Topography and biological noise determine acoustic detectability on coral reefs

Abstract

Acoustic telemetry is an increasingly common tool for studying the movement patterns, behaviour, 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 topography with biological and environmental noise have not been quantified on coral reefs. We conduct two long-term range tests (one and four months 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 detection 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 four month test, suggesting a strong influence of biological noise (reducing detection probability up to 30%), notably more influential than other environmental noises, including wind-driven noise, which is normally considered important in open-water environments. Analysis of detections should be corrected in consideration of the diel patterns we find, and range tests or sentinel tags should be used for more than one month to quantify potential changes due to lunar phase. Some studies assume that the most usual factor limiting detection range is weather-related noise; this cannot be extrapolated to coral reefs.

Environmental factors influence the detection probability in acoustic telemetry in a marine environment: results from a new setup

“…This detection range is in the range of previous reports, which encompass both higher (Hobday & Pincock, 2011;Huveneers et al, 2016) and similar range values (Welsh et al, 2012;Cagua et al, 2013, Stocks et al, 2014. Some other publications have reported a broad range of distances within the same study (How & de Lestang, 2012;Cagua et al, 2013;Gjelland & Hedger, 2013). Although the detection ranges differ extensively between the cited studies, they all concluded that detection range strongly depends upon meteorological and oceanographic environmental variables, on sediment characteristics and on the environment's topographic complexity factors which all influence sound propagation in water.…”

“…The present study demonstrates that there is a good detection probability up to 200 m, but it quickly reduces beyond this distance. This detection range is in the range of previous reports, which encompass both higher (Hobday & Pincock, 2011;Huveneers et al, 2016) and similar range values (Welsh et al, 2012;Cagua et al, 2013, Stocks et al, 2014. Some other publications have reported a broad range of distances within the same study (How & de Lestang, 2012;Cagua et al, 2013;Gjelland & Hedger, 2013).…”

Close proximity detection interference with acoustic telemetry: the importance of considering tag power output in low ambient noise environments

“…The absence of CPDI from the Jupiter study site detection range profile is consistent with the results of Cagua et al [13]. They found, in a high ambient noise coral reef environment, the highest detection proportion occurred at 0 m distance, with progressively decreasing proportions thereafter, for both V16-H and V13-H tags.…”

Can you hear me now? Range‐testing a submerged passive acoustic receiver array in a Caribbean coral reef habitat

“…Cagua et al. () performed robust range‐testing at two sites on a platform reef in the Red Sea using fixed delay interval V13‐1x (153 dB) and V16P‐6H (160 dB) tags (Cagua et al. ).…”