Abstract
Walleye Sander vitreus (Mitchill) and sauger Sander canadensis (Griffith & Smith) may occupy similar niches in sympatric populations, but their long‐term resource use is poorly studied. Multi‐tissue (liver, muscle and bone) isotopic niche analyses were used to compare resource use by these species in two large reservoirs in Saskatchewan, Canada. Population isotopic niches were larger for sauger (1.73‰ 2 –3.60‰ 2 ) than walleye (0.51‰ 2 –2.61‰ 2 ) in Lake Diefenbaker, but opposite in Tobin Lake (sauger = 0.54‰ 2 –2.57‰ 2 ; walleye = 1.30‰ 2 –2.94‰ 2 ). Analyses of population overlap suggest that these species co‐exist via niche partitioning, but partitioning was more pronounced in Lake Diefenbaker (overlap = 6%–38%; Tobin Lake overlap = 18%–62%). The size of individual niches and levels of intra‐ and interspecific overlap among individual fish also varied with reservoir. This study shows that walleye and sauger use different resources across different time scales, but the degree of partitioning can vary markedly with environment.