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Investigation of American Eel Passage at Great Falls on the Potomac River--Study Update, May 2003
Northeast Region, July 9, 2003
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In the first attempt to determine the relative abundance of the migratory American eel on part of the Potomac River, state and federal agencies have begun investigating eel migrations at three locations downstream of the Great Falls dam. [See the original report, "Investigation Looks at American Eel Numbers in Potomac River," dated April 16, 2003.] The investigation involves sampling the potential migration routes at the base of the dam and the National Park Service's C&O Canal. Additional sampling downstream was planned, but due to logistical problems, the sampling was cancelled.

Cooperating agencies working with the Northeast Region's Chesapeake Bay Field Office include the Maryland Department of Natural Resources; Washington, D.C., Fisheries; Interstate Commission on the Potomac River Basin; National Park Service; U.S. Fish and Wildlife Service; U.S. Environmental Protection Agency; and the U.S. Army Corps of Engineers.

The investigation depended on the ability of researchers to collect eels and determine their distribution in four months of sampling from March through June 2003. The objective was to tag one hundred American eels captured at three sites in eel pots fished with equal amounts of effort.

During the first month of the study, five eel pots were used at each of the downstream corners of the dam on the Maryland and Virginia shores and in the C&O Canal at Lock 18. Two days of electrofishing downstream of the three sites were unavoidably lost on account of high water. The river flow swelled to 75 thousand cubic feet per second (cfs) above the median flow of 25 cfs, causing the cancellation of seven sampling days and limiting the eel catch.

Despite the dificult sampling conditions, all the agencies captured and tagged eels. In preliminary results, 122 eels were captured, with 15 to 30 percent recaptured by the last day. The study results will be analyzed and summarized by field office and Maryland Department of Natural Resources staff and reviewed by the cooperating agencies. The data from the three sites will be used to assess the potential of the three locations as passage routes. The information should help American eel restoration in the Potomac River.

Continued sampling at Great Falls in 2004 is under consideration.

Contact Info: Jennifer Lapis, (413) 253-8303, jennifer_lapis@fws.gov



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