Evidence for Decline in the Unionidae of the East Branch Rocky River, Ohio

A survey of freshwater mussels (Mollusca: Bivalvia: Unionidae) was conducted for the East Branch Rocky River, Ohio, during the summer of 2006. Development in this watershed is moderate though rapidly expanding, particularly in the upstream reaches. Perhaps as a consequence, a preliminary search failed to reveal any live mussels in the river in 2003 . The present report is of an extensive survey covering 21 two-hour timed searches for live mussels and shells combined with visual assessments of disturbance and tests for water quality at each site. All searches were visual or by feeling for mussels embedded in the stream bottom where visibili ty was poor. These surveys produced only 34 live animals and 287 empty shells, which included live specimens of Lampsilis radiata /uteo/a, Lasmigona costata, Lasmigona compressa, and Strophitus undulatus as well as fresh shells of Pyganodon grandis. The few sites that contained live animals and fresh shells were isolated, while worn shells were distributed more evenly throughout the river, suggesting a wider distribution of mussels in the past. Present water quality appeared good, and, therefore, the relatively low density and spatial isolation of unionids may reflect local geomorphologic factors combined with historic and current land usage