Date of Award

Summer 8-22-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Wildlife Ecology and Wildlife Conservation

First Committee Advisor

Joseph Zydlewski

Second Committee Member

Danielle Frechette

Third Committee Member

Christina Murphy

Abstract

The first chapter of this thesis examines the complex history and ecology of anadromous fish restoration in the St. Croix River, an international waterway between Maine, USA and New Brunswick, Canada. Once supporting one of North America's largest river herring migrations - with historical estimates ranging from 12-58 million fish annually - the St. Croix watershed exemplifies the challenges and potential of recovering migratory fish populations following centuries of anthropogenic impacts. This research details alewife (Alosa pseudoharengus) life history and ecological significance, highlighting their role in cross-ecosystem nutrient transport between freshwater and marine systems. Through analysis of the watershed's governance frameworks, including the International Joint Commission and St. Croix International Waterway Commission, this study documents how transboundary cooperation has evolved to address fisheries management. Particular attention is given to the contentious alewife management of the 1990s-2010s, where competing stakeholder interests - recreational fishing guides, industrial users, conservation advocates, and Passamaquoddy Tribal members - influenced policy decisions regarding fish passage at critical dams. The chapter illustrates how Indigenous leadership, scientific research, and adaptive governance ultimately resolved this conflict, leading to reopened fishways and initial population recovery. With alewife numbers increasing from a mere 900 fish in 2002 to over 840,000 in 2023 following legislative changes, the St. Croix case study demonstrates both the persistent challenges of restoration and the potential for recovery when ecological, cultural, and economic values are considered in watershed management. The second chapter investigates how the restoration of anadromous fish populations in the St. Croix River depends critically on passage success at mainstem barriers. Following the 2024 removal of Milltown Dam, two major upstream barriers remain: Woodland Pulp and Grand Falls Dams, which block access to 94% of historical spawning habitat. We investigated adult alewife approach and passage behavior at both facilities using radio telemetry during the 2022 and 2023 spawning migrations. Fish were collected by electrofishing, gastrically tagged (n=229 in 2022; n=350 in 2023), and tracked using radio telemetry near the dams. At Woodland Pulp, only 43% in 2022 and 23% in 2023 of tagged fish approached the dam. Of those that approached in 2023, 50% showed preference for the northern channel where no passage was available. Of fish that approached, only approximately 14% successfully passed. At Grand Falls, approach and passage rates varied between release groups. Fish in the group that were transported and released upstream of Woodland Pulp showed higher passage success (42%) at Grand Falls compared to those in the group released directly below Grand Falls (4.5%). These findings suggest that both attraction to and passage through the existing fishways present significant challenges to restoration. Results from this study will inform upcoming passage improvement projects at both facilities. In the third chapter, we address downstream movement, as it remains comparatively understudied to that of upstream fish passage for river restoration efforts. Successful downstream movement may prove equally important to population recovery, particularly for iteroparous species like alewife (Alosa pseudoharengus). Using radio telemetry, we investigated the downstream migration approach and passage of adult alewife at same two hydroelectric facilities, examined in Chapter 2. At Woodland Pulp Dam, we found that nearly 61% of tagged fish that were released above the facility subsequently approached the dam heading downstream, with 90% ultimately selecting the northern headdam spillway route rather than the designated fishway (3.3% used fishway, 6.7% used an undetermined route). These fish demonstrated short search times (median 3.6 hours) and 100% passage efficiency. At Grand Falls Dam, the second dam on the river, 90% of tagged fish that were released above this dam approached the facility, with 52% utilizing the sluiceway route, 37% using the fishway, and 9% failing to pass. Fish at Grand Falls exhibited significantly longer search times than fish at Woodland Pulp – (median 43.9 hours for fish that took the fishway, and median 49.6 hours for fish that took the sluiceway). Despite high individual dam passage rates, only two fish from each release group were ultimately detected near the head of tide, suggesting significant post-passage mortality. These findings highlight the importance of considering not only passage efficiency but also passage quality, search time, and cumulative effects of multiple barriers when evaluating fish restoration progress. The differences in behavior between facilities also underscores the importance of site-specific passage solutions to ultimately support alewife population recovery in the St. Croix watershed. Collectively, this thesis provides evidence that successful alewife restoration in the St. Croix watershed requires integrated consideration of historical context, stakeholder engagement, and site-specific upstream and downstream passage solutions.

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