UC San Diego

Passive acoustic monitoring (PAM) is commonly used to study behavior and population dynamics of soniferous fish species in a cost-effective, minimally invasive manner. However, understanding the strengths and limitations of PAM for this purpose requires an assessment of variability in CAS of target species as a function of time, space, and proximity of spawning fishes. In this study we evaluate temporal and spatial trends in CAS by Nassau Groupers (Epinephelus striatus) using an array of six hydrophones deployed at a large Nassau Grouper FSA on Little Cayman, Cayman Islands. We collected continuous data for nine days during the winter spawning season, and subsequently employed an automatic classifier to extract the embedded Nassau Grouper CAS. Using these data, we qualitatively and quantitatively analyzed variability in temporal trends across the spatial array with a Bayesian mixed effects model. We found a clear degradation in accuracy of temporal calling patterns at the FSA as distance from the spawning site increased beyond 200 meters, and observed higher correlations among the most proximal hydrophone pairs than the most separated pairs. Our model predicted strong effects of fish proximity, spawning behavior, and crepuscular periods on detected calling rates of Nassau Grouper that corroborate with and add to the present literature. Our findings suggest a high degree of variability within relatively short distances from a sonic target, thus imploring a need for spatial resolution in acoustic analyses.