Identifying spawning sites and other critical habitat in lotic systems using eDNA “snapshots”: A case study using the sea lamprey Petromyzon marinus L.

to be present upstream of several potential barriers to migration, sometimes in significant numbers. Our results also show that the addition of a lamprey-specific fish pass at an "impassable" weir, although assisting in ascent, did not have any significant impact on eDNA concentration upstream after the pass had been installed. eDNA concentration was also found to be significantly correlated with both the number of fish and the number of nests encountered. The application of snapshot sampling techniques for species monitoring therefore has substantial potential for the management of low-density species in fast-moving aquatic systems.