Ecosystem response to large-scale barrier removal on the Penobscot River, Maine

Removal of a number of significant migration barriers on the Penobscot River, Maine will have implications for restoration for anadromous Atlantic salmon, alosid and other native diadromous species presently surviving as relict populations. Two hydroelectric dams in the lower river will be removed, and enhanced fish passage will be provided at two additional dams.  Shifts in mesohabitat structure, habitat connectivity, predator-prey relations, and re-influx of marine nutrients are expected to include  re-structuring of riverine fish communities. This paper describes a multi-year monitoring study of the pre- and post-project fish community, and how IBI metrics will be adopted to index the ecological changes.  A total of 20 stations were established throughout the lower 40 miles of the mainstem and on six major tributaries. Each site was surveyed annually during June and September to document seasonal changes in fish assemblage structure due to reproduction and migration.  Reaches of the river presently inhabited by anadromous species were surveyed more frequently to better document the transient spring migrations. The study establishes a quantitative pre-project baseline throughout key segments of the river and provides a template so that ongoing monitoring after the physical restoration is completed can measure the ecological response.