Minnow trap styles and baiting strategies on round goby (Neogobius melanostomus) capture rates: Lessons from a complex invasion front

The round goby (Neogobius melanostomus) invaded the Great Lakes in the 1990s and the species continued expansion into inland bodies of water, raising basin wide concerns for negative ecological impacts. The Lower Fox River (LFR), Wisconsin, USA, is the state's largest tributary linking the Great Lakes to inland Lake Winnebago through a fragmented waterway of eight lock and dam structures across 62.0 river kilometers (RKm). Round goby were detected in the LFR lower river reaches, in the early 2000's below an invasive species barrier (completely sealed structure) located near the midpoint of the LFR (RKm 31.5), but in 2015, the species was observed above the barrier raising concerns for upstream invasion. This discovery prompted the closure of the upper most navigational lock system (Menasha Lock, RKm 62.0) separating the outflow of Lake Winnebago to the LFR. The goal of this study was to assess the distribution and abundance of round goby throughout the entire LFR in 2019-2021 using baited minnow traps. We further evaluate differences in capture rates between combinations of minnow trap styles, bait types, and bait quantities. A total of 1,007 round goby were captured during monitoring surveys throughout the LFR (2019-2021), confirming presence in all river segments with maximum upstream extent reaching Menasha Lock. Highest densities of round goby are found below the invasive species barrier (RKm 31.5), but males and females are present at the current maximum upstream distribution. An additional 834 round goby were captured during the comparison of trapping strategies and suggest round-style minnow traps baited with food (i.e., dog food or hotdog) are successful in capturing round goby and outperform other trap/bait types. Continued monitoring would help describe trends in abundance and adaptive sampling approaches will improve detection.