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Over the last six decades, global hydropower capacity has more than doubled; yet, at the same time, migratory fish populations have declined more than 75%. This fact underscores a pressing challenge: the growing demand for clean energy must align with the need to conserve ecosystems. The interplay of hydropower sites and American eels exemplifies this issue. Here’s why eel passage warrants our attention.
EELS ARE ECOLOGICALLY AND CULTURALLY SIGNIFICANT
American eels have a unique lifecycle, migrating from ocean to freshwater and back (a reverse migratory process as compared to salmon). This journey makes them especially vulnerable to hydropower turbines when they migrate downstream to spawn as mature adults. Eels play a crucial ecological role, historically comprising up to 50% of the biomass in some rivers, serving as both prey and predator, and acting as primary hosts for Eastern elliptio freshwater mussel larvae, essential for water quality.
Eels also hold cultural significance, particularly for Indigenous communities like the Haudenosaunee, who honor eels for their role in purifying waters and view them as leaders linking the spiritual and natural worlds. As eel populations have declined, Indigenous relationships with eels have strained, resulting in lost traditions and heritage.
Members of the Mohawk Council of Akwesasne and the River Institute work collaboratively to collect, assess and document dead and injured eels below a hydropower site on the St. Lawrence River in Canada. The project aims to collect data that will support eel conservation, while also restoring lost connections between eels and Indigenous people in Akwesasne. Image courtesy of Courtney Holden and Logan Lazore.
HYDROPOWER’S IMPACT ON EEL POPULATIONS
Dams and turbines pose significant threats to eels. Studies have shown substantial declines in eel populations in eastern rivers due to dams. For instance, telemetry studies indicate that while individual survival rates for eels navigating through hydropower sites might in some cases be acceptable, cumulative survival through multiple dams is significantly lower. This aggregate impact necessitates comprehensive mitigation strategies.
Sheila Eyler of USFWS described that because eels spend 15-30 years maturing upstream, the implications of dams on eel populations can take generations to manifest. This chart illustrates how dam construction on the Susquehanna river has contributed to the eel population decline. Image courtesy of Sheila Eyler.
THE STATE OF DOWNSTREAM EEL PASSAGE AT HYDROPOWER SITES
Contemporary technologies for eel protection include physical exclusion screens, bypass systems, trap and haul programs, and fish-friendly turbine designs. However, there is variability in their effectiveness. Balloon tagging and telemetry studies help understand eel movements and survival rates, guiding the development of better protective measures. Innovations like turbines designed for safe downstream fish passage have demonstrated high survival rates for eels and present a potential solution for sites where screening is ineffective or cost-prohibitive.
Stills from a video shown by Steve Amaral of Alden Research Laboratory (now Verdantas) depict an adult eel passing downstream through a screen with 0.75-inch clear bar spacing. This spacing is recommended by USFWS to exclude eels from entering turbines but is not always effective. Images courtesy of Steve Amaral.
Abe Schneider and Sterling Watson of Natel Energy shared information about Natel’s FishSafe RHT designs that have exhibited 98-100% survival for through-turbine eel passage. Image courtesy of Natel Energy.
Currently, efforts are underway within the U.S. Fish and Wildlife Service in collaboration with the National Marine Fisheries Service to update fish passage guidelines and develop new survival standards for eels at hydropower sites. Continued dialogue between these agencies and hydropower operators is crucial to ensure these guidelines reflect the latest scientific knowledge and best available technological advancements.
WHY WE SHOULD ACT NOW TO IMPROVE EEL PASSAGE
In the next decade, a significant portion of the U.S. hydropower fleet will undergo relicensing and/or be in need of modernization. Now is the opportune time to implement eel-friendly technologies — addressing eel passage issues is not only about conservation but also about ensuring hydropower’s sustainability as a baseload, dispatchable, renewable resource.
By integrating advanced technologies and adhering to updated guidelines, the hydropower industry can play a pivotal role in preserving eel populations and the critical ecosystem services they provide, ensuring a balanced and sustainable approach to energy production and biodiversity conservation.
LEARN MORE ABOUT CHALLENGES FACING EELS AND HYDROPOWER AND THE POTENTIAL SOLUTIONS
A workshop exploring this topic at Waterpower Week 2024, Eels – Understanding Their Importance and Enabling Safe Downstream Passage Through Hydropower Sites, featured speakers from Natel Energy, U.S. Fish and Wildlife Service, the Mohawk Council of Akwesasne, the River Institute, Normandeau Associates, Low Impact Hydropower Institute, U.S. Geological Survey, and U.S. Department of Energy.
You can find more information and resources from the workshop here, including:
- A detailed report summarizing the content presented
- Downloadable presentations by speaker
- A video recording of the full four-hour workshop
