Distribution of American eels (Anguilla rostrata) and the influence of barriers in the Lake Champlain basin

Freshwater eels ( Anguilla spp.) are experiencing significant population declines, particularly for species from temperate latitudes. These declines are attributed to overharvest, habitat degradation, and migration barriers such as dams. However, lack of information about eel distribution, habitat use, and ability to navigate in-stream barriers increases the challenge of managing eels. We investigated the distribution and abundance of eels in the Lake Champlain basin, where 2.7 million glass eels were stocked from 2005 to 2010, and focused on the influence of barriers pre- and post-stocking. Data were collated from a range of sources, from 1929 to 2024. Eels were recorded throughout Lake Champlain and its tributaries, including down to 90-m depth in the lake and distances up to 40 km upstream from the lake. Eels were rarely observed upstream of dams >10 m, and observations were reduced upstream of multiple dams, regardless of dam height. Stocked eels may be expanding the overall distribution of eels in the basin, with post-stocking observations from locations typically considered ‘impassable’. Inconsistency in data collection over space and time has left gaps in our understanding of eel distributions and creates uncertainty regarding accuracy of observed eel absences, issues which could be improved by future survey work. Our findings from the Lake Champlain basin can likely be extrapolated to the larger St Lawrence River basin, where stocking has also occurred, to identify research and management needs regarding the impacts of small dams in minor tributaries and large dams in major rivers.