Passage Technologies for American Eels

Science Center Objects

The American eel (Anguilla rostrata) migrates into freshwater in the juvenile (glass eel and elver) stage, feeds and grows in freshwater habitats, and migrates downstream to the ocean to spawn as an adult. Migrating eels frequently encounter barriers in river environments, primarily in the form of dams, that limit access of juveniles to upstream growth habitat, and can injure or kill adult downstream migrant eels that pass through turbines or over spillways.  Recent concerns of a decline in recruitment of American eels has prompted efforts to restore this species to historic habitats by providing safe, timely, and effective passage for both juveniles and adults at riverine barriers, including hydroelectric dams.  

Traditional fishways and fish lifts are generally inefficient in passing eels. Specialized upstream eel passage structures (e.g., climbing ramps) can be more effective, but many aspects of their performance are poorly understood, and they require additional refinement and standardization. Technologies for preventing mortality and injury of downstream migrant eels passing through turbines at hydropower projects are also not well developed.

This research seeks to design, evaluate, and improve technologies for passing eels upstream at dams and other structures, and to provide safe and effective passage of downstream migrant eels at hydropower dams and other barriers.

Specific objectives include:

  1. Laboratory evaluation of performance of upstream eel passage structures, primarily in the form of eel climbing ramp and trap devices, but also with limited testing of traditional small-scale fishways (e.g., Denil, Alaska steeppass, pool-and-weir types) which currently have unknown performance for passing juvenile eels.
  2. Laboratory evaluation of downstream passage mitigation structures, including reduced intake bar rack spacing or overlays, varying approach velocity, behavioral barriers (light, electricity) and bypass systems.
  3. Field evaluation of downstream passage of eels at several sequential dams within a single watershed.

Application of the results will ultimately have relevance to quantification and reduction of potential impacts of dams and other barriers on migrating juvenile and adult eels. Information on operation and design gained from these studies can be directly applied to formulating guidelines and improvements of passage structures and their operation that will benefit regulating agencies (USFWS, NMFS, States), the private sector, and various NGOs.

Adult silver phase American Eel

A silver-phase American Eel in a northeastern river begins migrating downstream to the ocean to spawn in the Sargasso Sea. The migration can span hundreds of kilometers in freshwater rivers and thousands of kilometers at sea.

(Credit: Alexander Haro, USGS Leetown Science Center. Public domain.)

Eel climbing substrate

Left: Prototype ABS plastic eel climbing ramp under development and testing at CAFRL. New substrate design allows for passage of a wider size range of eels with less need for precise flow regulation. Right: juvenile eel climbing wetted ABS plastic substrate.

(Credit: Alexander Haro, USGS Leetown Science Center. Public domain.)

Release of radio-tagged silver phase American Eel

Radio-tagged silver phase American Eels being released for a CAFRL telemetry study of downstream passage of eels at hydroelectric dams on the Shetucket River, Connecticut.

(Credit: Alexander Haro, USGS Leetown Science Center. Public domain.)

Eel airlift bypass prototype

Prototype design of an airlift developed at CAFL to transport downstream migrant eels through a bypass pipe and away from turbine intakes. The airlift design passes eels as well as a conventional siphon or gravity pipe.

(Credit: Alexander Haro, USGS Leetown Science Center. Public domain.)

Eel electrosensitivity test apparatus

Apparatus used to test the sensitivity of eels to low-voltage pulsed DC electric fields. Knowledge of sensitivity of eels to electric fields enables development of behavioral barriers that use electricity to guide eels away from turbine intakes.

(Credit: Alexander Haro, USGS Leetown Science Center. Public domain.)