Multi-state models of downstream migrating Atlantic salmon smolts in the Penobscot River

The Penobscot River hosts the largest return of adult Atlantic salmon in the U.S., but runs are very low compared historic numbers.  Stocking of hatchery reared smolts is a major restoration tool but has had only moderate success in recent years.  Previous acoustic telemetry studies have shown that downstream passage success is variable among years and sites. We used acoustic telemetry, with over 40 arrays and 640 acoustically tagged smolts, to quantify downstream passage success, survival and movement into the Gulf of Maine in 2009 and 2010.  We used multi-state models in Program MARK to assess the survival and path choice for two upriver freshwater stocking locations and a single direct estuary release.  Two areas had high apparent loss included a heavily dammed section accounting for up to 20% loss and the estuary and bay which for account for 10-30% loss.  Our best fit models compare reaches with and without dams demonstrate the high loss of dam influenced sections.  Path choice through the estuary and bay are variable and linked to release site.