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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Wildlife and Fisheries Science

First Advisor

Walter G. Duffy


Rainbow trout Oncorhynchus mykiss have been stocked in Lake Oahe, South Dakota for the past 25 years. In recent years spawning runs of rainbow trout have increased, providing South Dakota Department of Game, Fish and Parks biologist the opportunity to substantially increase stocking rates. Concern exist on what effects an increase in the rainbow trout population might have on the rainbow smelt Osmerus mordax population. The objective of this study was to modify the bioenergetics model developed by Hewett and Johnson inorder to determine the total consumption of rainbow smelt by the rainbow trout population in Lake Oahe, South Dakota. Rainbow trout were sampled with monofilament gill nets set on the bottom, surface, and suspended in Lake Oahe, South Dakota during May through September, 1993 and 1994. Rainbow trout were captured with the least amount of effort during July. The 25- and 38-mm mesh sizes caught more fish than any other mesh size in all three net locations. The 38-mm mesh effectively sampled rainbow trout ranging from 300 to 455 mm. This study demonstrated that mean CPUE is influenced by net placement and mesh size of monofilament gill nets, as well as the species and length ranges of fish being sampled, and that these factors need to be considered when designing a sampling program. The food habits of rainbow trout were analyzed from Lake Oahe, South Dakota, from May through September, 1993- 1994. Diets were analyzed using the relative importance (RI) index. Composition of the diet differed among months and among length groups of rainbow trout. Greatest RI values for zooplankton prey occurred during May, July and August. Terrestrial invertebrates had the highest RI value in rainbow trout diets during June and September. Overall, RI values for aquatic macroinvertebrates and rainbow smelt were lower than the other two prey categories. Zooplankton were the most important prey for rainbow trout < 330 mm and decreased in importance as rainbow trout increased in length. Rainbow trout between 330-459 mm fed predominantly on terrestrial invertebrates. Rainbow smelt were incorporated into the diet of rainbow trout between 201-330 mm and increased in importance as rainbow trout length increased. Rainbow smelt dominated the diet of rainbow trout > 460 mm. A bioenergetics model developed for rainbow trout in Lake Oahe was used to estimate the total predation on the rainbow smelt population. Model estimates indicated that age 1-3 rainbow trout were consuming 88, 940 kg of rainbow smelt annually from May through September. This model estimate is substantially lower than the consumption estimates of rainbow smelt by walleye Stizostedion vitreum and chinook salmon Oncorhynchus tschawytscha in Lake Oahe.

Library of Congress Subject Headings

Rainbow trout -- Oahe, Lake (S.D. and N.D.)


Includes bibliographical references (page 70-79)



Number of Pages



South Dakota State University


Copyright © 1997 Sean T. Lott. All rights reserved.