Influence of life-history variation on demographic responses of three freshwater mussel species (Bivalvia: Unionidae) in the Clinch River, USA

1. Variation in age, shell growth, and demographic responses of two endangered mussel species, Epioblasma brevidens and Epioblasma capsaeformis, and a third non-listed species, Lampsilis fasciola, were studied from 2004-2008 in a 32-km reach of the Clinch River, TN. 2. Observed maximum age and length of E. brevidens was 28 yr and 71.5 mm for males and 15 yr and 56.6 mm for females; of E. capsaeformis, 12 yr and 54.6 mm for males and 9 yr and 48.6 mm for females; and of L. fasciola, 45 yr and 91.3 mm for males and 24 yr and 79.8 mm for females. 3. Estimated population size was similar to 46 000 individuals for E. brevidens, similar to 862 000 individuals for E. capsaeformis, and similar to 33 000 individuals for L. fasciola. 4. Mean recruitment per year of 1 yr-olds ranged from 12.0% to 24.0% for E. brevidens, 4.2% to 56.6% for E. capsaeformis, and 10.0% to 38.5% for L. fasciola, and mean annual population growth rate was 21.0%, 31.3%, and -24.3%, respectively. 5. Juveniles were detectable but temporally and spatially variable in occurrence, and a significant proportion of the age-class structure of each species. Recruitment was exceptionally high for E. capsaeformis during years when discharge was low in spring and summer. 6. Population size, growth, recruitment, and mortality rates of the shorter-lived E. capsaeformis were correspondingly higher than those of E. brevidens and L. fasciola. 7. The federal recovery plan for E. brevidens and E. capsaeformis identifies quantification of demographic variables as a critical step toward meeting the recovery needs of each species. The data collected in this study begin to meet these needs and can be used to monitor and evaluate population performance of each species. Published in 2011 by John Wiley & Sons, Ltd.