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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Wildlife and Fisheries Science

First Advisor

Walter G. Duffy


Rainbow smelt Osmerus mordax were introduced into Lake Oahe, South Dakota, in the 1970's. I studied rainbow smelt and zooplankton interactions in Lake Oahe during 1990 to evaluate the influence of rainbow smelt predation on the zooplankton community. Zooplankton composition and abundance and the diet of adult rainbow smelt were determined at three stations. Digestion rates of zooplankton consumed by adult rainbow smelt were measured in the laboratory. I compared zooplankton abundance and community composition data collected in 1990 with data collected in 1969, 1986, and 1987 to determine if any changes in the zooplankton community have occurred since the introduction of rainbow smelt in Lake Oahe. The diet of adult rainbow smelt was dominated by cladocerans and also included low numbers of copepods and chironomid larvae and pupae. Adult rainbow smelt selected Daphnia pulex over other prey at all sampling stations. Other species positively selected for were Daphnia galeata mendotae and Leptodora kindtii. Rainbow smelt prey were significantly larger than mean size of zooplankton in the environment. Zooplankton densities ranged from 254/L at Whitlock's Channel in May to 10/L at Bush's Bay in June. Cyclopoid copepods were numerically dominant at all sampling stations, composing 38% to 54% of the organisms identified. Calanoid copepods and cladocerans were also common. Densities of cladocerans, cyclopoid copepods, and rotifers at Whitlock's Bay and Whitlock's Channel were greater than densities at Bush's Bay, Bush's Channel, and Spring Creek Channel. Calanoid copepod density was greatest at Spring Creek Channel. Zooplankton densities in the top depth stratum were less than in either the middle or bottom strata. Rotifer density peaked in early June. Cladoceran and cyclopoid copepod densities were greatest in mid June. Calanoid copepod density reached its maximum in early July. I found the zooplankton community in 1990 was similar to the community that existed in 1969. Observed shifts in species abundance could not be attributed to size-selective predation by rainbow smelt. Digestion rates of adult rainbow smelt were measured at water temperatures of 2.5, 5.0, 8.0, 12.0, and 16.0°C. The highest rate (0.363 mg/h) occurred at 12.0°c. At 2.5°c digestion rate was low (0.026 mg/h) and changed little over time. At temperatures of 5.0, 8.0, 12.0 and 16.0°c, digestion rates decreased over time in a negative exponential manner, with the greatest decline between O and 2 h. Gastric evacuation was complete after 8 h at 5.0°C, 13. 5 h at 8. 0 and 12. 0°C, and 4 h at 16. 0°C. At 2.5°C, gastric evacuation was calculated to be complete approximately 50 h after ingestion. Percentage of rainbow smelt feeding increased with water temperature. Predicted maximum consumption occurred at 10.1°C. These data will be incorporated into a bioenergetics model for rainbow smelt inhabiting Lake Oahe, South Dakota.

Library of Congress Subject Headings

Smelts -- South Dakota -- Oahe, Lake -- Feeding and feeds
Zooplankton -- South Dakota -- Oahe, Lake -- Composition


Includes biliographical references(page 102-105)



Number of Pages



South Dakota State University


Copyright © 1992 Kim S. Karnitz. All rights reserved.