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Draft – American Eel (Anguilla rostrata) in Ontario Ontario Recovery Strategy Series

Author:  MacGregor, R., J. Casselman, L. Greig, W. A. Allen, L. McDermott, and T. Haxton.   2010. DRAFT Recovery Strategy for the American Eel (Anguilla rostrata) in Ontario.  Ontario Recovery Strategy Series. Prepared for Ontario Ministry of Natural Resources, Peterborough, Ontario. vii+ 78 pp.

Pages 23 to 24:

Barriers to Migration

Dams can severely impede upstream dispersal of juvenile eels in freshwater if no passage way is provided (Haro et al. 2000). It has been estimated that 85 percent of freshwater habitat for migratory fish in the United States has been lost due to barriers (Lary et al. 1998). In a 1998 study, the U.S. Fish and Wildlife Service determined that eels may have been eliminated from 81 percent of their historic habitat between Connecticut and Maine due to the construction of a large number of dams (ASMFC 2000). Barriers reduced eel densities by at least a factor of 10 on the Hudson River, and eel condition was significantly poorer above barriers (Machut et al. 2007). The situation appears similar in Ontario where at least 953 dams exist within the eel’s historic range (Figure 7). Hydroelectric dams generally pose the most significant barrier to upstream migration due their height. However, with the exception of one eel ladder at the Moses-Saunders facility on the St. Lawrence River, as of 2008 no provisions for upstream fish passage for any species have been made at any of the approximately 200 hydroelectric stations in Ontario.  Negotiations with a few facilities are now underway to correct this situation for upstream eel passage.

Turbines at Hydroelectric Facilities

Hydroelectric facilities in Ontario pose significant challenges to eels (Larinier and Dartiguelongue 1989; Mitchell and Boubée 1992; Desroches 1995; Normandeau Associates Inc. and Skalski 1998; Haro et al. 2000; Dönni et al. 2001, in ICES 2003; McCleave 2001; Allen 2008 b, c, d), as they impart serious individual and cumulative mortalities at the watershed level to downstream migrants en route to spawn (McCleave 2001; MacGregor et al. 2009). There are 87 hydroelectric facilities within the historic range of eels in Ontario, and 30 within the post-2000 range (Figure 8). As of 2009, many of these facilities continue to cause annual eel mortalities (Community Stewardship Council of Lanark County 2010; A. Bendig, pers. comm. 2009; K. Punt, pers. comm. 2009). With the exception of recent trap and transport efforts at Moses-Saunders, mortalities due to turbines at all hydroelectric facilities in Ontario continue unmitigated on most watersheds.

When eels were abundant in North American watersheds, entanglement in turbines was sufficient to cause major operational difficulties or complete shutdowns of power plants and mills, and these mortalities have been ongoing for decades at many facilities (MacGregor et al. 2009). The following quote from a 1902 newspaper article regarding a large sawmill at Chaudier Falls (a site where hydroelectric facilities now are installed to serve the City of Ottawa) paints a vivid picture of the large number of eels once passing downstream in the Ottawa River at that time:

“Hull, Canada: A turbine mill wheel which runs a gang of saws at the Chaudier waterfall stopped suddenly. Upon shutting down the mill and unscrewing the upper cap, it was discovered that the wheel had become packed full of eels. It looked as though there must have been hundreds of thousands of them.” (Reading Eagle 1902; St. John Daily Sun 1902).

Cumulative mortalities of eels passing through a series of hydroelectric facilities on smaller watersheds can also be very high, at times approaching 100 percent. For instance, Dönni et al. (2001, in ICES 2003) estimated an average annual mortality of 92.7 percent for European Eel (A. anguilla) in the River Rhine for a succession of 12 hydroelectric facilities in Germany. This suggests that cumulative turbine mortalities imposed by a series of facilities on the Trent and Ottawa Rivers (MacGregor et al. 2009) could also be very high. While American Eel have declined substantially in abundance in inland watersheds of Ontario, electrofishing and tailrace surveys in 2009 and photographs submitted to the Ontario Ministry of Natural Resources in 2007/2008 have demonstrated that eels are still being killed by hydroelectric facilities in the Ottawa, lower Trent, and Mississippi Rivers (A. Bendig, pers. com. 2009; Community Stewardship Council of Lanark County 2010, MacGregor et al. in prep.). On the St. Lawrence River, cumulative turbine mortality of eels at the Beauharnois and Moses-Saunders facilities during their downstream spawning migration has been estimated to be 41 percent (Desroches 1995; Normandeau Associates Inc. and Skalski1998).

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