Linking environmental DNA and acoustic telemetry to monitor Striped Bass (Morone saxatilis) in an estuarine ecosystem

Environmental DNA (eDNA) is a promising tool for monitoring aquatic species, offering a noninvasive alternative to traditional fish sampling methods requiring capture. We compared methods to detect striped bass (Morone saxatilis) by eDNA as well as acoustic telemetry to determine seasonal presence/absence within an estuarine ecosystem. Additionally, we assess the suitability of the two detection methods through controlled laboratory trials as well as modeling of the eDNA transport within the system. We demonstrate that eDNA can be detected from a closed water system for up to 10 h after the fish were removed. In monthly eDNA water samples collected in the Saco River in Maine over 3 years, and acoustic monitoring of 41 striped bass using a receiver array along the river and close to Ram Island, our data reveal a previously undocumented overwintering population of striped bass in the system. We demonstrate good but not perfect overlap of eDNA and acoustic telemetry data and elucidate the respective shortcomings as well as strengths of the two different detection methods. We conclude that in a highly dynamic estuarine system the combination of the two methods is advantageous to characterize species migrations, because neither technique alone provides sufficient detail.