RIVER HERRING ENVIRONMENTAL DNA: ESTIMATING RATES OF SHEDDING, DECAY, AND TRENDS IN THE ENVIRONMENT

Abstract

River herring, (Blueback Herring [Alosa aestivalis] and Alewife [A. pseudoharengus]), were once abundant in North Carolina waters and were an economically important fishery but their populations across their ranges are smaller due in part to anthropogenic causes. A method of quantifying the spawning population sizes is needed because North Carolina’s turbid and large river systems make traditional sampling difficult. By detecting trace DNA shed by river herring, the relative abundances and locations of spawning could be more easily determined. In order to obtain accurate eDNA shedding and decay rates and gain a better understanding of the relationship between river herring biomass and eDNA concentrations, three mesocosm experiments were conducted. Two of these were time series experiments that used different quantities of herring in tanks of various sizes to determine how much eDNA is shed from known biomasses of fish. This led to the determination of a preliminary eDNA shedding rate (1.63x10-3 (ng/L)/h) and decay rate (2.64x10-6 (ng/L)/h) for river herring The third aquaria experiment which used increasing numbers of fish at regular increments of time indicated that a significant, linear relationship between biomass of river herring and amounts of eDNA in ambient water suggesting that there is potential for developing a quantitative model using eDNA. This relationship has been found to be positive using two different sampling methods: bottle top filters and the ANDe backpack.. Weekly sampling also occurred at 8 sites in the Neuse River and Tar-Pamlico River, with sampling at two sites along the Neuse River confirmed by electrofishing data. At many sampling locations eDNA concentrations remained high at the end of the spawning season when fish abundances had decreased. This is likely due to larvae or juveniles in the system or persistence of eDNA due to the slower decay rate. These data also showed that similar trends could be seen at inland locations, even between different river systems, but were less consistent between river systems closer to the mouth of the river and that river herring eDNA may persist in some areas even after the fish have passed through. The results of this work are a first step in developing a model to quantify eDNA sampling data for river herring in NC to estimate spawning populations, which has not been done previously and can be used for future monitoring projects.