Environmental DNA reflects spatial distribution of a rare turtle in a lentic wetland assisted colonisation site

Conservation translocations require robust post-release monitoring to
evaluate their success, which can be challenging to implement and
maintain. Monitoring techniques that can account for the dispersal and
cryptic nature of translocated animals are necessary to provide critical
information on persistence and distribution. In this study, we developed a
highly sensitive environmental DNA (eDNA) assay specific to the Critically
Endangered western swamp turtle (Pseudemydura umbrina), a species
currently undergoing trials of assisted colonisation. Actively filtering
sufficient volumes of water in lentic systems is difficult due to high
concentrations of clogging particulates, therefore we assessed the
viability of passive sampling in a controlled environment by submerging
filter membranes and directly extracting DNA. Active sampling detected P.
umbrina with a 97.6% detection rate, whereas passive sampling resulted in
an 8.3% detection rate. We then used a fine-scale eDNA sampling design and
radio tracked translocated P. umbrina at the assisted colonisation wetland
to investigate eDNA dispersal and spatial monitoring resolution. We
detected P. umbrina at 42% (7 / 17) of eDNA sample sites, and the
probability of a positive eDNA detection was negatively associated with
the distance of P. umbrina from the sampling site, indicating limited eDNA
dispersal from the source. Systems with low natural mixing and limited
eDNA dispersal provide an opportunity for high resolution spatial and
temporal monitoring via targeted eDNA approaches. This is beneficial for
monitoring rare species in these systems, as such high-resolution results
can provide insights on species presence, distribution, and microhabitat
use.