Eels at the Edge: Science, Status, and Conservation Concerns

Determining Exit Locations for Eel Ladders at Hydroelectric Power Dams on the St. Lawrence River

Kevin J. McGrath, Richard Verdon, Denis Desrochers, Carole Fleury, Scott Ault, and John Skalski


Abstract.—Additional upstream eel Anguilla rostrata passage is planned at the Moses- Saunders Power Dam, Massena, New York, and has recently been implemented at the Beauharnois Power Dam, Montreal, Quebec, on the St. Lawrence River. Mark– recapture studies were conducted to determine the distance upstream of the dams that eel ladder exits should be located to minimize turbine entrainment. In 2001, 9,822 finclipped eels were released in equal proportions at 0 m, 90 m, and 1,600 m upstream on the west side of the Beauharnois Power Dam. Return rates to the tailwater were 4.5%, 5.0%, and 3.2%, respectively. In 2002, 16,697 fin-clipped eels were released at the same distances on the east side of the dam. Return rates were 12.0%, 4.2% and 1.1%, respectively. In 2001, 4,400 PIT-tagged eels were released at six locations upstream of the Moses-Saunders Power Dam. Eels released further than 270 m upstream of the dam exhibited a return rate of less than 7%, while those released closer than 270 m had a substantially higher return rate, approximately 50%. Even though the dams are very similar in size and hydraulic capacity, return rates of eels released close to the two dams were substantially different, approximately 50% for the Moses-Saunders Power Dam versus 4.5% (west side) and 12.0% (east side) for the Beauharnois Power Dam. These studies indicate that the siting of an eel ladder exit to minimize entrainment is specific to each dam.