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Tracy D. Hill

Document Type

Dissertation - University Access Only

Award Date

1997

Degree Name

Doctor of Philosophy (PhD)

Department / School

Wildlife and Fisheries Science

First Advisor

Walter G. Duffy

Keywords

south dakota, lake oahe, chinook salmon

Abstract

The food habits and population dynamics of chinook salmon Oncorhynchus tshawytscha were investigated from 1993 through 1995 and was combined with information on energetics and growth from previous studies to determine the trophic interactions of chinook salmon in Lake Oahe, South Dakota. During each year of the study chinook salmon were sampled monthly from May through September and in February using experimental monofilament gill nets. Chinook salmon from 117 to 872 mm total length were sampled from the reservoir. Mean catch per unit effort (CPUE) ranged from 0.05 fish/h in February and May to 1.20 fish/h in July. Comparison of CPUE values revealed that catches differed among months (x2=.49.06, df=5, P=0.0001). Mean back-calculated length-at-age was slightly larger for males than females. A body lengthscale radius intercept for Lake Oahe chinook salmon was determined to be 59.2 mm (r2=0.96, P=0.0001). A total of 529 chinook salmon stomachs were examined for diet composition. The diet of age-0 chinook salmon consisted primarily of invertebrates when salmon were first stocked, but then changed to age-0 rainbow smelt Osmerus mordax within two months. Age-I chinook salmon relied on both age-0 and adult rainbow smelt as their primary prey; age-0 smelt contributed little to the diet of older salmon. Age-3 chinook salmon consumed only adult rainbow smelt. Life table analysis of chinook salmon collected with gill nets revealed that survival rate decreased with age. Annual survival rate estimates for Lake Oahe chinook salmon ranged from 62% for age-0 salmon to 4% for age-3 salmon. A bioenergetics model developed for chinook salmon in Lake Oahe was used to estimate predation on rainbow smelt. Modeled chinook salmon growth estimates were usually within ± 1 standard deviation of the measured monthly weights for chinook salmon collected with gill nets. Total biomass of rainbow smelt consumed by an average individual chinook salmon increased with age. Estimated mean biomass of adult rainbow smelt consumed by an average individual chinook salmon ranged from 184 g/year for age-0 salmon to 12,567 g/year for age-3 salmon. The chinook salmon in Lake Oahe consumed an estimated 1,685 metric tons of rainbow smelt in 1993, 1,640 metric tons in 1994, and 1,944 metric tons in 1995. Model simulations revealed that information collected at Whitlocks Bay Spawning Station could be used to develop bioenergetics models for Lake Oahe chinook salmon. Growth depicted by the spawning station simulation was similar to growth predicted by the baseline simulation and closely approximated the weights measured from monthly gill net samples. Bioenergetics modeling was then used to address community-level impacts of walleyes Stizostedion vitreum, chinook salmon, and rainbow trout Oncorhynchus mykiss on the rainbow smelt population in Lake Oahe. The baseline model simulation of the three predator species revealed that walleyes were responsible for 80% of the consumption of rainbow smelt in Lake Oahe in 1993. Chinook salmon were the second greatest consumers, while rainbow trout consumed the least rainbow smelt biomass. Partitioned estimates of cumulative consumption by 100, 000 stocked fish of each species revealed that chinook salmon consumed more adult and age-0 rainbow smelt than rainbow trout or walleyes. Consumption of adult rainbow smelt by chinook salmon was estimated to be 3.4 times and 5.7 times more than consumption by rainbow trout or walleyes. Accurate reservoir-wide estimates of rainbow smelt biomass are needed to increase reliability and provide greater interpretive value from the bioenergetics simulations developed for walleyes, chinook salmon, and rainbow trout. Bioenergetics models can serve as a framework for future studies on the Lake Oahe fish communiy and can be utilized to investigate ecological impacts of future management scenarios. This study demonstrated the importance of rainbow smelt in Lake Oahe as a prey resource. Management efforts should be directed at a better understanding of this prey resource to ensure the future of the Lake Oahe fisheries.

Library of Congress Subject Headings

Chinook salmon -- Oahe, Lake (S.D. and N.D.)
Bioenergetics

Description

Includes bibliographical references (page 107-118)

Format

application/pdf

Number of Pages

152

Publisher

South Dakota State University

Rights

Copyright © 1997 Tracy D. Hill. All rights reserved.

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