A secondary upstream invasion of round goby in the Great Lakes Basin over fourteen years following a dam removal.

Dam removal projects are increasingly used restoration approaches to support fish migration and freshwater biodiversity. Unfortunately, improved watershed connectivity can promote the spread of invasive species. The Rouge River (Michigan, USA), a Great Lakes Area of Concern, is a degraded ecosystem undergoing ongoing restoration and improvement. To evaluate tradeoffs between restoration benefits and invasion risk, we examined the spread of invasive round goby, Neogobius melanostomus, over 14 years (2012-2025) following the removal of the Wayne Road Dam in the Rouge River watershed. Using community fish data collected through a participatory science program run by Friends of the Rouge, we found round goby traveled approximately 23 river kilometers upstream, with an average speed of 1.9 river km/year. Invasion speed peaked in downstream sites with a maximum speed of 9.3 river km/year. Within sites, increases in round goby relative abundance slowed over time. Across sites, relative abundance of round goby was best predicted by johnny darter relative abundance (Etheostoma nigrum), modeled July water temperature, abundance of gravel substrate, Time Since Invasion (TSI), and baseflow. The relative abundance of johnny darter, a small benthic fish with similar traits to round goby, was related to the abundance of cobble and gravel substrate, baseflow, TSI, and round goby relative abundance. Our findings illustrate the complex responses that can emerge when restoration efforts such as dam removals occur in freshwater ecosystems that are often simultaneously facing the spread and impact of invasive species.