Using Bioenergetics to Estimate Consumption of Stocked Age‐0 Walleye by a Suite of Piscivores

Abstract

AbstractAge‐0 Walleye Sander vitreus are stocked throughout North America to maintain and supplement populations. Predation has been implicated as a factor limiting survival of stocked age‐0 Walleye; however, the timing, duration, and extent of poststocking predation remains uncertain. Our objectives were to estimate the abundance of predators in areas adjacent to stocking locations, estimate temporal variation in the proportion of stocked age‐0 Walleye (98–287 mm) in predator diets, and estimate the total proportion of stocked age‐0 Walleye that were consumed. The diets of Largemouth Bass Micropterus salmoides, Northern Pike Esox lucius, and adult Walleye were examined in East Okoboji and West Okoboji lakes, Iowa, before and after age‐0 Walleye stocking, and bioenergetics models were used to estimate the number of age‐0 Walleye consumed from stocking through ice‐up. During both years, Largemouth Bass had the highest densities in West Okoboji Lake, whereas densities of all other predators were similar in East Okoboji Lake. The highest proportions of age‐0 Walleye in predator diets (up to 1.0) generally occurred within 14 d after the most recent stocking event, with the proportion of age‐0 Walleye in predator diets decreasing thereafter. Northern Pike had the highest proportion of age‐0 Walleye in their diets (mean ± SD = 0.12 ± 0.32 age‐0 Walleye/individual) followed by Largemouth Bass (0.11 ± 0.30 age‐0 Walleye/individual) and adult Walleye (0.04 ± 0.20 age‐0 Walleye/individual). At the end of 2016, the estimated proportion of age‐0 Walleye consumed was 0.15 ± 0.08 (95% CI) in East Okoboji Lake and 0.29 ± 0.13 in West Okoboji Lake. At the end of 2017, the estimated proportion of age‐0 Walleye consumed was 0.47 ± 0.16 in East Okoboji Lake and 0.64 ± 0.02 in West Okoboji Lake. Overall, predators consumed large proportions of stocked Walleye, suggesting that alternative stocking practices should be considered.