Assessing Walleye Movement among Reaches of a Large, Fragmented River

Movement of Walleyes Sander vitreus among reaches in a large, fragmented river was assessed by employing a combination of tagging, telemetry, and genetic analyses. Our objective was to determine whether the existing dams in the Ottawa River, Canada, were impeding Walleye movement among river reaches. Movement was predicted to be greater among contiguous, unimpounded reaches in comparison with impounded reaches. In total, 1,586 Walleyes were tagged in five river reaches, and 35 Walleyes were tracked by radiotelemetry in three river reaches. Genetic analyses (linkage disequilibrium, genetic divergence and diversity, effective population size, genetic structuring, bottlenecks, and migration rates) were conducted on 221 Walleyes from seven river reaches by genotyping at six microsatellite loci. Based on both tag returns (return rate = 12.1%) and telemetry data, there was limited movement among river reaches whether impounded or unimpounded, and movement was predominately upstream. Genetic analyses identified population structuring, with three genetic groupings occurring within the river. There was also evidence of genetic isolation in an upper reach of the river, indicating potential residual effects of a bottleneck or genetic drift. Our results suggest that existing dams may not act as significant barriers to Walleye movement in the Ottawa River, but limited movements appear to maintain genetic diversity and minimize genetic drift. Consequently, maintaining the genetic attributes of Walleye stocks in segmented rivers may require some level of fish passage. Received July 9, 2012; accepted January 16, 2015