Date of Graduation
Davis College of Agriculture, Natural Resources and Design
Wildlife and Fisheries Resources
Stuart A Welsh
Hydroelectric dams can impact downstream migrating American Eels ( Anguilla rostrata) through migratory delays and turbine mortality. I used radio telemetry to determine the timing and survival of American Eels migrating downstream past five hydroelectric dams on the Shenandoah River in Virginia and West Virginia and through a portion of the Potomac River in Maryland. The five hydroelectric dams implemented a seasonal nighttime turbine shutdown period to protect downstream migrants. The shutdown period was conducted from September 15 to December 15 annually, from 18:00 to 06:00 hours daily. During the fall months from 2007 to 2009, large American Eels were collected primarily by electrofishing above the Luray, Newport, and Shenandoah dams. A total of 145 American Eels were radio-tagged and released near their capture location. All five hydroelectric dams were outfitted with telemetry monitoring equipment to determine the time of arrival to the dam, the time of passage at the dam, the method of passage at a dam, and immediate mortality of tagged fish. Telemetry equipment at the dams was deployed during the fall of 2007 and monitored continuously through the summer of 2010.;A total of 96 tagged American Eels migrated downstream past at least one dam during the study. Downstream passage events occurred during every month of the year except July, with peak migrations in the fall and spring months. The peak timing for downstream migration was different for each of the three study years. A total of 67% of the downstream migration events occurred during the assumed fall migration period (September 15 to December 15). Most (90%) downstream migration events occurred between sunset and sunrise and 81% occurred during the hours used for turbine shutdowns (18:00--06:00 hours). American Eels usually completed downstream migrations during one study year (August 1 to July 31) and multi-year downstream migratory activity for an individual was rarely observed.;Migration out of the Shenandoah River generally took one month to complete, with a mean migration time of 38 d for American Eels to pass all five dams at a distance of 195 km. The majority (81%) of migratory delay experienced at each dam was less than 24 hours in the Shenandoah River. Mean travel speed was similar between the Shenandoah River (29 kmd-1 +/- 12 SE with five hydroelectric dams) and the Potomac River (26 kmd-1 +/- 6.6 SE with only one low head non-hydroelectric dam), suggesting that hydroelectric dams on the Shenandoah River did not cause a substantial migratory delay.;Environmental variables were associated with downstream migration events of American Eels. River discharge, proportional increases in river discharge, and water temperature were significant factors in describing when downstream migration events occurred during the study. A logistic regression model was able to accurately describe when downstream migration events occurred 85% of the time. Lunar phase, time of year, and dam location were not significant variables in describing when downstream migration events occurred.;A total of 28 American Eels experienced immediate turbine mortality during the study. Turbine mortality occurred at all Shenandoah River dams, with individual dam turbine mortality rates ranging from 16%--41% for American Eels passing through turbines. Project mortality rates ranged from 9% to 38% during regular turbine operation and those rates were reduced to 0--6% during the turbine shutdown periods. During all operation scenarios (turbine shutdowns and regular operation), overall mortality rates at each dam ranged from 3--14%, with a cumulative mortality for American Eels passing all five dams of 37%. The seasonal nighttime turbine shutdown period encompassed 50% of the downstream migration events and reduced, but did not eliminate, mortality to downstream migrating American Eels.;Shenandoah River dams likely have little impact on migration delay for American Eels; however, downstream migrations during turbine operation could reduce the number of American Eels leaving the Shenandoah River by 67%. Turbine shutdowns reduced or eliminated mortality during downstream migration events at the Shenandoah River dams. The current time period for implementation of nighttime turbine shutdowns (September 15-December 15) encompassed two-thirds of downstream migration events, however American Eel passage only occurred on a small portion of days during the shutdown period on any given year. On the Shenandoah River, the nighttime turbine shutdown period could be more protective for downstream migrating American Eels if it were implemented based on environmental variable triggers.
Eyler, Sheila M., "Timing and Survival of American Eels Migrating Past Hydroelectric Dams on the Shenandoah River" (2014). Graduate Theses, Dissertations, and Problem Reports. 5561.