Environmental DNA (eDNA) Successfully Detects Invasive Rusty Crayfish Orconectes rusticus at Low Abundances

Early detection is vital for the management and control of species invasions, and environmental DNA (eDNA) is emerging as an important monitoring tool to this end. We tested the ability of eDNA to detect invasive rusty crayfish (O. rusticus) presence and represent abundance of this species in 12 lakes of Vilas County, Wisconsin during the summer of 2014. These lakes were chosen to represent a known gradient of O. rusticus absence to high abundance. We estimated O. rusticus abundance by baited trapping at lakes, and paired these trap locations to 10 surface water samples per lake that were filtered for eDNA and sequenced as quantitative PCR (qPCR) on primers developed for O. rusticus. We successfully detected O. rusticus presence by eDNA down to catch-per-unit effort (CPUE) as low as 0.17 crayfish per trap, and the proportion of water samples yielding positive detections of O. rusticus increased with increasing CPUE – although the relationship with abundance was fairly weak (R2 = 0.48). Our study demonstrates that eDNA may have high utility in monitoring for early detection of invasions by crayfish like O. rusticus, and we anticipate that further methodological advancements may yet improve on these results.