American Eel (Anguilla rostrata) Abundance, Distribution, and Size throughout the Lower Ottawa and St. Lawrence River Systems, Ontario, 2009–2013

In support of Ontario’s Species at Risk American Eel Recovery Strategy, a series of quantitative summer electrofishing surveys was conducted in the lower sections of the Ottawa (five reaches), Mississippi (five reaches), and St. Lawrence river systems (two reaches Ontario) and tributaries. These surveys measured density, occurrence, and changes in status of American eels so that efficacy of management and recovery actions can be assessed. Throughout these river systems, 39 indexing locations, each including seven 200-m sites, were quantitatively electrofished annually from 2009 to 2013. Geometric mean density by reach was low in the Ottawa (0.8–2.0 eels·ha^-1) and Mississippi (0.0–0.2) and significantly higher (6.2–23.0) in the St. Lawrence (P<0.0001). Small eels were often electrofished in flowing water near barriers and large eels in bays with inflows. Immigrating and emigrating eels often congregated. In 2011, a pulse of small wild eels (89.6·ha^-1) was detected below the Moses-Saunders dam, St. Lawrence River but not below Carillon, the first dam on the Ottawa. By 2012, some of these small eels started moving upstream, reaching the Mississippi River. Most eels electrofished were in the lowest reaches, particularly below the Carillon and Moses-Saunders dams, and are now very rare in the upper reaches.