Midwest Fish & Wildlife Conference 2018

AUTHORS. Jesse A. Williams, Western Illinois University; Jim T. Lamer, Western Illinois University; Gregory W. Whitledge, Southern Illinois University-Carbondale; Brent Knights, Upper Midwest Environmental Sciences Center-United States Geological Survey; Nick Bloomfield, United States Fish and Wildlife Service-La Crosse

ABSTRACT. Silver carp (Hypophthalmichthys molitrix) are capable of spawning multiple times a yearin relation with increased water velocity and water temperature. Asian carp recently had a large, unprecedented spawning event in the Upper Mississippi River (UMR) where densities of adults are low compared to other regions of the Basin. It is not known how environmental conditions influence daily growth of juvenile silver carp in the UMR; or their natal environments in this recently invaded system. Understanding growth and spatial life history can be beneficial to the management of silver carp. Our objectives are to (1) determine hatch date and back-calculated growth in relation to temperature and hydrology and (2) determine natal origin and subsequent spatial distributions of young of year silver carp using stable isotope otolith microchemistry. We collected 475 juveniles from Pools 18-19 of the UMR that range from 16–231mm between July 2016 to October 2016. Samples were collected using seines, trawls, electrofishing, and electro-seines. Lapillus and asteriscus otoliths were removed, polished, and photographed. Polished otoliths were analyzed to calculate hatch dates from incremental (daily) growth depositions. The annuli widths were measured to determine daily growth as correlated with daily water temperature and hydrology. Natal origins and spatial life history of the silver carp were determined from lapillus otolith microchemistry (Sr: Ca and Ba: Ca ratios), while the asteriscus otoliths were prepared for stable isotope (d18O). Horton Creek samples from July 15, 2016 had birthdates from June 14, 2016 and samples from September 23, 2016 had birthdates from July 23, 2016 indicating multiple cohorts. The two collection dates had hatch groupings that varied, demonstrating multiple, mass spawning events.