Adult Atlantic Salmon Movements And Mortality In The State Of Maine

Atlantic salmon, Salmo salar, populations in the United States have been extirpated from much of their historic habitat and remain at critically low levels despite their ecological, economic, and cultural importance, with the last remaining runs located in the State of Maine. We used acoustic telemetry to track the movements, survival, and habitat use of adult Atlantic salmon from 2022 to 2024 between two rivers in Maine: The Penobscot and Machias. In Chapter 1, we investigated the movements and survival of post-spawn Atlantic salmon (N = 112) in the Penobscot River, Maine. Despite being an endangered species in the State, the downstream movements of post-spawn adults, also known as kelts, remain poorly understood. We set out to better understand the downstream movements and survival of kelts after release. Our findings indicated that 54% of kelts exhibited rapid movement seaward after release instead of overwintering, contradictory to previous studies. Notably, kelts that moved out immediately post-release experienced greater mortality compared to those that overwintered. We estimated apparent mortality to be around 83%, with higher mortality probabilities occurring near the dams and release areas. Furthermore, we observed that 55% of fish passed a dam when the designated downstream passages were closed. In Chapter 2, we monitored the movements of Atlantic salmon (N = 270) released into a dammed (Penobscot) and undammed (Machias) river and were reared in a recirculating aquaculture system (RAS) as part of a pilot smolt-to-adult supplementation (SAS) program. Our results reveal differences in movement behavior: salmon in the Penobscot River tended to overwinter, whereas those in the Machias River moved directly downstream after release. Overall, salmon released during the summer displayed more exploratory movements compared to those released in the fall. Among all release years, mortality was 67%. The majority of salmon either left the river shortly after release (5- 30 days) or the following spring (>120 days), with release year being the most influential variable in whether a fish exited the river or not. While site fidelity averaged 47% during the study, it was notably higher for fall- released salmon (76%) compared to summer released (23%). These findings suggest that releasing sexually mature adults in the fall may enhance site fidelity and improve the likelihood of successful spawning in the wild. Overall, these chapters highlight the complex dynamics of Atlantic salmon movements and survival in Maine, emphasizing the significant impact of dams on post-spawn kelts and the potential benefits of strategic release timing in restoration efforts.