Reproductive biology and comparative growth rates of selected species of freshwater mussels (Bivalvia: Unionidae) in the New and Greenbrier Rivers, Virginia and West Virginia

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Virginia Polytechnic Institute and State University

The reproductive biology of four unionid mussels, Actinonaias carinata, Elliptio dilatata, Cyclonaias tuberculata, and Tritogonia verrucosa, from the New River in Virginia and West Virginia was investigated. The gametogenic cycle, length and timing of spawning and glochidial release periods, and age at sexual maturity were described for each species. Comparisons of growth rates of C. tuberculata subpopulations from the Greenbrier River and three locations downstream of Bluestone Dam on the New River in West Virginia were also made to determine the effect of the dam on growth of mussels downstream.

A. carinata is bradytictic, spawning in mid-summer, brooding glochidia throughout the fall and winter, and releasing them in the spring. E. dilatata, C. tuberculata, and T. verrucosa are tachytictic. Spawning began in mid-March for these three species and continued into May for T. verrucosa, into June for C. tuberculata, and into July for E. dilatata. Glochidia were released upon maturation, beginning in mid-April and continuing through June for T. verrucosa, and into August for E. dilatata. C. tuberculata released glochidia from March through June. All four species appeared to reach sexual maturity between the ages of 4 and 6, depending upon the species.

Growth in shell length in the four subpopulations of C. tuberculata was asymptotic. Growth rate, described by the parameter w from a reparameterization of the von Bertalanffy growth equation, was significantly higher immediately below Bluestone Dam compared to the site furthest downstream. Growth of this species did not differ significantly among the other sites; however, a trend of decreasing growth rate with increasing distance from the dam was apparent. Observed differences in growth were attributed to differences in food availability and quality resulting from the operation of Bluestone Dam.