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Potential Recovery of the Mussel Fauna of the Clarion River, Pennsylvania

ABSTRACT The Clarion River, a tributary of the Allegheny River in northwestern Pennsylvania, underwent heavy industrialization during the late 19th and early 20th centuries. In the early 1900s, eight tanneries, 11 wood chemical plants, and a large paper mill operated on the Clarion River, releasing a cumulative 98 million liters of industrial effluent daily, in addition to the discharge of coal-mining wastes. By 1911, aquatic life was considered eliminated from the river, but its original mussel fauna was never recorded. In 1993, four living individuals of Strophitus undulatus, the Creeper, were discovered by chance near Clarington, Forest County, which constituted the first documented collection of mussels from the river. I conducted qualitative shell surveys from 2007 to 2019 at 157 sites to document past and present mussel distribution along a 55-km reach of the river. Recently dead shells, weathered shells, or living individuals of S. undulatus were encountered at 146 sites within the study reach. Relic shells of Actinonaias ligamentina were found at 12 sites, recently dead shells and one living individual of Lampsilis fasciola were found at five sites, and a single recently dead shell of Lampsilis ovata was collected. Ages of a subsample of 60 recently dead S. undulatus ranged from 2 to 16 yr (mean = 8.0 yr) and length ranged from 26.8 to 81.7 mm (mean = 29.8 mm), suggesting that natural recruitment may be occurring in the river. Source populations for recolonization of the river are unknown, but tributaries of the Clarion River are a possibility. My results suggest that the Clarion River now supports a substantial mussel population, but additional surveys are needed to provide a baseline for monitoring future recovery.