Estimation of Restoration and Population Trends of American Eels in the Upper Connecticut River Using a Life Table Model.

Haro, Alex, U.S. Geological Survey Eastern Ecological Science Center, S.O. Conte Anadromous Fish Research Laboratory, Turners Falls, MA USA

Restoration of American eels (Anguilla rostrata) to upstream habitats blocked by barriers such as dams has only recently been implemented in the northeastern US. Provision of upstream passage at Holyoke Dam on the Connecticut River and annual counts of juvenile eels passed afford an opportunity to approximate the eel population size upstream of the dam from the known age structure of juveniles and a range of literature-based estimates of instantaneous annual mortality. Measured age structure of silver-phase eels passing downstream of Holyoke Dam also allows estimation of age-specific proportion of the population metamorphosing to the silver phase and emigrating to the sea. A life table method was used to estimate these population structure metrics; population estimates showed a dramatic increase from 40,000 to 50,000 fish in 2012 to 100,000 to 150,000 in 2016 and remaining at those levels to 2022. Estimated current (2022) annual numbers of silver-phase eels emigrating downstream past Holyoke Dam range between 16,000 and 17,000 fish. Current level trends in numbers of juvenile eels passed upstream at Holyoke indicate that populations may remain at these levels for the foreseeable future.