A surface trawl survey (2001-2005) in Penobscot Bay, Maine, U.S.A., and the nearshore Gulf of Maine waters was conducted to investigate early marine dynamics of a hatchery-dependent Atlantic salmon Salmo salar population from a severely modified river system. Data generated were used to evaluate the effect of stocking location and time on migration success and to describe the migratory pathways and environments that post-smolts traverse. Significant differences in early migration success were detected among different stocking groups, but subsequent marine survival was independent of stocking group. While the post-smolt population was primarily composed of hatchery origin smolt-stocked fish, other life-stage stocking strategies (i.e. parr stocking) represented a higher proportion of the population than previously assumed. Catch distribution suggests evidence of an initial marine migratory pathway out of the dynamic Penobscot Bay environment. The hypothesized benefits of a predator refuge based on the co-occurring species complex is considered minimal for emigrating post-smolts given a mismatch in the size overlap among species and low abundance of other co-occurring diadromous populations. These data can be used to modify current management actions to optimize S. salar recovery and inform future research agendas.

Determining the mechanisms driving range-wide reductions in Atlantic salmon marine survival is hindered by an insufficient understanding of their oceanic ecology and distribution. We attached 204 pop-up satellite archival tags to post-spawned salmon when they migrated to the ocean from seven European areas and maiden North American salmon captured at sea at West Greenland. Individuals migrated further north and east than previously reported and displayed increased diving activity near oceanographic fronts, emphasizing the importance of these regions as feeding areas. The oceanic distribution differed among individuals and populations, but overlapped more between geographically proximate than distant populations. Dissimilarities in distribution likely contribute to variation in growth and survival within and among populations due to spatio-temporal differences in environmental conditions. Climate-induced changes in oceanographic conditions will alter the location of frontal areas and may have stock-specific effects on Atlantic salmon population dynamics, likely having the largest impacts on southern populations.

To gain information on postsmolt dynamics of emigrating Atlantic salmon Salmo salar through Penobscot Estuary and Penobscot Bay, Maine, we conducted a telemetry experiment in 2005. We implanted 26 salmon smolts with ultrasonic depth tags, and monitored movement activity and fish passage with linear detection arrays through 44.2 km of the estuary and 45.5 km of the bay. During daylight in the bay, greater than 95% of the detections occurred in water depths of 5 m or less, but depths to 37 m were recorded. At night, 99% of the detections were in the top 5 m of the water column and maximum depth was 9 m. Overall survival was 39% and was highest for smaller fish and those released earlier in the smolt run, when river discharge was greater. Rapid emigration (i.e., approximately 1 km/h) and preferential surface orientation improved survival. These results verify that postsmolts are primarily surface oriented in the waters of Penobscot Bay and that they may experience high rates of nearshore mortality despite their short residence time. Detailed emigration and behavioral data such as these allow scientists and managers to delineate areas of high mortality to develop strategies that improve survival, and provide marine spatial planners information to minimize impacts of coastal zone development.