Estuaries are dynamic systems with highly variable environments, and it is often difficult to assess how fish behavior changes in response to fluctuating abiotic factors. Passive acoustic monitoring can be conducted with high spatiotemporal resolution, and provides data on species of ecological and economic importance that are missed by traditional sampling methods. We used recordings of an estuarine soundscape to assess the relationship between fish calling activity and temperature. To determine calling activity, acoustic data were collected from a restored oyster reef in Pamlico Sound, NC. We identified a three week period during peak spawning season in June 2017 with a rapid and large temperature fluctuation. Ecologically and economically important species calling during this time included Atlantic croaker and spawning oyster toadfish, speckled trout, and silver perch. We developed an automated detection algorithm that detected fish calls, and then manually classified call types matching the above species of interest. Call rates from the identified calls were calculated for each species over time and we assessed the relationship between call rate and abiotic variables, specifically temperature.
Results/Conclusions
Estuarine fish vocalize primarily for reproduction, and behavior and calling activity vary by species. Overall calling activity, measured as sound pressure level (i.e. loudness) of the soundscape, doubled as temperature dropped below 20 degrees Celsius, but decreased three-fold as temperature increased above 25 degrees Celsius. This overall change in calling activity was primarily driven by call rates of the Atlantic croaker; this species dominated our recordings, and call rates varied inversely with temperature. Calling activity of silver perch and oyster toadfish also decreased when temperature rose above 25 degrees Celsius. Speckled trout was the only species whose call rate was not affected by temperature changes within this range. With the present threat of climate change and its accompanying extreme weather events, it is imperative to develop the ability to predict fish spawning behaviors and habitat use under these expected variable conditions. This study provides detailed baseline data on changes in fish behavior in response to temperature fluctuations, and is part of a larger study investigating fish responses to oyster reef restoration. Identifying calling activity of reef-using species can also provide additional insight into reef habitat use and help inform reef management decisions.