Juvenile Silver Carp and Bighead Carp as Forage for Predatory Fish in the LaGrange Reach of the Illinois River

Abstract

AbstractIncreasing numbers of Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis (commonly called “bigheaded carp”) in the Illinois River have led to concerns about the impact that their invasion has on native food web dynamics. Bigheaded Carp recruited in large numbers in the LaGrange Reach of the Illinois River during the summer of 2014. This provided an opportunity to determine whether native piscivorous fish prey upon invasive carp when they are abundant. Using electrofishing and fyke nets in the LaGrange Reach (August 1–November 8, 2014), we sampled native predatory fish (n = 1,472) for stomach content analysis. Fish community data from the Upper Mississippi River Restoration Program’s Long‐Term Resource Monitoring was used to quantify prey abundance (fish < 100 mm) in the study area and indicated that bigheaded carp represented 9% of available prey. Stomach content analysis revealed that the frequency of occurrence of juvenile bigheaded carp was greater than 15% in Shortnose Gar Lepisosteus platostomus, White Bass Morone chrysops, Black Crappie Pomoxis nigromaculatus, Channel Catfish Ictalurus punctatus, Smallmouth Bass Micropterus dolomieu, Largemouth Bass Micropterus salmoides, White Crappie Pomoxis annularis, Yellow Perch Perca flavescens, Flathead Catfish Pylodictis olivaris, Freshwater Drum Aplodinotus grunniens, and Yellow Bass Morone mississippiensis. Predators sampled in August and September foraged more heavily on juvenile bigheaded carp than those sampled in October and November. Electivity analysis suggested that juvenile bigheaded carp were selected over native forage by White Bass, Black Crappie, and Shortnose Gar, as these predators continued consuming them even as availability declined. Our results imply that native piscivores in the Illinois River consume and sometimes prefer juvenile bigheaded carp as prey. These results suggest that native predators might play a role in regulating bigheaded carp recruitment and that negative impacts to predators in areas of dense carp populations might be somewhat mitigated by the consumption of juvenile bigheaded carp.