Status of Freshwater Mussels in the Ochlockonee River Basin of Georgia and Florida

Abstract

Recent and comprehensive surveys of Ochlockonee River basin mussel fauna are lacking, particularly in the lower portion of the basin which historically has been undersampled. We present the results of surveys conducted between 2006 and 2017 to assess the status of freshwater mussels in the Ochlockonee River basin, and examine historical survey records to assess changes in mussel distribution and population status in recent decades. We gave particular attention to the current status and distribution of 3 federally endangered mussels, Hamiota subangulata (Shinyrayed Pocketbook), Medionidus simpsonianus (Ochlockonee Moccasinshell), and Pleurobema pyriforme (Oval Pigtoe), and 1 threatened mussel, Elliptoideus sloatianus (Purple Bankclimber). During the 12-year period, 3 agencies made 257 collections throughout the basin, encountering 19 of the basin's 22 native mussel species. Shinyrayed Pocketbook and Oval Pigtoe were not detected and are possibly extirpated from the basin. Alasmidonta wrightiana (Ochlockonee Arcmussel), a basin endemic, was not found during the surveys. It has not been collected in more than 85 years, suggesting that the species is likely extinct. A remnant population of Ochlockonee Moccasinshell, also a basin endemic, was detected in a 23-km reach of the lower Ochlockonee River. Although encountered in most of their respective historical ranges, Cyclonaias infucata (Sculptured Pigtoe) and Purple Bankclimber appear to have declined in some areas of the upper basin. Watershed alterations in the basin that may have adversely impacted the mussel fauna include the conversion of forests to agricultural and urban lands, impoundment of the mainstem by Jackson Bluff Dam, introduction of Corbicula fluminea (Asian Clam), and the effects of droughts and water use by humans. Although we detected a relatively intact fauna in the lower Ochlockonee River, our findings suggest declines in 5 mussel species in the basin since 2000, including the 4 federally listed mussels.