AUTHORS: Alexis L. Gerber; Daniel Roth; Robert Colombo; Eden Effert-Fanta
ABSTRACT: Annual variation in hydrological conditions affects reproduction of riverine species uniquely, with certain taxa relying on flood pulses for successful spawning. Invasive bigheaded carp (Hypophthalmichthys spp.), are widely known for their rapid population growth and significant ecological impacts on freshwater ecosystems and native fish assemblages. Previous literature has found invasive bigheaded carp reproduction to be dependent on multiple environmental cues, such as discharge and temperature, for spawning. Discharge specifically is an essential component for bigheaded carp reproduction because their eggs require suspension in the water for proper development. Native fish species have varying spawning strategies, and many utilize similar environmental cues as invasive bigheaded carp. This study aims to evaluate the spatial and temporal variation of hydrological effects on reproduction of invasive bigheaded carp and native fish species in the lower Wabash River and its tributaries. Ichthyoplankton push nets and water quality measurements were recorded from April-September 2021-2024 at several tributary confluence sites on the lower Wabash River, which borders Illinois and Indiana. Push net samples were collected within the tributary, at the confluence site, and in the mainstem river both above and below the confluence. Environmental conditions (e.g., discharge and temperature) varied substantially within and among each season of ichthyoplankton sampling. Variation in hydrological conditions among years had a significant impact on total larval fish production. In 2021, a year with multiple high discharge events 240,106 larvae were collected, while in 2023, a year with fewer spikes in discharge only 4,300 larvae were sampled. Although invasive carp have been informally observed to congregate in high numbers within mainstem-tributary confluences, relatively little research has been conducted to analyze the roles of confluences in spawning of both invasive and native fishes. Understanding the long-term trends in hydrological variation and the spatial preferences of invasive fish communities may offer key insights into control methods and factors that influence larval native fish assemblages.
