| Summary |
Blueback Herring (Alosa aestivalis) and Alewife (A. pseudoharengus) are two threatened species in the genus Alosa that use eastern North Carolina's coastal rivers and estuaries to spawn. In North Carolina watersheds, river herring (Alewife and Blueback Herring) were once highly sought after by commercial and recreational fisheries, but since the mid-to-late 20th-century populations have been on the decline, with no signs of recovery. In this study we evaluated the ability of environmental DNA (eDNA) to monitor the movement of spawning populations and juvenile populations of river herring in the Roanoke River. In this study, eDNA from the two species of river herring were quantified using qPCR. Water samples were taken weekly along the Lower Roanoke River and its tributaries from January through November in 2021 and 2022. Since eDNA can be successfully detected and amplified within the river basin, eDNA sampling was used as a technique for monitoring river herring movements between Edwards Ferry and Plymouth, North Carolina for more than 80 weeks over two years. Our results indicated that we successfully detected adult river herring spawning populations in the watershed from January until May, and juvenile herring from late May through the end of August. The same methods used for sampling site locations near each other showed similar detection success although the timing in changes in eDNA concentration differed. We confirmed that eDNA presence and concentration were positively correlated with the peak spawning temperatures described in the literature. It was found that eDNA concentration during adult spawning, and when juveniles are utilizing the watershed as nursery habitat, showed a significant asymptotic relationship with dissolved oxygen. Conductance had a significant positive linear relationship with eDNA concentration during spawning activity and a negative linear relationship post spawn. Though eDNA concentrations were greater in the spring when spawning adults were utilizing the watershed, a pattern of increased and subsequent decreased eDNA concentrations was detected in late summer and early fall each sampling year, which we attributed to juvenile river herring activity within the watershed. We conclude that river herring use of the Roanoke River watershed can be estimated using eDNA methods and environmental eDNA conditions for all life stages to obtain a complete view of the population. |
