Use of Molecular Techniques to Confirm Nonnative Fish Predation on Razorback Sucker Larvae in Lake Mohave, Arizona and Nevada

Larval predation by nonnative fishes has long been implicated in the decline of western native large-river fishes, but visual assessment of predation is difficult due to the postconsumption degradation of fragile larvae. Molecular techniques were used to demonstrate predation on the larvae of endangered Razorback Suckers Xyrauchen texanus by nonnative juvenile centrarchids in field samples from Lake Mohave, Arizona–Nevada, where larvae are seasonally abundant. Razorback Sucker DNA was detected in the gut contents of 7% and 9% of Bluegills Lepomis macrochirus and in 14% and 15% of Green Sunfish L. cyanellus that were captured during spring 2014 and 2015, respectively. There was no significant (α = 0.05) effect of predator TL, predator species, or year on the presence of larval DNA. Juvenile centrarchids have the potential to consume substantial numbers of Razorback Sucker larvae and thus to impact recruitment. The control of nonnative fishes may be impractical, but a viable alternative for mitigation of their impacts is to provide nonnative-free refugia for native large-river fishes. Received June 17, 2016; accepted September 19, 2016 Published online January 19, 2017