Otolith microchemistry and microstructure of age-0 silver carp for determining early-life environments and spawning periodicity in the Upper Mississippi River in 2016

In 2016, for the first time, an abundance of age-0 silver carp (Hypophthalmichthys molitrix) were captured at several sites upstream of Lock and Dam 19 on the Upper Mississippi River near Keokuk, Iowa. These data were collected in an attempt to determine the early life environments and frequency and timing of the reproductive events that led to a large year class of age-0 silver carp. This information is important for informing decisions about control measures. We sampled these fish to determine age (days) and early life environments using their otoliths. Sampled age-0 silver carp were collected from navigation Pools 18 and 19 from July–October 2016 using a variety of sampling gears. We aged these fish by counting daily growth rings on otoliths and used age estimates to determine the timing and frequency of spawning events. Hatch dates were determined from ageing lapilli otoliths from 190 age-0 Silver Carp (16–231 mm). We conducted chemical analyses on the lapilli and asteriscus otoliths from 124 of these silver carp (64–231 mm total length) to determine their early-life environments based on Sr:Ca; Br:Ca, and δ18O of the otoliths. Early-life environments were determined from the otolith microchemistry by using published relations between otolith chemistry and water chemistry of probable early life environments. Water chemistry data was collected as part of other studies and is pending publication on ScienceBase https://doi.org/10.5066/P9CLPG40. A manuscript that incorporates these data is currently in peer review at a scientific journal.