Unionid Fauna within a Selected Reach
of the Coosa River, Alabama

Jeffrey J. Herod ¹, Holly Blalock-Herod ¹, Nikki J. Kernaghan ¹, D. Shane Ruessler ¹, James D. Williams ¹, Timothy S. Gross ¹, and J. Malcolm Pierson ²

¹U.S. Geological Survey, 7920 NW 71^st Street, Gainesville, FL 32653
²Alabama Power Company, P.O. Box 2641, Birmingham, AL 35291

Abstract

The unionid fauna within a 30 km reach of the old Coosa River channel between the Weiss Reservoir spillway dam and the Weiss hydropower dam, Cherokee and Etowah counties, Alabama, was examined using qualitative and quantitative techniques. Species composition was qualitatively determined at 12 locations within the river reach. At four of these sites, quantitative techniques were used to determine species composition, estimate species densities, and assess baseline population characteristics. A preliminary glycogen analysis for an endemic species, Amblema elliottii, was conducted at the four sites to provide a baseline health assessment. Twenty species were found in the qualitative searches, including two federally listed species: Lampsilis altilis and Pleurobema decisum.  Thirteen species were found in the quadrat samples: including P. decisum.  Recent recruitment was documented for several species.  Glycogen levels varied significantly among the four sites.  Extent of species ranges varied within this reach of the Coosa River.

Methods

Our survey incorporated both qualitative and quantitative methods for species detection and densities. Qualitative searches were used to collect data for species presence and distribution. This method allowed us to determine species presence and select sites for quantitative collection in a relatively rapid fashion. Quantitative measures of density were determined at four sites. The four sites were located at approximately mid-reach of the Dead River (Figure. 1).  Quantitative sites were based on the upper and lower range where Pleurobema decisum was detected, as well as, 1 site each representing the highest and lowest relative abundance of Pleurobema decisum.

Two field crews searched the upper and lower reaches of the Dead River. The field crew at the lower reach used motorboats to move upstream. At the upper reach, field crew utilized canoes to float downstream.  The crew surveyed the river from below the Weiss spillway dam downstream to Davis Ferry, which encompasses 19 River Miles. We chose 12 sites within the river approximately 3 miles apart to wade and snorkel. Additionally, divers sampled several sites at the lower reach. At each site, we conduct timed searches and spent no less than five person hours searching for mussels. Also, basic stream parameters (eg. water temperature, dissolved oxygen, pH, turbidity, sediment type, average depth) were recorded at each quantitative site. These data could be compared to water quality data maintained by the Alabama Power Company. All mussels were identified to species, enumerated, coded as live or shell, and data recorded.

Density of Pleurobema decisum was measured at four sites, 1) the site identified during the survey as having the greatest qualitative density (catch per unit effort) of P. decisum, 2) the upper limit where P. decisum were present in the Dead River, 3) the lower limit where P. decisum were present in the Dead River and 4) medium density site.  Density of P. decisum was determined using five transects evenly placed across the width of the river channel. Each transect was 100 m long and placed parallel to orientation of the river. Every 10 meters along transect, a 1 m² quadrat was placed on the substrate and hand searched.  A total of 50 m² was searched at each of the four selected sites.

All live mussels from quadrat samples were measured in the field and replaced without harm at the collection site.  All shell material was collected under Federal Permit SA 98-16. Voucher specimens of fresh dead shell material were retained at the US Geological Survey, Biological Resources Division, Florida Integrated Science Center (FISC) for further analysis and then given to the Florida Museum of Natural History. A subset of voucher shells was deposited at the North Carolina Museum of Natural History. Voucher specimens for gastropods were taken for SARI.

Shell morphometric parameters were used from quantitative sites to establish size demographical based data sets for all species encountered during quantitative samples.   For all unionids shell length, width, height, and whole wet weight were measured in the field and the animals replaced unharmed. Dry shell weights were only measured for dead P. decisum.  Length, width, and height were measured to the nearest millimeter (mm) with Mitutoyo - Absolute Digimatic digital calipers.  Length is defined as the greatest distance from the anterior to the posterior margin of the shell.  Width is measured across the umbones at the widest part.  Height is measured as the greatest distance from the umbo to the ventral shell margin.  Dry shell weight and whole wet weight were measured to the nearest 0.1 g on an Ohaus electronic scale. Age was determined by counting external concentric bands.

Results of Quantitative Sampling

Results of Qualitative Sampling