Modelling grass carp egg transport using a 3-D hydrodynamic river model: the role of egg retention in dead zones on spawning success

Invasive grass carp (Ctenopharyngodon idella) are known to spawn in the Sandusky River, Ohio, USA, within the Great Lakes Basin, and are threatening to expand throughout the Great Lakes. Successful spawning is thought to require that eggs remain in suspension until hatching, which depends on river hydrodynamics and temperature-dependent egg development. Previous modelling efforts used one-dimensional hydrodynamic models that simplify egg movement by not simulating low-velocity zones within the river. To examine the effect of low-velocity zones on egg transit times and hatching rates, we developed a novel coupling of a biophysical Lagrangian particle tracker and three-dimensional hydrodynamic model on the Sandusky River during a high-flow event. The model successfully predicted egg-capture data for a range of developmental stages and revealed a mechanism that resuspends eggs trapped in low-velocity zones. The resuspension mechanism increases the residence time of grass carp eggs in spawning tributaries and can lead to successful hatching occurring in shorter distances than previously estimated. Grass carp potentially spawning in shorter tributary lengths has widespread implications for efforts preventing establishment in the Great Lakes Basin.

Does the value of newly accessible spawning habitat for walleye (Stizostedion vitreum) depend on its location relative to nursery habitats?

The benefit accrued from habitat restoration actions may depend not only on the quality and quantity of habitat restored, but also on its location relative to other critical habitats. For example, walleye (Stizostedion vitreum) larvae need to be transported by river currents from spawning to nursery habitats soon after emergence. We developed a model of river transport survival for larval walleye to evaluate potential recruitment from riverine spawning habitats to lacustrine nursery areas. Published relationships were used to model transport survival as a function of temperature and velocity. At greater distances from nursery areas, mortality risk increases, particularly as a result of starvation at relatively high river temperatures. We applied the model to the Sandusky River, a tributary to western Lake Erie, and found potential larval production from spawning habitat above an existing dam to exceed the potential of presently accessible spawning areas by a factor of 8. We used a generalized version of the model to show that for transport distances of less than 100 km, transport survival is much more sensitive to variations in river flows, whereas at greater distances, temperature becomes increasingly important.