Gulf Toadfish (Opsanus beta) Boatwhistle Calls—A Prevalent Acoustic Cue with Passive Acoustic Monitoring Applications

The Gulf toadfish (Opsanus beta) is a soniferous and abundant species native to Gulf of Mexico estuarine environments—now considered a likely invasive species in coastal Brazil. Males produce distinctive boatwhistle calls during their reproduction behaviors, offering an acoustic cue for ecological functions such as mate selection, prey detection, and predator avoidance. Their calls can also be readily detected with passive acoustics to monitor Gulf toadfish distributions and serve as acoustic indicators for their preferred nesting habitats. In this study, we describe the spatial, annual, seasonal, monthly, daily, daytime, and diel variation of Gulf toadfish call occurrence in Cedar Key, Florida (USA), with multiple sampling efforts at seagrass and dock sampling locations in the years 2019–2022. From April through June during our dock sampling, calls were detected across almost all our sampled dates and often every hour of the day, with daily and diel fluctuations in call occurrence. In our seagrass meadow sampling, call occurrence showed some positive correlation with manatee grass (Syringodium filiforme) and salinity. Moreover, snapshot recordings as short as 5 min were sufficient to detect calls in 37 of our 45 sampling events compared to only five where trawls captured Gulf toadfish. Our findings demonstrate the efficacy of listening to Gulf toadfish calls for monitoring applications and can support future efforts seeking to understand the availability of a prevalent acoustic cue in estuarine soundscapes.