Effects of the development of a newly created spawning ground in the Des Prairies River (Quebec, Canada) on the reproductive success of lake sturgeon (Acipenser fulvescens)

In the fall of 1996, the surface area of an existing spawning ground located downstream of a power dam on the Des Prairies River was expanded. More than 8000 m 2 of appropriate substrate were then added to the largest lake sturgeon spawning ground in the lower St. Lawrence River system. The impact of this enhancement project was monitored 3 years before (1994-1996) and 7 years after (1997-2003) habitat modification. Four hypothesis were tested: (i) the newly created spawning ground was utilized by lake sturgeon for egg laying, (ii) the utilization of the newly spawning bed improved the reproductive success of lake sturgeon, (iii) the improvement of the reproductive success increased the lake sturgeon larvae production, and (iv) the increase of larvae production increased the recruitment of lake sturgeon. After the new spawning area was developed, the sampling station located in this new section was one of those most used for egg deposition, under both high (1997) and low (1998-1999) flows conditions. Absolute annual numbers of drifting larvae varied between 1.2 million (1996) and 12.8 million (2003). The mean survival rate of the estimated number of laid eggs compared with drifting larvae was 0.88 and 0.93% in 1995 and 1996, respectively, relative to 5.6% in 1997, 3.82% in 1998 and 2.41% in 1999. These results indicate that the new area had a positive impact on the reproductive success of lake sturgeon in the Des Prairies River. From 1994 to 2003, strong cohorts in the lower St. Lawrence system were related to high larval drift in this river. However, high larval production did not necessarily lead to a strong cohort, and year-class strength determination also appeared affected by environmental factors, with the strongest year classes all associated with high June flow rates (over 1150 m 3 s(-1)) in the Des Prairies River. The information gathered during this study enabled us to refine previous observations on the management of sturgeon spawning grounds and the planning of their design, surface area, substrate and location, as well as other physical parameters.