Date of Award

Fall 12-20-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Joseph Zydlewski

Second Committee Member

Erik Blomberg

Third Committee Member

Danielle Frechette

Abstract

Sea Lamprey are a native species in Maine’s rivers and provide many ecosystem services, including substrate aeration, food web linkages, and nutrient subsidies. Sea Lamprey populations have been in steep decline due to widespread habitat fragmentation resulting from the construction of dams, culverts, and road-stream crossings. A series of river connectivity improvements in the Penobscot River basin recently increased habitat access for diadromous fishes, but the effects of these changes are still being assessed. We used eDNA and radio telemetry to assess the current extent of habitat use and dam passage for Sea Lamprey in the Penobscot River. We then compared these results with previous studies and historical data to quantify changes in Sea Lamprey distribution through time. Our results show that the distribution of Sea Lamprey decreased by 84% between the 1800’s and 2007. Restoration efforts have increased the species’ distribution by 45% between 2007 and 2023. However, the species remains limited to only 23% of their historical range. Extant dams continue to prevent the expansion of Sea Lamprey by impeding passage. Many Penobscot River dams lack fish bypasses and passage performance is highly variable among dams with fishways (0%-96% overall passage success between 2020 and 2023). Improved passage at dams remains an important direction for restoration of these native fish.

Alewives are a native, diadromous species in Maine’s Kennebec River but have greatly decreased in abundance as a result of widespread damming. The species was extirpated from Togus Stream, a tributary of the Kennebec River, in 1804 upon the construction of the Lower Togus Pond Dam, which initially had no fishway. However, Alewives were recently reintroduced via stocking and a pool-and-weir fishway has been installed to restore connectivity between Togus Stream and Lower Togus Pond. To evaluate the effectiveness of the fishway, we PIT tagged 706 Alewives and tracked their movements through the fishway. We modeled passage success with time-to-event and found that success was positively related to fork length and temperature, and negatively related to water depth, number of attempts, and capture location (fish which had been captured within the fishway experienced lower passage success). Overall, 78% of tagged fish successfully passed the fishway. The median transit time of the fishway was 38 minutes. Individuals spent on average 18 minutes at the 90-degree turn pool and 9 minutes at the 180-degree turn pool. The overall performance of the Lower Togus Pond fishway was comparable with other recently installed fishways but was much higher than many older fishways, indicating that advancements in fishway engineering are positively affecting Alewives in Togus Stream and beyond.

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