The Effects of Perched Culverts on Eel Populations in the Hudson River Watershed

A decline in the American eel (Anguilla rostrata) population has recently been noticed along the eastern coast of North America. Along with pollution and invasive parasitic species, researchers suggest that physical barriers are contributing to this population reduction. In smaller tributaries, dams have been observed to have a negative impact on stream connectivity. However, little work has been conducted to see if culverts have a similar negative impact on limiting the upstream migration of eels. This study focused on the perched culvert which is a culvert located above the water level of a stream. The purpose of this study was to gather data about eel populations in the Hudson River Watershed and to see whether or not they are being affected by the presence of perched culverts. A total of 12 culverts sites were sampled, 5 of which contained eels. At each site, the altitude, distance from river, number of barriers between the culvert and the river, and other site characteristics such as water quality were recorded. Eel populations were enumerated by performing a two-pass sequential removal backpack electroshocking in 3 locations relative the culvert: downstream, upstream, and before the next barrier. For population calculations, upstream and next barrier locations were summed together. The density of eels at each location was calculated using the estimated area measured. The true population size of eels at each location was estimated using a series of two-pass depletion equations. The relative health of eels was determined by comparing length and weight values of sedated eels. Across the 5 successful sites, a total of 32 eels were caught or seen downstream of the perched culverts and 5 were found upstream. No abnormalities in eel length/weight were observed. Total eel population numbers at each of the 12 sites were compared to different site characteristics in order to investigate eel presence. As the distance to the river and the number of barriers between a site and the river increased, fewer eels were found. As the elevation of certain sites increased, fewer eels were found, but a definite trend was not clear. Results suggest that perched culverts act like dams in that they inhibit the upstream migration of eels in smaller tributaries. Site characteristic comparisons suggest that too few eels are reaching distant culverts to determine whether or not the culvert’s presence is affecting those eels. These results may be used in future management decisions regarding the prioritization of new and existing culvert mitigation projects in the Hudson Valley.