Potential barriers to upstream fish passage caused by anthropogenic river modifications: A computer modeling study of emerald shiners (Notropis atherinoides) in the upper Niagara River

Anthropogenic modifications at the head of the Niagara River attributed to land reclamation and the installation of vertical, bulkhead seawalls have altered the river channel, leading to increased water velocities and reduced availability of aquatic habitat. As a result of the increased velocities in the channel, concerns have been raised that the habitat connectivity of the emerald shiner (Notropis atherinoides), a key forage species for sportfish and threatened avian species, has been reduced between Lake Erie and the upper Niagara River. In this study, the influence of water velocity stressors on emerald shiner movement was assessed by identifying potential hydrodynamic barriers to upstream fish movement using a combination of depth-averaged velocities simulated in a 2-D hydrodynamic model and field measurements collected with a current meter. Results indicate that high velocities (in excess of 2.0 m s−1) immediately downstream of the Peace Bridge, an international road crossing between Buffalo, NY, USA and Fort Erie, Ontario, Canada, restrict potential emerald shiner movement to within close proximity of either shoreline. Along both shorelines, several additional threats to successful upstream passage exist, the largest of which are located along vertical bulkhead seawalls. The extent of the identified potential barriers fluctuates slightly with water level, but the locations remain consistent. Finally, of the potential barriers identified using the model, the field measurements indicate the seawall along Broderick Park, along the U.S. shoreline, is the most substantial impediment to upstream movement, as velocities within several shiner body-lengths of the shoreline remain between 0.83 and 1.18 m s−1 for nearly 200 m. The results of this study, in conjunction with empirical estimates of passage success, swimming tests on shiners native to the Niagara River, and additional field measurements will help determine if remediation work is warranted to facilitate upstream passage at the identified impediments.