Hydrodynamic modeling of the upper Niagara River to assess aquatic connectivity of the emerald shiner (Notropis atherinoides) population
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Anthropogenic modifications at the head of the Niagara River attributed to land reclamation and the installation of seawalls have altered the river channel, leading to increased water velocities and reduced availability of aquatic habitat. As a result of the increased velocities, concerns have been raised that habitat connectivity of the emerald shiner (Notropis atherinoides), a key forage species for sport fish 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 connectivity was assessed by identifying hydrodynamic barriers to upstream fish movement. Using a 2-D hydrodynamic model, velocities in the river were simulated for the 10 th , 50 th and 90 th annual percentile water levels. For each simulation, the locations of potential barriers to movement were evaluated using a least-cost path analysis, swim curve theory outlined in Brett (1964), and the results of three swim tests performed on the emerald shiner by other authors. Results indicate several distinct patterns. First, large velocities immediately downstream of the Peace Bridge crossing (in excess of 2.0 m s -1 ) restrict emerald shiner movement to within close proximity of either shoreline. Second, several potential barriers exist along both the U.S. and Canadian shorelines, the largest of which were located along the vertical seawalls on either side of the river. The extent of each identified potential barrier fluctuated slightly with water level, but the location generally remained consistent. Finally, a comparison of the model results to field measurements of water velocity taken in close proximity of both shorelines shows that of the barriers identified at the scale of the model, the seawall along Broderick Park is the most substantial impediment to upstream movement, as velocities close to the shoreline remain in excess of shiner swimming ability for nearly 200 meters. Future work including empirical estimates of passage success and swimming tests on shiners native to the Niagara River will help determine if remediation work is warranted to facilitate upstream passage at the identified impediments.