Using Otolith Chemistry to Determine Early Life Environments and Movement of the Emerging Bigheaded Carp Population in Pools 16–19 of the Upper Mississippi River.

This article focuses on determining the early life environments (ELEs) of invasive bigheaded carp—Silver Carp (Hypophthalmichthys molitrix) and Bighead Carp (H. nobilis)—captured upstream of Lock and Dam 19 (LD19) on the upper Mississippi River (UMR) to inform management strategies. Using otolith stable isotope (δ18O) and elemental (Sr:Ca, Ba:Ca) analyses of 287 adult carp collected from Pools 16–19, the study found that most individuals originated from ELEs downstream of LD19, indicating that the high-head dam limits upstream recruitment but does not completely prevent upstream passage. Approximately 11–12% of carp had ELEs upstream of LD19, suggesting localized reproduction above the dam, though this proportion has remained stable over time. The sex ratios of carp passing upstream were balanced, and the findings support continued use of LD19 as a control point, with removal efforts downstream and deterrents at the lock potentially effective in limiting upstream spread.