Date of Award

Spring 5-6-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Wildlife Ecology and Wildlife Conservation


Joseph Zydlewski

Second Committee Member

Stephen M. Coghlan Jr.

Third Committee Member

Daniel Hayes


The Penobscot River Restoration Project was a large river rehabilitation project, culminating in the removal of the two lowermost dams (Veazie and Great Works) and improvements to fish passage on several remaining dams. Fish assemblages were surveyed for 3 years prior to rehabilitation, 3 years after, and now 8 years post-rehabilitation. Approximately 475 km of shoreline was sampled via boat electrofishing, yielding 133,394 individual fish of 41 species. The greatest shifts in assemblage structure occurred immediately after dam removal in formerly impounded sections, with increased prevalence of riverine and migratory species. Extended sampling documented several additional changes occurring within lower tributaries and tidally influenced river segments. Large schools of adult and young of the year alosines have increased in abundance upstream of the lowermost dam site although this area remains dominated by lacustrine species. Adult anadromous fishes continue to be in greatest abundance immediately below the Milford Dam. Our results provide continued evidence that dam removal results in fish assemblages dominated by riverine and anadromous species in previously impounded habitats, while upgraded fish passage has partially reconnected migratory species with historic habitat. While two new species were detected during the extended sampling effort, we observed an overall increase in the frequency of occurrence and spatial distribution of White Catfish (Ameiurus catus) within the lower portion of the Penobscot River. White Catfish have declined in their native range due to competition with introduced ictalurid catfish. Outside their native range, however, these fish have expanded their range northward along the Atlantic coast. White Catfish did not exist in Maine until recently. An introduction has allowed this species to establish in several coastal rivers in the state including the lower Penobscot River downstream of Milford Dam. Upstream access was gained following the two dam removals. Incorporation of a fish elevator at the third, Milford Dam, provides additional upstream access. Long-term boat electrofishing surveys revealed increases in the encounter rate for White Catfish (26%) coinciding with declines (45%) in the native Brown Bullhead, Ameiurus nebulosus. White Catfish are now poised to expand into habitat upstream of the dam. Electrofishing and baited trotline surveys demonstrated that the species is abundant within the tidally influenced freshwater, with one individual detected upstream of the Milford Dam. We compared age and growth via otoliths using fish captured at the Milford Dam and from the tidal reaches of river. Estimated growth parameters were consistent with populations from other Atlantic coastal rivers. Otolith cross sections were then analyzed for strontium and barium (Sr and Ba) using LA-ICP-MS to infer movements between fresh water and elevated salinities. We observed no notable changes of Sr or Ba, suggesting no discernable movements into elevated salinities. Together, these data suggest these fish have been established in the lower river, out competing brown bullhead where they co-occur and will likely continue impact the ecology of the upper Penobscot River as they continue to become establish.