Dam Removal Allows Re-Colonization of Historic Habitat by Three Species of Anadromous Fish in Sedgeunkedunk Stream, Maine

Historic declines of Atlantic salmon (Salmo salar) are largely attributable to the construction of dams, over-fishing, and pollution.  Over contemporary timescales, populations throughout the Northwest Atlantic have been generally declining since the early 1990s as marine survival rates have diminished sharply.  Atlantic salmon research and management programs have historically taken a single-species approach.  Recently, we have begun to pursue a new direction for research and management of the last remnant stocks of Atlantic salmon in the US by developing and testing a suite of hypotheses that link the demographic patterns of Atlantic salmon to the co-evolved suite of diadromous fishes.  These inter-species hypotheses include habitat conditioning by sea lamprey (Petromyzon marinus); predation buffer by river herring (Alosa aestivalis and Alosa pseudoharengus); marine-derived nutrient deposition by many species; and juvenile river herring and rainbow smelt (Osmerus mordax) serving as a diversified prey base.  Most of these linkages, however, remain untested hypotheses.  The putative conservation benefit of dam removal also remains an untested hypothesis as it relates to Atlantic salmon recovery.  In Sedgeunkedunk Stream, Maine, two dam removals have offered the potential for the full suite of species to naturally recover.  In many other instances, stocking has been pursued as a more active restoration approach following improvements to fish passage.  However, we have taken a different approach in Sedgeunkedunk Stream and allowed for natural recolonization.  Since the removal of the lowermost dam (Brewer Dam) in 2009, we have already seen evidence of natural recolonization by Atlantic salmon, river herring, and sea lamprey.  As we monitor ecological response to these dam removals in Sedgeunkedunk, we are able to concurrently test some inter-species hypotheses and evaluate the pace of natural recolonization.  Thus, Sedgeunkedunk Stream serves as an ideal testing ground for a number of these hypotheses that may result in a paradigm shift in Atlantic salmon research and management in the US.  A multi-species approach not only offers new pathways to successful salmon recovery but also the opportunity to provide meaningful conservation benefit to many diadromous species whose demographic status is nearly as dire as Atlantic salmon.