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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Wildlife and Fisheries Science

First Advisor

David W. Willis


Historic fish assemblages in the Black Hills of South Dakota were simple and lacked fishes that were considered sport species. Catchable (279- 381-mm) trout (Salmonidae) fisheries currently compose a large portion of the recreational fishing in Black Hills streams and reservoirs. Put-and-take fisheries are the standard management practice for Black Hills reservoirs because natural recruitment is low to non-existent. Recently, juvenile rainbow trout Oncorhynchus mykiss of unknown origin were collected in the Castle Creek tributary system above Deerfield Reservoir, indicating that natural reproduction is occurring. The purpose of this project was to evaluate the extent to which natural recruitment of rainbow trout contributed to the sport fishery in Deerfield Reservoir. Thus, the objectives of this study were to 1) evaluate the genetic origins of naturally reproduced rainbow trout in Castle Creek, South Fork Castle Creek, and Deerfield Reservoir, 2) evaluate the contribution of wild rainbow trout to the sport fishery in Castle Creek, South Fork Castle Creek, and Deerfield Reservoir, and 3) evaluate the movements of wild and stocked rainbow trout between Deerfield Reservoir and Castle and South Fork Castle creeks. To evaluate the genetic origins of naturally reproduced rainbow trout in the Deerfield Reservoir system I collected field tissue samples from hatchery-raised, harvested rainbow trout obtained through a summer creel survey and naturally reproduced rainbow trout. Tissue samples were also collected from three known genetic strains of rainbow trout (Erwin, McConaughy, and Shasta) in South Dakota Department of Game, Fish and Parks (SDGFP) operated McNenny State Fish Hatchery in Spearfish, South Dakota. Eight microsatellite markers were used to genotype rainbow trout deoxyribonucleic acid (DNA). Genotyped data were tested for conformance with Hardy-Weinberg equilibrium and linkage disequilibrium using a software package (GenePop 4.1) prior to assignment testing. Assessment of all samples was evaluated by detecting three clusters based on multiplexed genotypes. Assignment tests conducted with the software program STRUCTURE assigned each individual to a cluster, with each cluster relating to the parental source subpopulation. The three reference strains showed little admixture, indicating distinct genetic backgrounds. Assignment of naturally reproduced fish collected within the tributary system above the reservoir indicated contribution of genetic material largely from two of the three strains of rainbow trout stocked, Erwin and McConaughy. Shasta strain rainbow trout showed little or no contribution to the genetic composition of naturally reproduced fish, but were present in the harvested rainbow trout. I used scale growth characteristics to distinguish between rainbow trout of wild and hatchery origin using analysis of scale growth patterns and subsequently estimated the proportions of wild- and hatchery-origin fish that were sampled during the annual lake survey. Logistic regression analysis was used to develop a predictive model based on scale measurements for known wild and known hatchery fish. The model was highly significant (P=0.001), but rho squared was only 0.167 (i.e., rho = 0.41). Moderate overlap in scale measurements for wild and hatchery fish did occur; however, the model correctly classified 60% of the input data. The predictive logistic regression equation was then used to calculate the probability that each of the 28 unknown (i.e., unclipped) fish in the standard lake survey were of hatchery or wild origin. The calculated probability values for our 28 unknown fish ranged from 0.05 (relatively certain to be a wild fish) to 0.93 (relatively certain to be a hatchery fish); 13 were classified as wild fish and 13 as hatchery fish. Given that 50% of the Deerfield Reservoir standardized sample consisted of unknown origin rainbow trout, potentially as many as 25% of the reservoir population are of wild origin. To evaluate adfluvial movements by the three unique strains of rainbow trout currently stocked into the Deerfield Reservoir system by SDGFP, I used passive integrated transponder technology (PIT) to track movements of tagged individuals of each strain between Deerfield Reservoir and its primary tributary system, Castle Creek. Two thousand and ninety-four rainbow trout were implanted with PIT tags in McNenny State Fish Hatchery (known strain) or on site (unknown strain or wild) within either Deerfield Reservoir or the Castle Creek tributary system; movements were continuously recorded from August 2010 to August 2011. Of the 2,094 tagged rainbow trout, 159 (8%) were detected entering the Castle Creek system. Pair-wise chi-square tests between combinations of all strains at all segments revealed that significant differences in movement existed; McConaughy strain fish exhibited the highest proportion of tagged individuals moving upstream followed by Erwin and Shasta strains, respectively. Additionally, pair-wise comparisons between strains revealed that significant differences (P=0.05) existed in upstream movements among all three strains into three upstream segments. The highest numbers of tagged individuals detected were McConaughy strain rainbow trout in all cases. Knowledge of the origins of the naturally reproduced rainbow trout as well as the ability of these naturally reproducing fish to contribute to the sport fishery is essential to apply the best management strategy. If a put-and-take fishery is desired, current management strategies are likely sufficient to provide a consistent fishery consisting of hatchery-raised, catchable-sized rainbow trout. To promote a more self-sustaining fishery, current management likely needs to change. A reduction in the overall number of hatchery-raised rainbow trout stocked into the system would likely help reduce detrimental effects of hatchery raised rainbow trout on the naturally recruiting rainbow trout population. Additionally, stocking strains that are likely to naturalize to the system could increase natural recruitment within the reservoir system.

Library of Congress Subject Headings

Rainbow trout--South Dakota--Deerfield Reservoir
Rainbow trout--South Dakota--Deerfield Reservoir--Reproduction
Fish populations--South Dakota--Deerfield Reservoir


Includes bibliographical references (pages 93-109)



Number of Pages



South Dakota State University


Copyright © 1996. Jacob L. Davis. All rights reserved.