Date of Award

Spring 5-6-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)


Wildlife Ecology and Wildlife Conservation


Joseph Zydlewski

Second Committee Member

Erik Blomberg

Third Committee Member

Stephen Coghlan, Jr.

Additional Committee Members

Hamish Greig

Joan Trial


Dams interrupt river connectivity and disrupt fish migrations. We used telemetry to study the migratory movement patterns of adult American shad, sea lamprey, and Atlantic salmon on the Penobscot River, Maine after dam removals and other passage improvements had occurred. We also studied scale formation of marine-stage Atlantic salmon raised in marine net pens, the findings from which could be relevant to captive rearing efforts.

American shad now have access to the majority of their historic spawning habitat, contingent on passage the first main-stem dam (Milford Dam). We found that habitat upstream of dams was infrequently accessed, and first time spawners were most likely to pass Milford, suggesting that passage motivation may be related to downstream spawning habitat saturation. Sea lampreys provide important ecological services within their native range. Passage success of tagged lampreys at Milford was relatively high, but passage success at upstream dams was variable. The insights provided by this study are an important first step towards ensuring that lampreys will persist in their native habitats.

Although fish passage exists at Milford Dam, it does not appear to be efficient for Atlantic salmon. Most salmon experienced extended delays at Milford Dam. Salmon also had low passage efficiencies when approaching dams elsewhere in the system. Most adults in the Penobscot are hatchery-origin fish stocked into the river as smolts, and current stocking practices release smolts downstream of Milford. This may prevent smolts from imprinting on upstream waters. We also found that fish that searched for passage at Milford near the fishway entrance experienced shorter delays compared to fish that searched throughout the river channel. Many study fish passed the dam on the same day as entering the fishway, suggesting that attraction to the fishway is a major factor leading to delays.

The rate at which scale circuli are formed can yield valuable information about fish growth. Scales were collected from Atlantic salmon raised in marine net pens to characterize circulus deposition and scale growth in relation to time and water temperature during the early marine phase. Deposition and growth rates were variable through time and when related to temperature.