Automated acoustic detection of river herring (Alewife and Blueback Herring) spawning activity

Abstract

Objective: We used passive acoustic monitoring (PAM) and automatic detection of spawning splashes to examine the timing and environmental drivers of spawning in river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis). Methods: Acoustic recordings of spawning splashes were collected from March to May 2021 in the Choptank River, Maryland, using an AudioMoth recorder. Recordings were analyzed using a random forest model on the Rainforest Connection ARBIMON platform to determine hourly presence–absence of splashes. Result: At a seasonal scale, our results suggested two peaks in spawning activity: early March and mid-April, corresponding with the known phenologies of Alewife and Blueback Herring. Hourly patterns in spawning activity suggested distinct diel cycles, with spawning most concentrated at dawn. In contrast, sonar fish counts collected for 1 week during the season indicated that migration occurred throughout daylight hours. We also found a potential relationship between spawning activity and the presence of great blue herons Ardea herodias. Conclusion: Overall, our results demonstrate that PAM can be an efficient and affordable method for studying the spawning ecology of anadromous fish.