American eel Anguilla rostrata abundances have undergone significant declines over the last 50 years, and migration barriers have been recognized as a contributing cause. We evaluated eel abundances in headwater streams of Shenandoah National Park, Virginia, to compare sites before and after the removal of a large downstream dam in 2004 (Embrey Dam, Rappahannock River). Eel abundances in headwater streams increased significantly after the removal of Embrey Dam. Observed eel abundances after dam removal exceeded predictions derived from autoregressive models parameterized with data prior to dam removal. Mann–Kendall analyses also revealed consistent increases in eel abundances from 2004 to 2010 but inconsistent temporal trends before dam removal. Increasing eel numbers could not be attributed to changes in local physical habitat (i.e., mean stream depth or substrate size) or regional population dynamics (i.e., abundances in Maryland streams or Virginia estuaries). Dam removal was associated with decreasing minimum eel lengths in headwater streams, suggesting that the dam previously impeded migration of many small‐bodied individuals (<300 mm TL). We hypothesize that restoring connectivity to headwater streams could increase eel population growth rates by increasing female eel numbers and fecundity. This study demonstrated that dams may influence eel abundances in headwater streams up to 150 river kilometers distant, and that dam removal may provide benefits for eel management and conservation at the landscape scale.

Hydroelectric dams impact the downstream migrations of silver American Eels Anguilla rostrata via migratory delays and turbine mortality. A radiotelemetry study of American Eels was conducted to determine the impacts of five run‐of‐the‐river hydroelectric dams located over a 195‐km stretch of the Shenandoah River, Virginia–West Virginia, during fall 2007–summer 2010. Overall, 96 radio‐tagged individuals (mean TL = 85.4 cm) migrated downstream past at least one dam during the study. Most American Eels passed dams relatively quickly; over half (57.9%) of the dam passage events occurred within 1 h of reaching a dam, and most (81.3%) occurred within 24 h of reaching the dam. Two‐thirds of the dam passage events occurred via spill, and the remaining passage events were through turbines. Migratory delays at dams were shorter and American Eels were more likely to pass via spill over the dam during periods of high river discharge than during low river discharge. The extent of delay in migration did not differ between the passage routes (spill versus turbine). Twenty‐eight American Eels suffered turbine‐related mortality, which occurred at all five dams. Mortality rates for eels passing through turbines ranged from 15.8% to 40.7% at individual dams. Overall project‐specific mortality rates (with all passage routes combined) ranged from 3.0% to 14.3%. To protect downstream‐migrating American Eels, nighttime turbine shutdowns (1800–0600 hours) were implemented during September 15–December 15. Fifty percent of all downstream passage events in the study occurred during the turbine shutdown period. Implementation of the seasonal turbine shutdown period reduced cumulative mortality from 63.3% to 37.3% for American Eels passing all five dams. Modifying the turbine shutdown period to encompass more dates in the spring and linking the shutdowns to environmental conditions could provide greater protection to downstream‐migrating American Eels. Received October 16, 2015; accepted April 3, 2016 Published online August 3, 2016

Worldwide populations of freshwater eels have declined with one of the contributing causes related to mortality during passage through hydropower turbines. An inherent trade-off underlies turbine management where the competing demand for more hydropower comes at the expense of eel survival. A win-win solution exists when an option performs better on all competing demands compared to other options. A predictive model for eel migration based on a recent telemetry study was used to develop decision rules for turbine management in the Shenandoah River system. The performance of alternative decision rules was compared to the status quo policy to search for win-win solutions. Decision rules were defined by the probability of eel movement and were evaluated by the probabilities of false positive and false negative errors.The exact value of the cut-off probability used in the decision rule will need to be determined through negotiation between stakeholders, but a range of cut-off probabilities resulted in a win-win situation with both reduced eel mortality and increased turbine operation relative to the current shutdown strategy. Monitoring the implementation is needed to evaluate and update the predictive model and to refine the decision rule. Although the decision is framed for the Shenandoah River system, the analytical approach could be used to develop decision rules for turbine shutdown policy in other areas.

Dams and their associated effects on the migration and mortality of the American Eel Anguilla rostrata have been implicated as a significant factor in the current depleted status of the species along the Atlantic coast of North America. Female American Eels that mature in areas below dams may be smaller and have lower fecundity than individuals that mature in more upstream reaches of a river system. However, increased mortality associated with downstream migration through hydroelectric turbines may negate any reproductive advantage afforded to American Eels occupying areas upstream of hydroelectric facilities. We developed an American Eel egg‐per‐recruit (EPR) model to investigate how various levels of upstream and downstream passage may affect the reproductive output from rivers with hydroelectric facilities. We applied our model to the Susquehanna River and found that if American Eels are passed upstream of multiple dams on the river, cumulative downstream passage survival must be ≥33% for the upstream passage to be beneficial; otherwise, upstream passage is likely to result in an EPR deficit when compared with no passage. Cumulative downstream passage survival would need to increase substantially above 33% to have a high probability of making any gains in terms of EPR. Our EPR modeling framework can be adapted to other systems and used to make recommendations for necessary upstream and downstream passage for the conservation of American Eels in rivers impacted by hydroelectric facilities. Received December 24, 2013; accepted March 28, 2014

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 Many people have assisted me in pursuing my degree, and without their help, compl...