Examining Fish Assemblage Response to Dam Removal.

Macpherson, Callista*, Kathrine M. Abbott, Allison H. Roy, U.S Geological Survey, Massachusetts Cooperative Fish and Wildlife Research Unit, University of Massachusetts Amherst, Amherst, MA

Massachusetts has over 3,000 dams, many of which are unmanaged or no longer serving their original purpose. Small run-of-river dams alter streams physically, chemically, and biologically. Dam removals have the potential to improve habitat connectivity and restore stream ecosystem structure and function. While dam removals are becoming more prevalent, the impacts on resident fish assemblages and their relationship to changes in wetland habitats following dam removals are not well understood. In this study, we examine how stream fish assemblages respond to dam removal through time using backpack electrofishing data collected by the Massachusetts Division of Fisheries and Wildlife from 1998 to 2021. We collected field data including visual stream assessments and water quality measurements. Additionally, we delineated wetlands from remotely sensed images before and after dam removal to understand the links between vegetation change and fish assemblages. A repeated measures Analysis of Variance (ANOVA) will be used to understand change over time in wetland areas and fish assemblages following dam removal across sites. Quantifying changes in upstream fish assemblages can provide insights into how habitat connectivity influences fishes, while assessing changes downstream may contribute to an understanding of the impact of dam removals on the structure and function of streams. Resource managers may use this information to better understand the biological response to dam removals and inform restoration decisions.