Elvers find their way up wet rocks to a water source near the base of Conowingo Dam on the Susquehanna River. Credit: USFWS

The Maryland Fisheries Resource Office (MFRO) captured over 4000 young American eels, called elvers, at the base of Conowingo Dam on the Susquehanna River as part of a study designed to test methods for eel passage.  American eel populations have been declining since the early 1980's throughout most of their range along the Atlantic coast. Although the Chesapeake Bay and tributaries support a large portion of the coastal eel population, the construction of 4 hydroelectric dams (including Conowingo Dam) in the early 1900's blocked eels from entering the Susquehanna River watershed.  A fish lift is in operation at Conowingo Dam for passing American shad and other anadromous fish, but is not effective for passing elvers.

To reestablish eel populations in over 400 miles of the Susquehanna River, upstream and downstream passage needs to be addressed.  American eels have a catadromous life cycle in which the Gulf Stream carries larval eels from their natal Sargasso Sea in the Atlantic Ocean to the coast of North America.  Many eels enter the Chesapeake Bay where they swim upstream into brackish or fresh water.  Streams, rivers, and estuaries are home to eels for 8 to 25 years until they become sexually mature and return to the sea to reproduce.  When passage to rivers and streams is blocked to eel, they can become overabundant at the base of dams and in small tributaries where they fall prey to fish and birds.  The objective of this project is to determine the most effective methods for collecting and passing American eels to the upstream portion of the Susquehanna River.

The MFRO collected baseline information on abundance, timing of migrations, catchability and attraction flows for eels at the base of Conowingo Dam. After monitoring collection devices from May to August, 2007, it was determined that Irish elver ramps placed on the river bank were the most effective method of capturing elvers. Information collected for this study will help determine the best location and type of passage needed at the first hurdle to eel migration on the Susquehanna River.