Simulated effects of hydroelectric project regulation on mortality of American eels

Publication Date



American Fisheries Society Symposium 33

Publication Title

Biology, Management, and Protection of Catadromous Eels

Start Page


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Publication Place

Bethesda, MD


American Fisheries Society


We used six years of silver-phase American eel Anguilla rostrata catch data from a weir on a Maine river to determine if river flow and rainfall were predictive of eel migration timing and simulate operational modifications at a hypothetical hydroelectric project to mitigate eel turbine and spill-induced mortality, using eel run timing characteristics and environmental data. We found a significant positive correlation between daily river flow and daily proportion of the run, and significantly more eels were captured on days when rain events occurred than on days when no rain occurred. There was no correlation between mean flow during the run and: timing of run initiation (first 5% of the run); number of days between 5 and 25% cumulative migration; or total number of eels captured over the entire run. Simulations showed that mortality of the entire run decreased with increasing spill flow, and also decreased significantly when generation was Suspended on days with significant rainfall. Suspending hydro project operations on dates encompassing 25-75% of the cumulative eel catch caused a reduction in eel mortality of two-thirds to one-half relative to normal operation. Run mortality was further halved when limits on hydro project operation were set using a combination of rainfall events and eel run timing factors. As a strategy for consistently reducing run mortality on an annual basis, suspending generation for a seven day period during the most probable time of peak downstream movement was as unreliable as normal project operation, and was less than half as reliable as limiting hydro project operations on dates encompassing 25-75% of the cumulative eel catch (similar to 30 days). Our simulations provide guidance when modification of hydroelectric project operations is being considered as a mitigative tool for downstream passage of eels, and in identifying critical areas for future research.

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