Assessing the Influence of Imprinting and Stocking Timing on Atlantic Salmon Smolt to Adult Return

Supplementation using hatchery Atlantic Salmon smolts is an important conservation strategy for the recovery of this endangered fish in the Penobscot River, Maine.  During downstream migration, smolts can incur significant direct or indirect mortality from dams and predation.  Survival at seawater entry has also been shown to vary with many factors including fish physiology and environmental conditions. As a result, when and where fish are stocked can be critical considerations for success.  We investigated two methods of stocking, each being carried out for 3 consecutive years. For the first method, smolts were acclimated in upstream “imprinting pools” before being trucked and directly released into the estuary on an outgoing tide (n=30,000).  Control fish (n=90,000) were released upstream of the lowermost dams (2009-2012).  For the second method, daytime releases below the lowermost dam was compared with nighttime releases (2014-2016; 45,000 for each group). All fish were marked with VIE tags to identify treatment groups.  Adult returns as 1, 2 and 3 year adults are compared.  Data suggest that the first stocking strategy did not influence smolt to adult survival.  The first year’s results will be considered for the day v. nighttime release strategy.