Unionidae (bivalvia) of the Arkansas River System of SE Kansas and SW Missouri: species of concern, historical change, commercial harvest, and sampling methods.

Abstract

Freshwater mussel assemblages were examined at 99 sites between 1993 and 1995 in the Arkansas River System of southeast Kansas and southwest Missouri. Emphasis was placed on five mussel species that are candidates for adding to the federal list of threatened and endangered species. These species are the Neosho mucket (Lampsilis rafinesqueana), Ouachita kidneyshell (Ptychobranchus occidentalis), western fanshell (Cyprogenia aberti), rabbitsfoot (Quadrola cylindrica), and elktoe (Alasmidonta marginata). I also evaluated (i) historical change ofmussel assemblages in southeast Kansas, (ii) the effectiveness ofa mussel harvest refuge located on the Neosho River, and (iii) differences in sampling results between quantitative and qualitative methods. From a total of 15,068 mussels of35 species, I caught 1421 candidate mussels, viz., 1301 L. rafinesqueana, 83 P. occidentalis, 29 C. aberti, seven Q. cylindrica, and one A. marginata. Habitat utilized by these species was principally shallow riffles and runs. Relatively silt-free and moderately compacted gravel was the most utilized substratum. Disparity between species represented by extant specimens and species represented by weathered valves revealed a significant decrease in species richness in several Kansas streams. My findings also indicated substantial range reductions in Kansas, with many populations small and isolated, and consisting of mostly aged individuals. I also evaluated the Neosho River mussel harvest refuge, located from the Neosho Falls dam, Woodson County, downstream 6.1 km to the confluence ofRock Creek, Allen County. Eight sites were selected, four within and four outside refuge boundaries, and were sampled quantitatively during summer 1994. Forty 1_m2 quadrats were chosen randomly at each site within a 10 X 100 m area of riffle habitat, with 10-15 em of substrate excavated from each quadrat. From these sites, 744 mussels of20 species were caught, including 11 species on the Kansas list of threatened and endangered species. Three harvestable species, Amblema plicata, Quadrula metanevra, and Quadrula quadrula, failed to show significant differences in the percentage of legal-sized specimens between refuge and non-refuge sites. Moreover, unionid densities and species richness were generally lower at refuge sites. However, shell length of Q. metanevra was significantly greater at refuge versus non-refuge sites, and two species legally harvestable through 1991 also yielded significantly larger specimens at refuge sites. Finally, I compared quadrat samples with timed snorkel searches in describing unionid community structure at nine Neosho River sites. At each site, snorkel searches were employed in a 10 x 100 m stretch. Following identification and sizing, mussels were returned to their original location, and 40 1_m2 quadrat samples were taken from the same stretch. A total of 786 mussels was caught from over 12 h of snorkel searches, and 896 from 360 1_m2 quadrats. Evaluations of species diversity and relative abundance were not significantly different between methods; however, snorkel searches revealed significantly fewer species, and were less effective in detecting small mussels.