1. North American lacustrine freshwater mussels (Bivalvia: Unionidae) are one of the world’s most imperilled groups of organisms. Knowledge of their age structure and longevity is needed for the understanding and management of mussels. Current methods for age estimation in freshwater mussels are insufficient and may have resulted in an erroneous view of the ages of lacustrine freshwater mussels. 2. We collected growth data through mark‐recapture in Minnesota and Rhode Island, U.S.A., examining four lentic populations of three of the most common species of freshwater mussels, Elliptio complanata, Lampsilis siliquoidea, and Pyganodon grandis. Using an inversion of the von Bertalanffy growth equation, we estimated age at length from length‐specific growth relationships. 3. In some populations, lacustrine mussels may be much older than previously predicted. Ages predicted from actual growth rates suggest that individuals in some populations frequently reach ages in excess of a century, placing unionid mussels among the Earth’s longest‐lived animals. Alternatively, if 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.

Freshwater mussels (Bivalvia: Unionidae) have been an economically valuable biological resource in North America since the mid-1800s. Although the industries based upon mussel harvest are quite distinct from one another, the trends apparent in harvest statistics are remarkably similar among each successive harvest era. Whether fished for freshwater pearls, button production, or cultured pearl production, market factors have driven commercial harvests while the life history and ecology of mussels have been largely ignored. Annual yields of freshwater mussels are declining throughout the United States and catch per unit effort (CPUE) has declined dramatically in some of the most important American mussel fisheries. Harvest statistics indicate that mussel populations are dangerously depleted due to the erosion of the latest industry based upon their harvest. It seems likely that the exhaustive harvests of both the distant and recent past, coupled with habitat loss and degradation, have left North American unionid mussel populations at levels insufficient to support the substantial harvests consistently demanded by industry. This century-long exploitation trajectory provides valuable lessons about the mechanisms of fisheries collapse that are necessary to ensure the sustainable management of aquatic resources.

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