Spatiotemporal reproduction and larval habitat associations of nonnative silver carp and bighead carp.
The establishment of nonnative Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis (collectively referred to as "bigheaded carp") in the central United States may have negative ecological consequences and economic impacts. Our objectives were to quantify patterns and habitat associations of adult bigheaded carp reproduction, larval production, and habitat use; such information is important for control strategies and identifying recruitment sources. During May-August 2011, we sampled adults and larvae at 10 sites distributed adjacent to and within the main channel of the Mississippi River at Pool 26 (study area=28 river kilometers). Female reproductive status, adult location, and larval density were compared to environmental conditions, including temperature, site velocity, and turbidity. Large females spawned earlier than their smaller counterparts. No clear spawning aggregations of adults were observed, suggesting plasticity in staging habitat. Larvae were distributed across all sites during flooding. Larval density was positively related to velocity and turbidity, suggesting that nondepositional areas may facilitate recruitment. Bigheaded carp larvae comprised 10% of the ichthyofauna. Although pooled reaches are a source of recruitment for bigheaded carp in the Mississippi River system, the low densities of bigheaded carp larvae relative to native larvae cannot explain the dominance of adults in this system. Our findings provide insights into the plastic nature of bigheaded carp reproduction and habitats associated with larval development. Control efforts that target large adult females should be conducted earlier during the spring spawn. To maintain fishing pressure, such control efforts would likely need to continue through the summer, when smaller individuals spawn, discharge decreases, and CPUE increases. However, we found no specific mass staging area or habitat type where adult females could be targeted.