The Fate of Hatchery-Spawned Atlantic Salmon Released into the Penobscot River, ME

Endangered Maine Atlantic Salmon are the focus of restoration efforts including hatchery supplementation using sea-run broodstock.  The species is iteroparous and fish are released after artificial spawning. Adults are usually returned downstream of the lowermost dam (Milford, rkm 62) into the Penobscot River estuary.  It is thought that this release location will maximize survival by avoiding dam passage.  Recovery in this tidal environment, however, may be a mismatch with behavioral tendencies.  In 2015 we sought to better characterize post-release behavior by surgically radio tagging 56 artificially spawned sea-run adults and tracking them through the following spring. To assess the survival risk imposed by Milford Dam, half of these fish were released in the estuary while half were released further upstream (rkm 91). Movements through the river were assessed using stationary radio telemetry receivers in conjunction with weekly mobile surveys.  While some released fish did leave the system in the fall, many adults remained in the system until spring. Upstream movements were common among released fish in both groups and many individuals approached dams at a time when fish passage was not in operation.  We consider these patterns and their significance for standard management practices.