Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Wildlife and Fisheries Science

First Advisor

Walter G. Duff


The food habits, caloric density, and population dynamics of walleye Stizostedion vitreum were determined in 1993 and 1994 and combined with information on energetics and growth to determine the trophic interactions of walleyes in Lake Oahe, South Dakota. Monofilament gill nets were set at three depths in the water column (bottom, suspended, and surface) from May through September, 1994 to determine the effect of gill net placement on catch rates of walleyes. Catch per unit effort of walleyes was greater in bottom nets during July (5.2/net-h) than any other month or net location. In addition, 25- and 38-mm mesh sizes were effective for capturing walleyes between 320 and 490 mm. High water levels and below average water temperatures allowed a cold-water prey fish, rainbow smelt Osmerus mordax, to occupy most of the water column throughout Oahe Reservoir in 1993. The fluctuating water levels and water temperatures have also had an influence on the food habits of walleyes. The relative importance (RI) index was used to compare walleye food habits in 1993 with those from a similar study of Lake Oahe conducted in 1991. Rainbow smelt had higher RI values than other prey in all regions of the reservoir during May to September, 1993. In 1991, rainbow smelt dominated the diet of walleyes only in the lower portion of the reservoir and diets were very diverse in the upper reaches. Mean seasonal caloric density of mature walleyes (~ age 3) showed distinct seasonal trends during May through September, 1994. Mean energy density was lowest during spring (1,820 cal/g) and highest during fall (1,960 cal/g). Immature walleyes (~ age-2) showed no apparent seasonal trends in mean caloric density, but values differed among months. Changes in caloric density were also observed for rainbow smelt, lake herring Coregonus artedi, yellow perch Perea flavescens, and spottail shiners Notropis hudsonius among months. Age and seasonal differences exist in the energy density of fishes, and these factors need to be considered in energetics studies. A bioenergetics model developed for walleyes in Lake Oahe was used to estimate predation on rainbow smelt, the primary forage species in the reservoir. Model estimates indicated that ages 1-6 walleyes in Lake Oahe would consume most of the rainbow smelt production, 8.639 x 109 g, over the course of one year. Potential changes in growth and consumption resulting from changing environmental conditions were then modeled. Model results suggested that growth of walleyes would increase slightly (20%) if the rainbow smelt population crashed and lake herring became established as a predominant prey species. However, growth of walleyes would decrease by as much as 50% if the rainbow smelt population declined due to an increase in water temperatures and a decrease in cold water habitat. The use of bioenergetics modeling in Lake Oahe will allow biologists to address a wide variety of problems and concerns that may affect management decisions. This study demonstrated the importance of rainbow smelt in Lake Oahe as a forage fish. Management efforts need to be directed towards understanding this prey species to ensure the future of the walleye fishery.

Library of Congress Subject Headings

Walleye (Fish)--Oahe, Lake (S.D. and N.D.)


Includes bibliographical references (pages 124-138)



Number of Pages



South Dakota State University


Copyright 2014 Scott D. Bryan. All Rights Reserved.