Environmental factors associated with silver carp presence and relative abundance near an invasion front to inform removal efforts

Management of invasive fishes has relied heavily upon understanding their spatial distributions and habitat use at fine spatial scales to guide treatments and removals. In the USA, targeted removal is used in management of bigheaded carps ( Hypophthalmichthys spp.) in the Mississippi River system to reduce invasion potential into the Laurentian Great Lakes from the upper Illinois Waterway. Our study tested factors linked to fine-scale spatial distributions of the most prevalent bigheaded carp species—silver carp ( Hypophthalmichthys molitrix )—in the upper Illinois River to increase effectiveness of removal efforts. Bi-monthly mobile hydroacoustic sampling was conducted from 2017 to 2018 and paired with continuous environmental data collection in the two northern-most invaded reaches of the upper Illinois River. Model selection was used to describe habitat conditions associated with silver carp presence and density. Depth was the most consistent predictor of silver carp presence and density, with shallower depths consistently associated with higher abundance. During summer months, shallow areas in large backwater habitats with lower temperature and higher dissolved oxygen concentration held more silver carp. These results may help managers focus targeted removal efforts through time, increase harvest effectiveness, and reduce the potential for further invasion toward the Laurentian Great Lakes.