- Holbrook, Christopher Michael
University of Maine Graduate School
Acoustic telemetry was used to evaluate passage success, survival and behavior of migrating Atlantic salmon (Salmo salar), at both the smolt and adult stages, through the Penobscot River and Estuary, Maine. Survival and behavior of migrating hatchery (n=493) and naturally-reared (n=133) smolts were evaluated in 2005 and 2006. Mortality, movement rates, and use of a secondary migration path (the Stillwater Branch) were quantified, and related to rearing, release history, and migratory condition (gill Na*,K*-ATPase activity and condition factor). River sections containing three mainstem dams (Howland, Milford and West Enfield dams) accounted for 43% and 60% of total losses for 2005 and 2006, respectively, though these sections accounted for only 16% and 6% of monitored reaches. Survivorships through individual sections with dams ranged from 95- 100% and 71-100% in 2005 and 2006, respectively. Movement rates were significantly slower at dams compared to free-flowing reaches, and smolts arriving at dams during the day experienced longer delays than smolts arriving at night. Hatchery smolts released in April were not ready to migrate at time of release, but migrated earlier than wild smolts in both years. Gill Na*,K*-ATPase activity was positively associated with movement rate to the estuary in both years. Further, gill Na*,K*-ATPase activity for wild smolts was similar to hatchery smolts that were released 29-26 days earlier in 2005 and 2006, respectively. Hatchery smolts released in May showed similar freshwater survival compared to both wild smolts and hatchery smolts released in April, but behavior was more similar to wild smolts than earlier-released hatchery smolts. Use of the Stillwater Branch by individual release groups ranged from 0-26% and 0-19% in 2005 and 2006, respectively, and was positively related to discharge. Smolts released in the Pleasant River at Milo used the Stillwater Branch at a significantly lower rate than smolts released in the mainstem. These results indicate that fundamental differences exist between hatchery and naturally reared smolts, and may help mangers determine which rearing and release protocols best meet the goals of the restoration program.