Fore- and Back-Casting Recruitment Potential of Grass Carp in the Sandusky River Using Known Recruitment Events

Grass Carp (Ctenopharyngodon idella) spawned in the Sandusky River, a major tributary to western Lake Erie, in 2011, 2013, and 2015. Direct evidence was observed in 2015 when eggs were collected on five different dates during three different high-flow events. Indirect evidence for the 2011 and 2013 events was inferred by collection of age-1.5 diploid individuals in 2012 (confirmed by otolith microchemistry) and an age-2 diploid in 2015. We simulated the unsteady hydraulic characteristics of the lower Sandusky River in 2011 and 2013 during similar magnitude high-flow events as the 2015 spawning (4560-13000 cubic feet/second). Results from hydraulic simulations were used together with the Fluvial Egg Drift Simulator (FluEgg) model to project likely hatching locations for the 2011 and 2013 spawning events. Results of simulated egg and larvae dispersal following the 2011 and 2013 spawning events were analyzed with the goal of evaluating optimal temperature and hydrologic conditions for recruitment success. Although this effort is focused on the Sandusky River, our analysis framework is applicable to any river system where researchers need to assess risk of spawning and recruitment of riverine spawning species.