Otolith Microstructure and Trace Elemental Analyses of Age-0 Silver Carp in the Upper Mississippi River

Silver Carp (Hypophthalmichthys molitrix) may spawn multiple times and come from multiple nurseries in a given river reach. In 2016, a high-magnitude spawning event of Silver Carp occurred near the invasion front in the Upper Mississippi River (UMR). Understanding reproduction, growth and nursery habitats can be beneficial to management. Our objectives were to determine (1) hatch dates and back-calculated growth rates from otolith microstructure and (2) nursery locations of young-of-year (YOY) Silver Carp from otolith microchemistry. We collected 12,208 YOY Silver Carp from Pools 18-19 of the UMR (16–231mm) between July 2016 to October 2016. Lapilli and asteriscii otoliths were removed, polished, and photographed. Lapilli otolith daily increments were used to calculate hatch dates and incremental distance was measured to determine daily growth. Nursery origins of YOY were determined from lapillus otolith (Sr: Ca and Ba: Ca ratios) and asteriscus otolith (stable isotope δ18O). Ages ranged from 17–112 days with corresponding hatch dates between May 22–August 14, 2016. Nursery locations were assigned to the main channel above LD19, one of several large tributaries, or small tributaries above LD19. This study demonstrates multiple spawning events and nursery sources that might contribute to recruitment.