Diurnal shifts in eDNA concentration of threatened juvenile river herring

River herring, <i>Alosa</i> species, are threatened in North Carolina waters. Environmental DNA (eDNA) is a non-invasive approach to monitor their movement. River herring, particularly juveniles, are known to exhibit diurnal shifts within water columns. To assess how this influenced the detection of eDNA concentrations from fish, water samples were collected from the Roanoke River during the day and night of the same day for four weeks. Using qPCR analyses, we found that nighttime eDNA concentrations consistently exceeded those of daytime concentrations indicating night is a better time to sample. If night sampling is infeasible, consistency in sampling time is important.