AbstractConcern has been increasing over the impacts of incidental catches of river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis) in commercial fisheries for Atlantic Herring Clupea harengus and Atlantic Mackerel Scomber scombrus, but historical information on mixed-species catches and their driving factors is lacking. We examined data from spring and fall bottom trawl surveys (National Oceanic and Atmospheric Administration, Northeast Fisheries Science Center) for temporal trends in overlap and potential ecosystem drivers of overlap trends. Species overlap changed substantially over time, with changes varying by season and region of the northeastern U.S. continental shelf. In the fall, changes in overlap were positively related to abundance in Georges Bank and southern New England. In the spring, most changes in species overlap were positively related to increasing species abundances. Positive relationships between overlap and abundance suggested that as species distributions ...