Genetic effects of habitat fragmentation on blue sucker populations in the upper Missouri River (Cycleptus elongatus Lesueur, 1918)

Abstract

The blue sucker, Cycleptus elongatus, is a large catostomid fish that occurs in main stem rivers throughout the Mississippi basin of North America. Although not federally listed as threatened or endangered, populations are not considered stable in any of 21 states where they occur. Included in the range is the Missouri River, which flows more than 3,200 km from Montana to St. Louis, Missouri. Historically, C. elongatus was distributed con- tinuously throughout the main stem Missouri and its major tributaries, but from 1952 to 1963, six major impound- ments were constructed on the upper Missouri by the US Army Corps of Engineers. The resulting reservoirs have inundated and fragmented large riverine habitat from Yankton, South Dakota to the headwaters. C. elongatus still occurs in remnant stretches between reservoirs; how- ever, little is known of the impacts of the dams on these populations. In order to test for such effects, 231 individ- uals from nine sites were genotyped at 14 variable microsatellite loci. An additional 142 individuals from six sites in the Mississippi River were also genotyped for comparative purposes. In the Missouri, allelic richness was reduced in inter-reservoir sites relative to those in the free flowing lower river. In addition, significant isolation by distance occurs in the Missouri, a pattern not present in the unimpounded Mississippi. These results are consistent with reduced intradrainage gene flow in the Missouri River and are the first to indicate effects of impoundments on genetic structure in the system. This information will assist gov- erning agencies in making informed decisions regarding conservation of C. elongatus in the Missouri River drain- age and throughout the range.