Diet Analysis of Predatory Fish in Pools 19 and 20 of the Upper Mississippi River with Contrasting Habitats and Asian Carp Abundance

The geographic range of silver (Hypophthalmichthys molotrix) and bighead carp (H. nobilis) has expanded in the Upper Mississippi River. Lock and Dam 19, a significant high-head dam on the UMR, serves as a potential pinch point for Asian carp. Lock and Dam 19 separates vastly different hydrogeomorphic areas in Pool 19 and Pool 20. Pool 19 is characterized by lentic conditions with high abundances of aquatic vegetation and macro-invertebrates, whereas Pool 20 generally lacks lacustrine habitat and associated macrophytes and fauna. Due to the opportunistic nature of predatory fishes, dietary differences are expected between these variable habitats. Also, if larval or juvenile Asian carp occur in these areas, predation on them by native piscivore fishes would be expected. This study examined predatory fish diets in Pools 19 and 20 to determine if significant dietary differences exist between pools including reliance on available larval or juvenile Asian carp. Specimens were captured using PDC boat electrofishing at random sites from 15 June to 31 October 2013 and 2014. Using visual techniques, diets were quantified and compared. Genetic barcoding was used to identify fish tissue to species when necessary. Our data showed significant dietary differences in the abundance of snails (Gastropoda), caddisfly larvae (Trichoptera), water boatmen (Coryxidae), midge larvae (Chironomidae), mayfly larvae (Ephemeroptera), and forage fish (Notropis spp. and Dorosoma cepedianum) between Pools 19 and 20 among species. Only one Asian carp was found in a diet (Pool 20) suggesting little or no Asian carp spawning or recruitment occurred in these areas or these predators did not prey on larval or juvenile Asian carp during the sampling time frame. Diets should be quantified in future years within this reach as the Asian carp geographic range expands further upstream.