Updated 2020-12-04 13:18:30
Lake Ontario -> 1.0 Nearshore Zone Goal -> Eel
Reporting Interval
2014 - 2019
Area
Meeting Target?
Does Not Meet
Indicator Trend
No trend
Confidence?
High
Increasing levels of recruitment to the upper St. Lawrence River/Lake Ontario as measured at the Moses-Saunders Dam eel ladders. At least one million eels ascending the ladders annually
Eel recruitment to Lake Ontario and the Upper St. Lawrence River is represented by the combined, annual number of young American Eel passing through migration ladders situated on the Moses Saunders Power Dam in Ontario and New York (Cairns in press). Since the period in the 1970s and early 1980s when eel recruitment approached or met the FCO target, migrating eel numbers showed a marked decline through to the mid-1990s.
During the reporting period (2014 – 2019), the annual average number of immature eel ascending these ladders was 18,066, a decline of over twenty thousand eel when compared with the average eel passage over the previous reporting period. High flows in the St. Lawrence River resulted in significant water spill through the Long Sault Dam Spillway in 2017 and 2019. This likely reduced ladder use by eel and is at least partially responsible for the decline in recruitment seen between reporting periods. Eel recruitment over the reporting period is 2-3 orders of magnitude below the FCO indicator for Lake Ontario.
Figure 1: Total number of American Eel passing up the eel ladder(s) at the Moses-Saunders Dam, Cornwall, Ontario from 1974-2019. During 1996, the ladder operated however no counts were made. The solid line represents the FCO recruitment goal of 1,000,000 recruits. The dark grey bars represent eel passing the Saunders eel ladder (1974-2019); light grey bars represent eel passing the Moses eel ladder (2006-2019).
Methodology
The largest barriers to migration of American Eel into the Lake Ontario system are power dams on the St. Lawrence River. To enable upstream migration, two eel ladders are maintained on the Moses Saunders Power Dam by New York and Ontario hydroelectricity producers. Electronic counters enumerate young American Eel ascending these two ladders throughout the migration season. Electronic counts are verified manually at regular intervals throughout the ladder’s operation (Kleinschmidt Associates and Riveredge Environmental 2020; Milieu Inc. 2019). The Saunders eel ladder (Ontario) passage time series begins in 1974, with design modifications to improve ladder effectiveness occurring at several points in time. The Moses eel ladder (New York) passage time series begins after its installation in 2006.
Record high flows in the Upper St Lawrence River in 2017 and 2019 likely reduced the number of eel passing through both ladders at the Moses Saunders Dam. Attractive flow from the passage of additional water at the Long Sault Dam Spillway in these years is thought to reduce ladder use by migrating eel. While eel passage numbers from these years are thought to be less representative of the abundance of migrating eel, they do represent annual recruitment to Lake Ontario and the Upper St Lawrence River.
Other Resources
Cairns, D.K. In press. Landings, abundance indicators, and biological data for a potential range-wide American eel stock assessment. Can. Data Rep. Fish. Aquat. Sci. No. X (forthcoming) p
Kleinschmidt Associates and Riveredge Environmental. 2020. 2019 Monitoring of the Eel Passage Facility at the R. H. Saunders Generating Station. Final Report for Ontario Power Generation. 39 pp
Milieu Inc. 2019. Operation and monitoring of the eel-passage facility at the Robert Moses Power Dam in 2019. Report prepared by Milieu Inc. for the New York Power Authority, White Plains, New York.
Contributing Author(s)
- Jake La Rose - OMNRF
- Scott Schlueter - USFWS
- Tom Pratt - DFO