximity, and that the placement depth of receivers must be a major consideration, with shallow receivers exhibiting a greater detection range than those on the reef slope. Our results highlight the challenges imposed by coral reefs for acoustic telemetry and the importance of receiver placement for studies conducted within these habitats.