Using Microchemistry and Stable Isotopes to Determine Early-Life Environment and Movement of the Emerging Bigheaded Carp Population in Pools 16–19 of the Mississippi River

Bigheaded carp (bighead carp and silver carp) are invasive species in the US and have spread throughout most of the Mississippi River Basin. Population abundance upstream of Lock and Dam 19 (LD19) on the Upper Mississippi River has been limited by the high head dam at this location, which restricts all upstream passage to the lock chamber. To determine early-life environment of adults captured upstream LD19 (Pools 16–19), I measured otolith (lapillus) stable isotope composition and elemental microchemistry of 150 silver carp (80 females, 70 males) and 146 bighead carp (77 females, 70 males). Otolith isotope (δ18O) and elemental ratios (Sr:Ca and Ba:Ca) were compared to values of isotope and elemental ratios from putative early-life environment water sources to assign early life history for each fish. Early-life environment sources from upstream and downstream of LD19 were evident. Most adult bighead carp collected from Pools 16–19 (66.4%) and silver carp collected from Pools 17–19 (53.3%) had otolith core chemical signatures consistent with early-life environments downstream of LD19. Nearly 12% (n = 146) of bighead carp had otolith core signatures reflective of locations upstream of LD19 and 21.9% (32/146) of bighead carp could not be classified regarding origin in relation to LD19. Proportionally, 12% (n = 150) of silver carp had otolith core signatures reflective of origins upstream of LD19 and the origin of only 6.7% (n = 150) of silver carp in relation to LD19 could not be determined. Collectively, sex ratios of bigheaded carp with early-life environments downstream of LD19 did not differ, regardless of combing pools (bighead carp: χ2 = 0.975, P = 0.61; n = 97; silver carp: χ2 =3.616, P = 0.16, n = 80). Tracking early-life environments of fish upstream LD19 through time could be used to evaluate changes of abundance upstream of LD19, change in reproductive status in a low-density population, and monitor the effectiveness of ongoing and potential control efforts implemented at LD19