Influence of Channel Morphology and Flow Regime On Larval Drift of Missouri River Pallid Sturgeon

The transition from drifting free embryo to exogenously feeding larvae has been identified as a potential life stage bottleneck for the endangered Missouri River pallid sturgeon. Previous studies have indicated that river regulation and fragmentation may contribute to mortality of larval pallid sturgeon by reducing the extent of free-flowing river that free embryos require to complete ontogenetic development. Calculations of total drift distance based on mean velocity, however, do not address the potential for complex channels and flow patterns to increase retention or longitudinal dispersion of free embryos. We describe the effects of different styles of channel morphology on larval dispersion and consider the implications of flow regime modifications on retention of free embryos within the Lower Missouri River. We use a one-dimensional advection-dispersion model to estimate total drift distance and employ the longitudinal dispersion coefficient as a measure to quantify the tendency towards dispersion or retention of drifting matter. The results demonstrate the complex interactions of flow regime and channel morphology and the implications of resulting hydraulic patterns on drift of free embryos. Our results also indicate that passively drifting pallid sturgeon free embryos could be exported from the Lower Missouri River into the Mississippi River.