Assessing the probability of grass carp (Ctenopharyngodon idella) spawning in the Sandusky River using discharge and water temperature

Grass carp (Ctenopharyngodon idella, Val.) is an invasive species in the Laurentian Great Lakes region with the potential for damaging the lake ecosystem and harming the region's economy. Grass carp spawning was documented in the Sandusky River, Ohio, in 2015 through targeted egg sampling. Continued egg sampling in the Sandusky River suggested that grass carp spawning is related to discharge and water temperature. We used egg sampling data from 2014 to 2021 to develop a Bayesian model to understand the likely conditions related to grass carp spawning in the Lake Erie watershed. The resulting model estimates the likelihood of spawning as a function of discharge and water temperature. The results suggest that spawning is most likely to occur when discharge is above 10 m³/s and water temperature is below 25 ℃. The model provides a tool for setting research and management priorities to develop management strategies to reduce the grass carp population in Lake Erie. Furthermore, the Bayesian nature of the model makes the model updatable when new data are available, whether from the same river or from another river, to incorporate river-specific features to identify likely spawning rivers.