Status of American Eel populations in the Mohawk River Basin

Background: The waters of the Mohawk River basin are inhabited by one of the richest fish communities on the East Coast.  The American Eel, Anguilla rostrata, is a unique member of this community, exhibiting a catadramous (maturing in fresh water and spawning in salt water) life history.  Like many migratory fish, the American Eel has suffered a general decline across the East Coast largely attributed to barriers to migration and habitat degradation and other anthropogenic disturbances to the point that the species has been recommended for listing under the Endangered Species Act twice in the past ten years  A recent study by Machut et al. (2007) and the implementation of a NYSDEC-initiated citizen science juvenile eel monitoring program (Bowser et al., 2012) have greatly improved our understanding of eel distribution and behavior in the Hudson River and tributaries. However, little work has addressed the distribution of American Eel in the Mohawk River watershed or the factors that drive this distribution.  The presence of Eel in this basin has been confirmed only by a handful of New York State Department of Environmental Conservation (NYSDEC) fish surveys (aimed at sampling other species) over the past 30 years. This is the extent of our current understanding, however, and the density and distribution of this species are largely unknown in this watershed. 

Fig 1: Native range of American Eel. Map from USGS Nonindigenous Aquatic Species (NAS) https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=310.

This knowledge gap is due in part to the fact that surveying American Eel populations is challenging and time consuming with traditional fish sampling techniques (electrofishing, netting, etc.) because the species is largely nocturnal and buries itself in coarse substrates. A more effective survey technique is needed to quickly and inexpensively determine the occurrence (presence or absence) and abundance of American Eel populations across broad spatial scales.

Environmental DNA (eDNA) in water samples has been used effectively to determine the occurrence of some aquatic species but has not been extensively applied to American Eel. Findings from a recent study published by the authors of this proposal found that detection of eDNA in water samples from streams was greater than 90% effective at determining the occurrence of Eastern Brook Trout, Salvelinus fontinalis, and the quantity of DNA in water samples was a significant predictor of population density and biomass (Baldigo et al., 2017). This was one of the first studies to successfully correlate eDNA concentrations to the known abundance of a riverine species. Thus, it stands to reason that eDNA could be similarly used to determine the occurrence and abundance of American Eel populations in the Mohawk River and elsewhere. The Northeast Fishery Center (Lamar, PA) of the U.S. Fish and Wildlife Service, in cooperation with the USGS, recently developed an eDNA marker for detecting American Eel in water samples. We plan to test and calibrate this marker on tributaries to the Hudson River across a range of Eel densities and then use it to determine the distribution and relative abundance of American Eel in the Mohawk River and major tributaries.

Fig 2: USGS technician Raymond Nellis displays a large American Eel captured in Western New York

Objective: Develop a relationship between American Eel DNA quantity and population density on Hudson River tributaries and use this relationship to estimate Eel distribution and abundance on the Mohawk River and major tributaries. This information is critical for planning or prioritizing future dam passageways or removals, habitat-restoration projects, and fishing/harvest regulations that may aid the conservation and recovery of this keystone species.

Approach: The United States Geological Survey (USGS) will conduct electrofishing surveys of at least 10 sites on Hudson River tributaries spanning a range of Eel abundances, including sites where Eel are absent. These data will be used to estimate relative abundance and biomass of Eel populations. eDNA samples will be collected from these same locations and the resulting data will be used to develop a predictive relationship between DNA concentration and Eel abundance.

Additional eDNA samples will then be collected in the Mohawk River Basin from approximately 15 tributary and 20 mainstem sites. This information on Eel DNA quantity will be used in the calibrated model to estimate Eel abundance throughout the Mohawk River Basin.

References:

Baldigo, B.P., Sporn, L.A., George, S.D., Ball, J.A., 2017. Efficacy of environmental DNA to detect and quantify brook trout populations in headwater streams of the Adirondack Mountains, New York. Trans. Am. Fish. Soc. 146, 99-111.

Bowser, C., Mount, S., Walker, L., 2012. The Hudson River Eel Project: Citizen Science Juvenile American Eel Surveys: 2008-2012,

Machut, L.S., Limburg, K.E., Schmidt, R.E., Dittman, D., 2007. Anthropogenic impacts on American eel demographics in Hudson River tributaries, New York. Trans. Am. Fish. Soc. 136, 1699-1713.

Project Location by County

Greene County, NY, Albany County, NY, Delaware County, NY, Fulton County, NY, Hamilton County, NY, Herkimer County, NY, Oneida County, NY, Lewis County, NY, Madison County, NY, Montgomery County, NY,  Fulton County, NY, Schenectady County, NY, Saratoga County, NY