Diet breadth and variability in Sander spp. inferred from stable isotopes

We used stable isotopes of carbon and nitrogen to evaluate trophic similarity between sauger Sander canadensis and walleye S. vitreus in three Missouri River impoundments characterized by unique differences in riverine habitat. Mean δ¹⁵N was similar for sauger and walleye in each reservoir ranging from 15.7 to 17.8‰ for sauger and 15.2 to 17.7‰ for walleye. However, mean δ¹³C was greater for sauger (−24‰) than for walleye (−25‰) in Lake Oahe (lacustrine habitat), where rainbow smelt Osmerus mordax is an important prey species for walleye. Variation in δ¹⁵N and δ¹³C values was similar between walleye and sauger in Lewis and Clark Lake (riverine habitat), but was greater for sauger than for walleye in Lake Oahe, implying that in pelagic environments, sauger exhibit a larger diet breadth and lower diet consistency compared with walleyes. Isotope analyses support observations from traditional gut content studies that diet overlap between sauger and walleye varies with environmental conditions and is more similar in riverine food webs than in large lakes and impoundments.