Localizing individual soniferous fish using passive acoustic monitoring

Identifying where fish inhabit is a fundamentally important topic in ecology and management allowing acoustically sensitive times and areas to be prioritized. Passive acoustic localization has the benefit of being a non-invasive and non-destructive observational tool, and provides unbiased data on the position and movement of aquatic animals. This study used the time difference of arrivals (TDOA) of sound recordings on a four-hydrophone array to pinpoint the location of male oyster toadfish, Opsanus tau, a cryptic fish that produces boatwhistles to attract females. Coupling the TDOA method with cross correlation of the different boatwhistles, individual toadfish were mapped during dawn (0523-0823), midday (1123-1423), dusk (1723-2023) and night (2323−0223) to examine the relationship between temporal and spatial trends. Seven individual males were identified within 0.5-24.2 m of the hydrophone array and 0.0-18.2 m of the other individuals. Uncertainty in passive acoustics localization was investigated using computer simulations as <2.0 m within a bearing of 033 to 148° of the linear hydrophone array. Passive acoustic monitoring is presented as a viable tool for monitoring the positions of soniferous species, like the oyster toadfish. The method used in this study could be applied to a variety of soniferous fishes, without disturbing them or their environment. Understanding the location of fishes can be linked to temporal and environmental parameters to investigate ecological trends, as well as to vessel activity to discuss how individuals' respond to anthropogenic noise.