Invasive carps in the Emiquon Preserve: a summary of the story so far

Although the EmiquonPreserve is disconnected from the lower Illinois River, it experienced multiple connections prior to the completion of the water control structure in 2016. Of particular note, record flooding in 2013 and near record flooding in 2015 and 2016 overtopped levees and brought in river water, riverine fish species, and potentially invasive carps. Although it is widely known that common carp Cyprinus carpiosurvived removal efforts prior to restoration, it was unknown if bighead carp, Hypophthalmichthys nobilis, silver carp H. molitrix, or grass carp Ctenopharyngodon idellawere present in Emiquon until 2016 when the first silver carp was documented. Since 2016, more silver carp have been observed and collected, prompting additional research questions into their status, paths of entry, and abundance within Emiquon. To address these questions, Illinois River Biological Station staff implemented additional netting in the fall of 2018. This effort led to the first documentation of bighead and grass carps as well as the collection of higher than expected numbers of all carp species. In the fall of 2019, additional gill netting and a mark-recapture study were implemented with the goal of estimating the population sizes of invasive carps within Emiquon. Results show silver, grass and common carps are larger than neighboring Illinois River carps, and the combined population of silver and bighead carps is estimated at 156,060 ± 88, 506 (95% confidence interval) individuals. Our objective here is to summarize our findings to date on invasive carps within the Emiquon Preserve.