American shad in the Penobscot River: Choosing recovery tools

The planned restoration efforts in the Penobscot River include the removal of two main-stem dams (48 and 60 rkm) and the improvements of passage at the lowest remaining dam, Milford (rkm 62).  Shad are present in the Penobscot River, though presumed to be few in number, fueling concerns that unaided recovery could either fail or be protracted after access to upriver habitat is restored.  Stocking has been proposed to accelerate recovery, though cost, ecological impacts and risk to local population structure are undercharacterized.  In order to assess the theoretical benefits of stocking, we built a deterministic population model using existing size, fecundity, iteroparity and intrinsic population growth data.  As expected the base model was very sensitive to initial population size and stocking.  Stocking of the proposed 12 million fry, presuming an initial 1,000 shad and population that stabilizes at ~600K, would advance the time to reaching a stabilized population by about 15 years.  The greatest impact of stocking is at low population size.  This same time to population stability is reached assuming the initial population size is 5,000.  It is hoped that this heuristic exercise may inform decisions associate with the cost and benefit of stocking over an extant population.