Characteristics and Spatial Segregation of Sympatric Saugers and Walleyes in the Ottawa River, Canada

Abstract

Few comparative studies exist on the sympatric populations of Saugers Sander canadensis and Walleyes S. vitreus, especially in northern rivers. Depth-stratified, standardized index netting surveys were conducted in the Ottawa River, Canada—a large, fragmented northern river. The objectives of this study were to (1) determine whether Saugers and Walleyes were spatially segregated within river reaches; (2) assess whether relative abundances of the two species were correlated within river reaches and ascertain factors affecting their relative abundances; (3) determine whether life history characteristics in this northern river were within the variation reported for each species; and (4) evaluate whether there was synchrony in year-class strength between the two species and identify the factors affecting year-class strength. Saugers and Walleyes were spatially segregated, specifically by depth. Probability of capture was greatest in the 20–35-m depth stratum for Saugers and in the 6–12-m depth stratum for Walleyes. Relative abundances of Saugers and Walleyes were correlated and were positively related to reach characteristics (i.e., mean and maximum depth, reach length, and river kilometers upstream from the confluence) but negatively related to thermal conditions (i.e., growing degree-days, water temperature at preferred depths, and human population in proximity to the river). Life history characteristics were within the literature-reported ranges except for Saugers, which were older with a smaller length at 50% maturity. Year-class strengths of Saugers and Walleyes were synchronous at the reach and river levels and were positively correlated with mean annual temperature but negatively correlated with mean annual river flow. Saugers and Walleyes can coexist within large water bodies. Recruitment synchrony suggests that spawning management efforts could benefit both species, which could be advantageous when managing the Sauger, a lesser studied species. However, life history differences advocate that harvest regulations (e.g., size limits) must be species specific in order to be effective.

Received June 13, 2013; accepted January 27, 2015

ACKNOWLEDGMENTS

I thank the BSM crews from the OMNRF Pembroke and Kemptville district offices; the Laurentian Freshwater Cooperative Unit for conducting a portion the FWIN surveys; and Henri Fournier (Quebec Ministry of Natural Resources) for sharing FWIN data. Nigel Lester (OMNRF) provided insightful comments on the manuscript; Tal Dunkley (OMNRF) assisted with GIS analyses. Funding for this project was provided by the OMNRF Science and Information Division.