AUTHORS: Braden Whisler, Eastern Illinois University; Robert Colombo, Eastern Illinois University; Daniel Roth, Eastern Illinois University; Eden Effert-Fanta, Eastern Illinois University
ABSTRACT: Bighead Carp (Hypophtalmichtys nobilis) and Silver Carp (H. molitrix), often referred to as bigheaded carps (BHC), have invaded many rivers throughout North America and the Mississippi River drainage. With their niche occupation and feeding habits, evidence suggests the degradation of native fish assemblages through competition. Although there are spawning populations located throughout the BHC invasion, few studies have focused on visualizing the timing and location of spawning events. The aim of this study is to examine how spawning BHC utilize tributary versus mainstem river sites throughout the year and in varying environmental conditions. From April to September of 2021-2024, BHC ichthyoplankton were collected from mainstem and tributary sites in the La Grange Pool of the Illinois River throughout an array of different environmental conditions (flood, high/low stream velocity, temperature). Consistent with previous studies, flood pulses, higher water velocities, and temperature thresholds triggered spawning events, contributing to higher densities of BHC ichthyoplankton drifting in the current. High-water years also facilitated the movement of BHC into tributary systems, contributing to spawning events and larger BHC ichthyoplankton catches in the tributaries. This study demonstrates the importance of continued monitoring of spawning conditions and timing in areas where BHC are already established. By developing predictive models for BHC spawning events in both mainstem and tributary habitats, resource managers can implement targeted removal strategies for spawning adults at invasion fronts or areas of special concern, such as the Laurentian Great Lakes. These proactive measures have the potential to significantly reduce year class sizes and mitigate the ecological impact of BHC invasions.
