Evaluating changes in diadromous species distributions and habitat accessibility following the Penobscot River restoration project

The Penobscot River Restoration Project (PRRP) is a multimillion-dollar endeavor that aims to restore native sea-run fish through the removal of two mainstem dams and improved fish passage at a third dam on the Penobscot River. We used geographic information systems (GIS) to quantify changes in species distribution and habitat accessibility 11 diadromous species in the Penobscot Basin following the PRRP.  Using previously compiled accounts of historic range, barrier survey data, and simulated barrier passage data, we modeled species-specific distributions and river access for all eleven species following the proposed dam removals and compared these against the current ranges and accessibility.  For some species such as Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus), the PRRP will provide access to 100% of their historic freshwater habitat.  However for other species such as alewives (Alosa pseudoharengus), approximately 66% historic spawning and rearing habitat will remain inaccessible due to the presence of other passage barriers.  These results demonstrate that the PRRP is an important step toward ecosystem recovery in the Penobscot Basin, but other restoration activities will be needed in order to realize the full potential of the PRRP.