Potential Beneficial Effects of Invasive Silver Carp on Native Fishes

Substantial research attests to the injurious impacts invasive silver carp (Hypophthalmichthys molotrix) have on Midwestern U.S. river systems. Particularly, the dietary overlap between silver carp and native planktivores has resulted in declined condition and abundance of these species in areas where silver carp dominate the community (i.e., the lower Illinois River). However, additional research demonstrates silver carp may benefit native non-planktivorous fishes because of the carp’s ability to produce young at a large scale providing an abundant prey source for native piscivores, and their nutrient rich fecal pellets may enrich benthic forage quality for native benthivores. Potential positive effects of silver carp for native fishes are not fully understood, and research is limited in natural systems. Here we determine whether silver carp benefit non-planktivorous native fishes in the lower Illinois River (i.e., Peoria, LaGrange, and Alton pools) by examining native piscivore and benthivore body condition over time utilizing two standardized long-term data programs. We found a significant positive relationship between silver carp abundance and native benthivore body condition. Moreover, visual trends indicate increased body condition during and immediately after strong silver carp year classes (2008 & 2014) for both native piscivores and benthivores. Therefore density-dependent effects may exist where juvenile silver carp populations and benthic nutrient levels must reach a threshold before they are exploitable (i.e., beneficial) resources. We suggest more years of data that incorporate strong silver carp year classes may be needed to clarify potential positive effects of silver carp for native non-planktivorous fishes.