Freshwater mussel life history and adaptive management at the Claytor Hydroelectric Project, New River, Virginia

摘要

Stantec Consulting was contracted to conduct water quality and mussel surveys on the New River as part of Claytor Dam’s FERC licensing renewal. This study is part of a Freshwater Mussel Adaptive Management Plan (the Plan) that is designed to determine if flow, temperature, and/or occasionally depressed dissolved oxygen (DO) concentrations are affecting freshwater mussels downstream of Claytor Dam over the term of the new license (FERC No. 739). This work was part of a ten year program designed to gain insight into mussel resources in the project area. Water quality measurements were taken using deployed DO and temperature loggers at several sites on the river. Loggers were deployed at site US-2, US-1, DS-1 and DS-3. These were installed in the field earlier in the year and recovered by Stantec in December of 2015. Seasonal temperature patterns did not vary substantially between the four sites. DO was also consistent at three of the sites while DS-1 exhibited DO readings below 4.0 mg/L during the summer months. This indicated that the differences in dissolved oxygen readings were not temperature driven. Mussel surveys were conducted at seven sites on the New River in Virginia with sites in Pulaski, Giles, Montgomery, Radford, Wythe and Carroll counties. Surveys began on October 12th, 2015 and continued until October 20th. Each site was surveyed with a combination of transect and quadrat sampling either by scuba diving or snorkeling. After transects were surveyed, the areas with the highest abundance of mussels was determined and selected for quantitative sampling with 0.25 m~2 quadrats. 100 quadrats were excavated at each site (25 per 10 m segment) with the exception of DS-4 where only 50 quadrats were excavated due to the lack of suitable habitat. A total of 130 mussels were observed alive in the New River during this survey collectively. Cyclonaias tuberculata was the most abundant species with 96 individuals present and Tritogonia verrucosa was the second most abundant species with 26 mussels collected. Recruitment was observed for these two species as multiple year classes were measured. Upstream sites 1B and 2 were observed to have the highest abundance with 52 and 43 mussels collected respectively. Overall mussel densities were low throughout the project area but were especially low below Claytor Dam and the cause is not yet understood. Monitoring in this and subsequent years is expected to shed light on potential causes of impairment.