Traditional trapping methods outperform eDNA sampling for introduced semi-aquatic snakes

Area of Science:

• Ecology
• Conservation Biology
• Environmental Science

Background:

• Invasive species management faces resource limitations, making regional-scale traditional surveys challenging.
• Environmental DNA (eDNA) sampling is a promising tool for invasive species detection, but its efficacy compared to traditional methods needs further investigation.
• Occupancy modeling offers a robust framework for comparing detection probabilities of different survey techniques.

Purpose of the Study:

• To compare the detection probability of environmental DNA (eDNA) and traditional aquatic trapping for two introduced watersnake species in California.
• To assess the efficacy of a newly developed qPCR assay for detecting invasive watersnakes.
• To inform invasive species management strategies by evaluating the strengths and weaknesses of eDNA versus traditional survey methods.

Main Methods:

• Developed and utilized a qPCR assay to detect the eDNA of Banded (Nerodia fasciata) and Northern (Nerodia sipedon) watersnakes.
• Collected water samples from 91 sites across California near known introduced populations.
• Deployed aquatic funnel traps at a subset of these sites to capture watersnakes.

Main Results:

• eDNA detected N. fasciata at one site, while trapping detected it at three sites.
• eDNA detected N. sipedon at one site, which was also the only site where trapping was successful for this species.
• Traditional trapping exhibited a higher detection probability than eDNA surveys for both species, with higher detection rates for N. sipedon than N. fasciata.

Conclusions:

• Traditional survey methods can offer higher detection probabilities than eDNA sampling for certain invasive species.
• Both eDNA and traditional methods showed higher detection success for N. sipedon compared to N. fasciata.
• Managers should compare eDNA and traditional survey methods within an occupancy framework to select the most effective approach for detecting new invasive populations.