Species in the genus Epioblasma have specialized life history requirements and represent the most endangered genus of freshwater mussels (Unionidae) in the world. A genetic characterization of extant populations of the oyster mussel E. capsaeformis and tan riffleshell E. florentina walkeri sensu late was conducted to assess taxonomic validity and to resolve conservation issues for recovery planning. These mussel species exhibit pronounced phenotypic variation, but were difficult to characterize phylogenetically using DNA sequences. Monophyletic lineages, congruent with phenotypic variation among species, were obtained only after extensive analysis of combined mitochondrial (1396 bp of 16S, cytochrome- b , and ND1) and nuclear (515 bp of ITS-1) DNA sequences. In contrast, analysis of variation at 10 hypervariable DNA microsatellite loci showed moderately to highly diverged populations based on F_ST and R_ST values, which ranged from 0.12 to 0.39 and 0.15 to 0.71, respectively. Quantitative variation between species was observed in fish-host specificity, with transformation success of glochidia of E. capsaeformis significantly greater ( P <0.05) on greenside darter Etheostoma blennioides , and that of E. f. walkeri significantly greater ( P <0.05) on fantail darter Etheostoma flabellare . Lengths of glochidia differed significantly ( P <0.001) among species and populations, with mean sizes ranging from 241 to 272 µm. The texture and colour of the mantle-pad of E. capsaeformis sensu stricto is smooth and bluish-white, whereas that of E. f. walkeri is pustuled and brown, with tan mottling. Based on extensive molecular, morphological and life history data, the population of E. capsaeformis from the Duck River, Tennessee, USA is proposed as a separate species, and the population of E. f. walkeri from Indian Creek, upper Clinch River, Virginia, USA is proposed as a distinct subspecies.

Genetic variation was examined in two endangered mussel species, Epioblasma brevidens and Epioblasma capsaeformis, and in a non-listed species, Lampsi

Appropriate inference of population status for endangered species is extremely important. Using a single model for estimating population growth rates is typically inadequate for assessing endangered species because inferences based on only one “best” model ignore model uncertainty. In this study, the endangered dromedary pearlymussel ( Dromus dromas ) in the Clinch and Powell rivers of eastern Tennessee, USA, was used as an example to demonstrate the importance of multiple models, with consideration of environmental noises for evaluating population growth. Our results showed that more than one model deserves consideration in making inferences of population growth rate. A Bayesian model averaging approach was used to make inferences by weighting each model using the deviance information criterion. To test the uncertainty resulting from model selection and the efficiency of the Bayesian averaging approach, a simulation study was conducted on the dromedary pearlymussel populations, which showed that model selection uncertainty is very high. The results of these tests lead us to recommend using Bayesian model averaging to assess population growth status for endangered species, by balancing goodness-of-fit and selection uncertainty among alternate models.

In the 20th century, Pendleton Island (PI) in the Clinch River of southwestern Virginia was a singularly important location for conservation of freshwater mussels in North America, supporting at least 45 species. Comprising 55,500 m2 of available habitat, PI is the largest contiguous patch of habitat for mussels in the unregulated reaches of the Clinch River in either Virginia or Tennessee. Mussel density at PI declined by 96% from its historical baseline of 25/m2 in 1979 to ∼1/m2 in 2014, indicating a collapse of the fauna. We provide a quantitative description of the PI mussel assemblage collapse and establish baseline conditions for restoration scenarios. We examined long-term monitoring data collected at 15 sites in the Tennessee and Virginia sections of the river over a 35-yr period (1979–2014). While the mussel assemblage of PI has declined precipitously, density in the Tennessee section of the river has increased at an annual rate of 2.3% (1979–2004) and 1.3% (2004–14), stabilizing at a mean density of 29/m2 over the last 10-yr period, a reasonable baseline density to gauge recovery and restoration at PI and at other disturbed sites in the river. Lost mussel abundance can and should be translated to ecosystem services loss at PI, representing more than 1.38 million mussels and tens of millions of lost mussel service years. When density of the PI mussel assemblage is projected forward 30 yr (2014–44), it returns to a baseline of 25/m2 in 2036 only under a high-growth-rate scenario of 15% per yr. If realistic growth rate scenarios of 1% and 5% are used, density reaches 1.4/m2 (∼75,000 individuals) and 4.3/m2 (∼240,000 individuals), respectively, by 2044. These scenarios assume healthy nondegraded habitat conditions, which do not reflect current water and sediment quality at PI. Recovery of the assemblage to baseline densities will take decades and require active restoration of the fauna and habitat, including mussel translocations and stocking of hatchery-propagated juveniles.