Spawning, early life history, and physical characteristics of lake sturgeon (Acipenser fulvescens) spawning grounds were compared between two rivers located in the Montréal region. The spawning grounds in Des Prairies River were enlarged in 1985, during the reconstruction of the Des Prairies power plant spillway. The L'Assomption River spawning ground has not been physically altered by human activities. In 1989, spawning occurred between May 14 and 27 in Des Prairies River (water temperature 11.6–15.4 °C) and between May 15 and 22 in L'Assomption River (water temperature 11–21.5 °C). On a given date, embryos were slightly more developed in L'Assomption River, where hatching began 3 days earlier than in Des Prairies River (26 vs. 29 May). The great similarity in the spawning and early development sequence suggests that spawners utilizing these two rivers cannot be differentiated on the basis of these biological characters. In 1990, larval emigration from the Des Prairies River spawning ground began on May 29, 11 days after peak spawning. The larvae drifted to the St. Lawrence River in June (peak on 16 June), at a mean length of approximately 20 mm. In both rivers the proportion of stations with eggs present tends to decrease as depth and current velocity increase. Egg deposition occurs on a wide variety of substrate types, ranging from fine- to medium-sized gravel to boulders. Although utilization varies with prevailing hydrological conditions, in 1990 the artificial spawning bed in Des Prairies River showed a high proportion of stations with eggs present.

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)(1995)(1996) and 7 years after (1997)(1998)(1999)(2000)(2001)(2002)(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.

Despite frequent use of length-based condition indices by fisheries managers and scientists to describe the overall well-being of fish, these indices are rarely evaluated to determine how well they correlate with more direct measures of physiological or ecological condition. We evaluated common condition indices (Fulton's condition factor K F , Le Cren's condition index K LC , and two methods of estimating relative weight W r ) against more direct measures of physiological condition (energy density, percent lipid content, and percent dry mass) and ecological condition (prey availability) for lake whitefish Coregonus clupeaformis in Lake Huron. We developed four standard weight (W s ) equations using the regression length percentile (RLP) method: one for the species as a whole, and three separate equations describing immature, mature male, and mature female lake whitefish from 385 populations in North America. Species RLP-W s showed less lengthrelated bias and more closely matched empirical quartiles of lake-specific mean weight than did maturity-or sex-specific RLP-W s equations. Significant length-related bias was detected in EmP-W r . No biologically significant length-related bias was detected in K LC , but this index was specific to a single population of fish. Species RLP-W r showed no significant length-related bias, and K F was significantly size dependent. All length-based condition indices were significantly correlated with energy density, percent lipid content, and percent dry mass. The index most strongly correlated with all three measures of physiological condition was K F , likely because both the physiological measures and K F exhibited positive relationships with body size. Across two Lake Huron sites, RLP-W r was significantly correlated with density of prey (amphipods Diporeia spp.). Of the two condition indices developed in this study, RLP-W r was consistently more strongly correlated with physiological condition indices than was EmP-W r .

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