How Changes in Passage Efficiency of Alewife at Main Stem Dams Can Influence Nutrient Dynamics in the St. Croix River, ME

Three fish-ways at main-stem dams on the St. Croix River had been closed to diadromous fish passage since the late 1980s by the State of Maine.  Collaboration between State, national, and First Nations participants led to the reopening of these fish-ways in 2013, allowing migratory fish access to historic spawning grounds.  Alewife were once present in large numbers in the St. Croix watershed and are anticipated to increase in response to increased habitat access.  Alewives can act as a nutrient source during migration through carcasses, gametes, and excretion and this spring pulse is part of the nutrient budget of intact coastal systems.  A heuristic model was developed to assess how changes in passage efficiency at the three dams on the St. Croix River might influence the population dynamics of alewife and, in turn, how distribution of nutrients in the watershed might be affected.  The model will be used to address questions of improved passage as well as determining how an increase in alewife presence could influence the net flow of nutrients in the St. Croix River.  Model development will be described, and multiple scenarios will be addressed using realistic reallocation scenarios.