Environmental DNA (eDNA) applications for the conservation of imperiled crayfish (Decapoda: Astacidea) through monitoring of invasive species barriers and relocated populations

Native crayfish species often face competition and displacement by non-indigenous invasive crayfishes. Management responses implemented to preserve imperiled crayfishes may include the construction of physical barriers to prevent the spread of invasive crayfishes, and movement of native populations to "ark" sites that have not yet been invaded. These strategies require ongoing monitoring to determine their effectiveness. We propose that environmental DNA (eDNA), genetic material identified from environmental samples, can be useful for assessing advancing invasions and imperiled freshwater species associated with management interventions. We monitored a series of management interventions intending to isolate the endangered Shasta crayfish Pacifastacus fortis (Faxon, 1914) from the invasive signal crayfish Pacifastacus leniusculus (Dana, 1852) in California, USA. We successfully detected P. fortis eDNA from two sites where it was known to occur, one site where its presence was uncertain, and one site (near an "ark" site) where it was believed absent. We also detected P. leniusculus eDNA from five sites it was known to occupy, but failed to detect its eDNA at two sites where it was believed to occur. We conclude with recommendations for improved eDNA monitoring of crayfish conservation and management interventions in the future.