F. Cagua, M. Berumen, E. Tyler
Coral Reefs, 32, pp. 1123-1134, (2013)
Passive monitoring , Acoustic transmitters, Detection efficiency, Saudi Arabia
Acoustic telemetry is an increasingly commontool for studying the movement patterns, behavior and site fidelity of marine organisms, but to accurately interpret acoustic data, the variability, periodicity and range of detectability between acoustic tags and receivers must be understood. The relative and interactive effects of topog-raphy with biological and environmental noise have not been quantified on coral reefs. We conduct two long-term range tests (1- and 4-month duration) on two different reef types in the central Red Sea to determine the relative effect of distance, depth, topography, time of day, wind, lunar phase, sea surface temperature and thermocline on detec-tion probability. Detectability, as expected, declines with increasing distance between tags and receivers, and we find average detection ranges of 530 and 120 m, using V16 and V13 tags, respectively, but the topography of the reef can significantly modify this relationship, reducing the range by* 70 %, even when tags and receivers are in line-of- sight. Analyses that assume a relationship between distance and detections must therefore be used with care. Nighttime detection range was consistently reduced in both locations, and detections varied by lunar phase in the 4-month test, suggesting a strong influence of biological noise (reducing detection probability up to 30 %), notably more influential than other environmental noises, including wind-drivennoise, which is normally considered important in open-water environments. Analysis of detections should becorrected in consideration of the diel patterns we find, and range tests or sentinel tags should be used for more than1 month to quantify potential changes due to lunar phase. Some studies assume that the most usual factor limitingdetection range is weather-related noise; this cannot be extrapolated to coral reefs.