Recruitment sources of invasive Bighead carp (Hypopthalmichthys nobilis) and Silver carp (H-molitrix) inhabiting the Illinois River

摘要

Knowledge of natal environments and dispersal of invasive Bighead carp (Hypopthalmichthys nobilis) and Silver carp (H. molitrix) inhabiting the Illinois River would be valuable for directing population reduction efforts intended to supplement electrical barriers in the Chicago Sanitary and Ship Canal and limit the probability of these species invading the Great Lakes. However, the extent to which Bighead carp and Silver carp (collectively referred to as bigheaded carps) stocks in the Illinois River are derived from recruits that originate within the Illinois River itself versus immigrants from the Mississippi and Missouri rivers is unknown. Bigheaded carps are also known to use connected floodplain lakes during early life, but the contribution of these habitats to recruitment of Bighead and Silver carps in the Illinois River is also unknown. The aim of this study was to identify natal environment of adult bigheaded carps collected from the Illinois River during 2010-2011 using stable isotope and trace element analyses of otolith cores. Both water and otolith strontium:calcium ratios (Sr:Ca) and water and otolith oxygen isotope ratios (expressed as delta O-18) were strongly correlated for known-origin bigheaded carps, consistent with other fish species. Most Bighead and Silver carps collected from the Illinois River used river channel rather than floodplain lake habitats during early life. The majority of adult Silver carp originated in the Illinois River, although 11-39 % were immigrants from the Missouri or middle Mississippi Rivers. In contrast, 97 % of the Bighead carp originated in the Illinois River. Our results indicate that efforts to substantially reduce abundance of bigheaded carps in the Illinois River drainage should continue to focus on the Illinois River itself, but will likely need to be expanded to include the middle Mississippi and Missouri Rivers for sustainable control of Silver carp.