Movement and Survival of Atlantic Salmon Smolts in the Penobscot River, Maine

The Penobscot River system hosts the largest population of endangered Atlantic salmon Salmo salar in the United States. However, total adult returns in this river remain low. Historically low numbers led to listing of the distinct population segment (DPS) in 2000, and the Penobscot River population was included in the DPS in 2009. Reducing mortality in all life stages is crucial for the recovery of Atlantic salmon populations. One of the life stages associated to high mortality is the juvenile stage (smolts), in which individuals migrate downstream towards the estuary. During this migration smolts face a series of new conditions such as novel predators, the physiological challenge of increased salinity, and dams. Dams are a primary cause for low abundance of this species in the Penobscot River, and dams remain a considerable source of mortality for smolts. Acoustic and radio telemetry was used to explore the survival, and movement of downstream migrating smolts. First, the historical survival and movement of smolts in the Piscataquis River, a major tributary of the Penobscot River, was investigated, with particular emphasis on the effects of dams on delays. System-wide survival from 2015-2019 was obtained and compared to survival in previous years in the Penobscot River. A decision making tool for evaluating survival of smolts was developed, and an experiment for analyzing the phenology and energetic effects on individual physiological responses