Competition potential between saugers and walleyes in nonnative sympatry

Sauger Sander canadensis populations throughout North America have exhibited declines over the past few decades. Various factors may be contribute to the reduced population abundance of saugers in the middle Missouri River of Montana, including interspecific competition with walleyes Sander vitreus. We compared the seasonal migrations, habitat use, and diets of both species in the middle Missouri River to assess competition potential. Before the presumed spawning period, 96% of saugers and 57% of walleyes migrated as far as 264 kilometers downstream. After spawning, both species returned to previously occupied river reaches and demonstrated site fidelity during the nonmigratory season. Habitat use by saugers and walleyes was similar at three hierarchical spatial scales. Diet overlap was high during the spring and summer and moderate during autumn. Resource overlap of saugers and walleyes in the middle Missouri River of Montana suggests that the competition potential between these species is high, which may preclude the recovery of native sauger populations where resources are limiting.