Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Natural Resource Management

First Advisor

Nels H. Troelstrup


freshwater mussels, South Dakota, survey, Unionidae


Native freshwater mussels (Family: Unionidae) are among the most threatened groups of freshwater fauna on Earth. Approximately 35 species have gone extinct since the 1900s and 72% of remaining species are considered endangered, threatened, or species of special concern. Unionid research can begin by establishing species presence and distributions via surveys. Objectives for this study were to 1) implement the first comprehensive unionid survey for South Dakota to assess distribution, composition, and decline, 2) estimate assemblage density and determine local versus broad scale habitat drivers of assemblage variation, and 3) determine areas of unionid conservation priority in South Dakota. Mussels were qualitatively sampled in 2014 and 2015 from wadable and perennial streams at 202 randomly generated sites proportionately distributed throughout 14 major river basins in South Dakota. We found a total of 1152 individuals and 15 unique species with significant differences in richness and abundance between eastern and western halves of the state. Of the 202 survey sites, 91 showed evidence of unionids and 44 sites had live mussels. At sites where live mussels were encountered (n=44), quantitative adaptive cluster sampling was conducted during 2016 to estimate population densities and environmental drivers of assemblage variation. Average density was found to be 0.05 mussels m-2. Non-metric multidimensional scaling was utilized to evaluate and estimate local, in-stream versus broad scale habitat drivers of assemblage variation of the 44 quantitatively sampled sites. Silt, fine gravel, sand, current velocity, and conductivity were significant in driving the assemblages. Fish hosts were found not to limit mussel distributions, instead, widespread land conversions to cultivated crop agriculture may be influencing assemblage distributions. Priority conservation areas were determined via a previously published ranking system. Conservation priority analysis of sites revealed conservation and management efforts would be most useful if focused in basins east of the Missouri River as the most abundant, rich, and diverse assemblages occur there. Most of the sites were found to overlap with Conservation Opportunity Areas defined by South Dakota Fish, Game & Parks. Collectively throughout the 2014-2016 surveys, we encountered 17 species, which was a 53% decline from the 36 species surveyed historically in South Dakota.

Library of Congress Subject Headings

Freshwater mussels -- South Dakota.

Freshwater mussels -- Habitat -- South Dakota.



Includes bibliographical references (pages 74-91)



Number of Pages



South Dakota State University



Rights Statement

In Copyright