Determining the Ecological Consequences from Historical Damming of New England Watersheds

Anadromous river herring, collectively alewives and blueback herring, were historically abundant in most northeastern U.S. coastal river systems. Dam construction, which disrupted diadromous fish migration pathways, is considered the earliest principal cause of reduced productivity and population declines. Using published surveys, GIS layers and historical documents, a database of dams constructed throughout New England watersheds from 1600-present was developed for the purposes of estimating a timeline of lost access to river herring spawning sites as a proxy for abundance. Historical accounts of migration range of river herring were used to determine total lake and stream habitat loss as a result of watershed fragmentation. Techniques have been adapted from past research focused in Maine but expanded to account for a more comprehensive view and will incorporate new information regarding freshwater productivity. The results will be used to evaluate current management and the consequences of providing access to spawning habitat through restoration on ecosystem processes, in particular predatory marine species. We demonstrate that the historical decline in commercial and recreational fish harvest can be directly attributed to the construction of dams in New England.