Length-specific growth rates in freshwater mussels (Bivalvia : Unionidae):extreme longevity or generalized growth cessation?

1. North American lacustrine freshwater mussels (Bivalvia: Unionidae) are o ne of the world's most imperilled groups of organisms. Knowledge of their a ge structure and longevity is needed for the understanding and management o f mussels. Current methods for age estimation in freshwater mussels are ins ufficient and may have resulted in an erroneous view of the ages of lacustr ine freshwater mussels. 2. We collected growth data through mark-recapture in Minnesota and Rhode I sland, U.S.A., examining four lentic populations of three of the most commo n species of freshwater mussels, Elliptio complanata, Lampsilis siliquoidea , and Pyganodon grandis. Using an inversion of the von Bertalanffy growth e quation, we estimated age at length from length-specific growth relationshi ps. 3. In some populations, lacustrine mussels may be much older than previousl y predicted. Ages predicted from actual growth rates suggest that individua ls in some populations frequently reach ages in excess of a century, placin g unionid mussels among the Earth's longest-lived animals. Alternatively, i f growth has only recently slowed in these populations, generalized growth cessation may be occurring over a broad distributional range of some common North American lacustrine mussels.