Environmental DNA (eDNA) as an Alternative Method to Estimate Juvenile Alewife (Alosa pseudoharengus) Recruitment in Freshwater Systems.

Mann, Sharon*, Karen A. Wilson, University of Southern Maine

Estimating juvenile alewife (Alosa pseudoharengus) recruitment in their native nursery habitats is important because of the implications to alewife restoration efforts and food web dynamics. Alewife are keystone species that influence food webs by both bottom-up (most juvenile alewife are eaten before they reach maturity) and top-down control of large-bodied zooplankton (Daphnia spp). In some cases, where alewives are land-locked or introduced outside their native range, the top-down control of Daphnia spp can cause trophic cascades resulting in blooms of edible phytoplankton (>50 µm). Counting adult alewives as they enter freshwater systems to spawn does not translate to a good estimate of juvenile alewife recruitment. Estimating juvenile alewife is a laborious process which entails purse-seining after dark (alewife school during the day) and can cause unintended juvenile alewife fatalities. Here, we estimated juvenile alewife abundance on seven lakes that differed in size, alewife history, and base nutrients, using traditional seining methods and eDNA from water collected from a closed purse-seine. For each lake we collected 5 water samples, and used targeted qPCR assays to estimate eDNA derived gene copies and compared to juvenile alewife numbers and biomass. Our research provides an easier and less invasive method to estimate juvenile alewife recruitment for lake managers and state agencies involved in anadromous species restoration.