Experimental Test of Using Predator Traits and Prey Behavior to Predict the Vulnerability of Bighead Carp to Native Piscivores

Long-term monitoring of fish communities in the Illinois River has detected several changes in the native piscivore assemblage following large increases in the relative abundance of Bighead Carp and Silver Carp in the early 2000s. Invasive carp are capable of having large spawning events, resulting in high abundances of young of the year carp that form large, highly visible schools. The wide diversity of predation strategies employed by predators in the Illinois River, and their possible variation in effectiveness at capitalizing on this new prey resource, could be a contributing factor in the differential success of piscivore taxa following establishment of bigheaded carp. We used a trait-based approach to predict predator behaviors that are either deterred or facilitated by the schooling behavior of Bighead Carp. We have begun testing these predictions by conducting experiments that quantify the vulnerability of Bighead Carp schools to either a generalist predator that actively searches for prey (Largemouth Bass) or a specialist piscivore with an ambush strategy (Shortnose Gar). Experiments took place in mesocosm tanks and were monitored by video to quantify foraging efficiency and predator-prey behaviors potentially affecting carp vulnerability. A mechanistic understanding of which types of predatory strategies are well suited for capitalizing on the presence of large schools of juvenile bigheaded carp as potential prey will be essential for predicting and understanding post-invasion food web dynamics.