Long-term trends in CPUE and relative weight of six fish species in the Wabash River, USA, prior to and following silver carp invasion

Silver carp (Hypophthalmichthys molitrix) dispersed to the Wabash River, Indiana in the mid-1990s. These fish compete with native, filter-feeding fish species in other central US rivers but relatively little information is available for impacts in the Wabash River. We collected fishes by boat electrofisher on the Wabash River as part of a long-term study. Abundances of six Wabash River species varied temporally, and three had stronger relationships with year than the other species: common carp (Cyprinus carpio) decreased before and after silver carp introduction, freshwater drum (Aplodinotus grunniens) increased prior to silver carp introduction, and gizzard shad (Dorosoma cepedianum) decreased before silver carp introduction. Silver carp abundance was significantly correlated only with abundance of gizzard shad. Nonmetric multidimensional scaling analysis of long-term Wabash River fish assemblages resulted in distinctive temporal and spatial patterns. Silver carp abundance increased from zero in the early 1990s to 28 individuals/km in recent years. Gizzard shad declined to low abundance simultaneous to silver carp increases, yet we did not detect significant patterns for silver carp with other Wabash River fishes.