Date of Award

8-2026

Document Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Karen Wilsson

Second Advisor

Rachel Lasley-Rasher

Third Advisor

Catherine Miller

Abstract

The Kennebec River, Maine is home to three species of anadromous fish of the genus Alosa: alewife (A. pseudoharengus) and blueback herring (A. aestivalis), jointly referred to and managed as river herring, as well as American shad (A. sapidissima). These ecologically, economically, and culturally important fish populations are depressed compared to historic levels and have been subject to extensive restoration efforts. While spawning adults have been well-studied, much less is known about the juveniles including whether they engage in resource partitioning to minimize competition and facilitate coexistence. In Chapter 1, I use stomach contents to compare diets as well as δ¹³C and δ¹⁵N stable isotope values to compare isotopic niche, which integrates diet and habitat. Fish were sampled by beach seine across four tidal and salinity regimes: a freshwater non-tidal river, freshwater tidal river, freshwater tidal bay, and tidal estuary. In both measures, river herring showed evidence of partitioning resources with shad, but not with each other. In Chapter 2, I compare two survey techniques: hydroacoustics and environmental DNA (eDNA) to the Maine Department of Marine Resources (MeDMR) beach seine survey. Hydroacoustics characterized the spatial and size distributions of the fish community more thoroughly than the beach seine, but results suffered from an inability to identify species. Using species specific qPCR, eDNA detected river herring and shad near seine sites where these species were not caught. eDNA metabarcoding detected 8 fish species not caught in the beach seine, the beach

6 seine caught 3 fish species not detected by metabarcoding, and the two methods had 23 species in common. Overall, this thesis demonstrates that the Kennebec River is an important nursery habitat for juvenile alosines in addition to being a migration corridor and that adding novel survey methods to the current beach seine will better assess the population.

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