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COSEWIC assessment and status report on the American Eel in Canada

FEA2 - Eastern St. Lawrence(eastern Quebec)

In FEA2 (Figure 13), indices of juvenile abundance and spawning escapement are available for two small unexploited watersheds (200 km²): Petite Trinité and Sud-Ouest rivers (Verreault 2002; Verreault et al. 2004; Fournier and Caron 2005). Juvenile abundance data are also available from the Bec-Scie River on Anticosti Island.

Figure 13.  Data sites within the ecological freshwater area FEA2, Eastern St. Lawrence.

Figure 13.  Data sites within the ecological freshwater area FEA2, Eastern St. Lawrence.

 

Indices of Juvenile Abundance

Sampling sites on the Petite Trinité River and on the Sud-Ouest River are both about 4 km from the river mouth. On the Petite Trinité River, on the north shore of the Gulf of St. Lawrence, elver counts at a waterfall were evaluated three times per night every four nights between mid-June and mid-August from 1982 to 1985 and from 1993 to 1996 (Raymond and Caron 1997). From 1999 to 2001, eel ascents have been estimated at the same site with a capture-recapture method using the Petersen estimator (Figure 14). Annual abundance of elvers (total length less than 120 mm) has been estimated at 14,000, 20,000, and 18,000, respectively (Fournier and Caron 2005). The second of these methods is much more efficient than the first, so the data collected by the two methods cannot be compared. Electrofishing data collected on the Petite Trinité River in 2001 reported a mean density of 4.05 eels per 100 m² in the principal course of the river compared to 1.09 eels per 100 m² in the upper part and in the tributaries. In lake habitat, estimates varied from 0 to 77.1 eels per ha for a mean density varying from 31.7 to 33.0 eels per ha, depending on the estimator used. Eels were aged from 2 to 28 years with a mean of 10.8 years, a mean length of 421 mm and a mean weight of 173 g (Fournier and Caron 2005).

 

Figure 14.  Indices of juvenile abundance for FEA2: (A) Number of eels caught in the Petite Trinité River (1982-2001, from Fournier and Caron 2005); (B) Year class strength index (YCSI) based on juvenile captures during upstream migration in the Sud-Ouest River (1995-2002, from G. Verreault, MNRF, Secteur Faune Québec); (C) Eels per 100 m² from electrofishing surveys conducted in the Bec-Scie River, Anticosti Island (1988-1996).

Figure 14.  Indices of juvenile abundance for FEA2: (A) Number of eels caught in the Petite Trinité River (1982-2001, from Fournier and Caron 2005); (B) Year class strength index (YCSI) based on juvenile captures during upstream migration in the Sud-Ouest River (1995-2002, from G. Verreault, MNRF, Secteur Faune Québec); (C) Eels per 100 m² from electrofishing surveys conducted in the Bec-Scie River, Anticosti Island (1988-1996).

On the Sud-Ouest River on the south shore of the St. Lawrence estuary, a year-class strength index (YCSI) has been derived from juvenile upstream migration captures from 1999 to 2005 (Figure 14; Verreault, unpublished data). These preliminary data demonstrate a decline of YCSI through time (from 1.55 in 1995 to 0.66 in 2002).

Electrofishing data are also available for the Bec-Scie River, located in southwest Anticosti Island. The drainage area watershed is 131 km2. Surveys were directed on Atlantic salmon (Salmo salar) from 1988 to 1993 but were continued specifically for eels between 1994 and 1996. Electrofishing was conducted using three sweeps in 16 sites, each 100 m2(Raymond and Caron 1997). Mean density within 100 m2 of river was estimated at 17.7 ± 7.1 eels (Figure 14). The lowest density was in 1992 (8.4 eels/100 m2) while the highest occurred the year after with 26.8 eels/100 m2. No trend is apparent in the main course of the river, but densities in one of its tributaries (Ruisseau Castor) showed a downward trend since 1988 (1988: 10.7 eels/100 m2; 1996: 1.1 eels/100 m2).

Recent studies of the American eel in the St. Jean River and Estuary in the eastern Gaspé Peninsula, Quebec (Thibault et al. 2005, F. Caron unpubl.) have shown eels present in substantial numbers, and with a range of ages.  This suggests that recruitment to the area is continuing, although no time series of abundance is available.

Since there is no fishing in the Petite Trinité and Sud-Ouest rivers, estimates of outmigrating silver eels correspond to spawning escapement. On the north shore of the St. Lawrence, maximum spawning escapement in the Petite Trinité River, with a freshwater habitat area of 14.3 km², was estimated at 103.4 kg/year/km². In the Sud-Ouest River, with a freshwater habitat area of 8.7 km², maximum spawning escapement was estimated at 86.8 kg/year/km².