Survey of Freshwater Mussels (Bivalvia: Unionoidea) in Three River Drainages and an Evaluation of Seasonal Flow Requirements as a Correlate of Mussel Recruitment

The status of freshwater mussels (Bivalvia: Unionoidea) has declined over the last 30 years such that they are one of the most imperiled taxonomic groups in North America. Mussel populations in Kansas have followed a similar trend of decline. To better understand the status of mussels in the state, Kansas Department of Wildlife and Parks has established a monitoring program in which 10 river basins containing “high priority mussel communities will be surveyed every six years. I surveyed mussels on three rivers in eastern Kansas during the summers of 2003 and 2004: Marais des Cygnes River, Fall River, and Grouse Creek. To achieve quantifiable, repeatable survey data, 40 1-m [squared] quadrats were searched randomly for mussels at each site. Using 1,010 quadrats, I sampled 26 sites among the three rivers and encountered 4,522 mussels (density = 4.5 mussels per m[squared]) and 25 species. I also conducted timed searches at each site to better understand community structure and to increase the probability of locating rare species that might not be encountered in the quadrat survey. In 28 timed searches, I collected 2,522 mussels (CPUE = 42.3 mussels per person-hour) comprising 25 species. Chapter 2 Recruitment is the number of individuals surviving to a defined size or age. One factor in the decline of some mussel populations is the lack of recruitment of mussels beyond their first year. Several factors have been postulated as sources of reduced recruitment, including altered stream water temperatures, altered flow regimes and temperatures as a result of reservoir releases, and natural seasonal flow variability. Previous studies have suggested that at least some period of low flow late in the breeding season is necessary so juvenile mussels are not flushed out of the immediate system before they settle into a mussel bed. I designed a study to examine the relationship of flow patterns in two rivers in eastern Kansas, Fall River and Marais des Cygnes River, during the May through August breeding season of three species of mussels (Obliquaria reflexa, Quadrula pustulosa, and Fusconaia flava) in order to assess their recruitment success. I used a thin-sectioning technique to prepare mussel valves for aging internal annuli. I sectioned and aged 98 O. reflexa, 110 Q. pustulosa, and 56 F.flava valves. From the age data, I constructed recruitment-frequency histograms to show the years that each individual was recruited. I added hydrographs for the appropriate rivers to the recruitment-frequency histograms and explored patterns of flow that were associated with successful recruitment years. Using the Indicators of Hydrologic Alteration (IHA) program produced by The Nature Conservancy, I compared median monthly flows for recruitment years versus non-recruitment years. Mussels from the Fall River site showed significantly lower flows late in the breeding season of recruitment years compared to non-recruitment years. Marais des Cygnes samples did not show significantly different patterns of flow for recruitment years versus non-recruitment years. Understanding the requirements of successful recruitment of mussels is all important step in formulating future management efforts to conserve declining mussel populations