Abstract

The use of passive acoustics to monitor sound production at fish spawning aggregation (FSA) sites has facilitated an ability to crudely infer patterns of spawning and abundance in the absence of visual surveys. However, challenges in calibrating counts of detected fish sounds for time-varying, environmental effects on detectability (e.g. background noise) has limited the evaluation of relationships between sound production and levels of courtship behaviors, spawning, and abundance. Here, we used propagation modeling and detection theory to estimate rates of sound production from uncalibrated levels of detected sounds produced by territorial, male Gulf grouper (Mycteroperca jordani) during visual displays directed towards females as part of spawning bouts. Estimated of rates of sound production were compared to diver observations of courtship, spawning, and numbers of females within male territories. Environmentally calibrated, estimated rates of sound production differed from raw levels of detected sounds, highlighting the importance of incorporating detection theory into acoustic monitoring efforts at FSAs prior to making inferences about patterns in courtship, spawning, and abundance. Rates of sound production were greatest prior to sunset and were correlated to observed rates of spawning and females encountered within male territories, indicating that female presence and increased opportunities to spawn largely drive sound production in some territorial male groupers during reproductive periods. This study found that once calibrated for environmental effects and detection capabilities, changes in rates of fish sound production can be used to estimate levels of spawning activity and the abundance of both sexes at FSAs, thereby supporting the continued use of passive acoustics to monitor FSAs of soniferous species.

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