Observations of American eels using an upland passage facility and effects of passage on the population structure

Over two seasons, we observed passage of American eels Anguilla rostrata at an eel passage facility (eel ladder) placed adjacent to an upland mill dam on a small tributary to the Hudson River, New York. American eel use of the ladder was significantly correlated with freshets and moon phase, similar to other studies of eel migration. Most of the migrants were young (<20 cm total length). Several large American eels (>35 cm) exhibited local movements, including use of the ladder, as shown by recaptures of individuals marked with coded wire tags. Operation of the eel ladder greatly reduced the density of small American eels below the mill dam. Placing eel ladders on upland obstructions has the potential to enhance the productivity of silver (sexually mature) eels, an important consideration in the Hudson Valley, where hundreds of barriers have been constructed on upland tributaries.