The objectives of this study were to (i) assess the variation in relative abundance of lake sturgeon (Acipenser fulvescens Rafinesque, 1817) subjected to various man-induced stresses and physical characteristics at a landscape scale across Ontario; and (ii) ascertain the factors that explain the variability observed among rivers using a multivariate approach. A standardized index netting program targeting juvenile and adult Lake Sturgeon was conducted over two field seasons at 22 river sites across Ontario. Each river had unique or different human-induced stresses and physical characteristics. Relative abundance of Lake Sturgeon varied in river across the Ontario landscape. A principal component analysis was conducted using site physical characteristics with the associated anthropogenic stressors. The catch-per-unit-effort (CPUE) for juvenile and adult Lake Sturgeon were then regressed with the scores of principal components having eigenvalues >1. The variation observed was best explained by the negative relationship observed between CPUE and the presence of hydroelectric generating stations. Historical commercial fisheries also had an effect on Lake Sturgeon abundance whereas subsistence fisheries seemed to focus on rivers that were not regulated and where Lake Sturgeon numbers were greater. Research and recovery efforts should focus on minimizing the impact of hydroelectric generation on Lake Sturgeon while achieving socioeconomic goals. U.S.

The presence of hydroelectric power generating facilities has been identified as the primary factor affecting the variation in relative abundance of Lake Sturgeon Acipenser fulvescens in rivers across Ontario. Qualitatively, these facilities are known to have impacts on the aquatic environment, and they can be inferred to have effects on Lake Sturgeon; however, few studies quantifying these effects are available. Our objectives were to (1) determine and compare the magnitude of effect (d) of hydroelectric facility operating regimes on Lake Sturgeon abundance;(2) compare Lake Sturgeon biological responses among river systems with different operating regimes in order to understand the potential limiting factors within these systems; and (3) assess the effectiveness of mitigation efforts where they have been employed. A standardized index netting program targeting juveniles and adults was conducted over two field seasons at 23 river sites across Ontario. The magnitude of effect on abundance (as indicated by d) was lowest in run-of-the-river systems and was considered large in peaking systems and winter reservoir systems. Relative abundance was significantly greater in unregulated rivers than in regulated rivers. Juvenile abundance was significantly greater in run-of-the-river systems than in peaking systems and winter reservoirs and was significantly greater in peaking systems than in winter reservoirs. Adult abundance did not significantly differ among operating regimes. Growth was faster and condition was significantly greater in unregulated systems than in regulated systems. Recruitment of Lake Sturgeon was highly variable in both regulated and unregulated systems, whereas recruitment failure was more evident in regulated systems, particularly in peaking systems.

Large-bodied fish assemblages were assessed in large rivers across Ontario. The objectives of this study were to (i) determine if there were relationships in large-bodied fish species within rivers;(ii) determine what factors explain the variability in the abundance of large-bodied fish within rivers across Ontario; and (iii) assessed variation in large-bodied fish biodiversity among these river.Standardized index netting was conducted at 22 sites across 12 major rivers and sampled 3889 fish representing 26 species. Species associations were evident based on correspondence analysis. Walleye, Common White Sucker, Northern Pike and Lake Whitefish formed one group; Silver Redhorse, Shorthead Redhorse and Lake Sturgeon (adult and juvenile) formed another; Burbot, Longnose Sucker and Sauger were closely associated; and Cisco, Yellow Perch, Rock Bass, Smallmouth Bass and Brown Bullhead grouped. Canonical correspondence analysis was conducted to link species abundance patterns to environmental conditions. Walleye, Common White Sucker, Lake Whitefish and Smallmouth Bass were ubiquitous. Northern Pike abundance was negatively correlated with river discharge and longitude. Burbot, Sauger and Longnose Sucker abundance were positively correlated with deep rivers and discharge. Whereas Cisco, Yellow Perch and Rock Bass abundance were greater in wider rivers with lower discharge. Lake Sturgeon (adult and juvenile), Silver Redhorse and Shorthead Redhorse abundance were greater in narrow, longer rivers. Juvenile Lake Sturgeon abundance was positively correlated with longitude and river discharge. Mean species diversity and richness of large-bodied fish among all sites was 1.58 (0.36 SD) and 7.7 (2.6 SD). Species diversity was not significantly related to any of the variables used in the Generalized Linear Model; however, species richness was significantly related to maximum depth. This study demonstrated subtle differences in environmental variables affecting large-bodied fish at the landscape scale rather than those observed at the river scale.

Summary Lake Sturgeon, Acipenser fulvescens, was assessed in a large, pristine river in northern Canada using a standardized protocol. Gill netting (38‐127 mm and 204‐306 mm stretched mesh) was conducted at five sites averaging 37 rkm in the Attawapiskat River in Ontario. The objectives were to ascertain relative abundance of Lake Sturgeon within a northern river; determine if Lake Sturgeon are randomly distributed within a ‘pristine’ river; assess if there is evidence of spatial structuring; and determine if there is genetic structuring within the river. Over the two years (2015 and 2016), 176 Lake Sturgeon were sampled with a mean total length of 851.1 mm (323.4 SD) and mean age of 21 years (12.2 SD). There was a significant difference in the mean total length of the Lake Sturgeon caught, with larger sturgeon in the upstream sites and smaller sturgeon in the downstream sites, signifying a spatial segregation of life stages within the Attawapiskat River. One hundred and fifty‐four Lake Sturgeon were genotyped at 10 or more loci. There was no evidence of genetic divergence among sites or population structuring. In fact, parent‐offspring relationships were determined using COLONY between upstream and downstream sites, a minimum distance of approximately 190 rkm. This study represents the first to assess a Lake Sturgeon population systematically using a standardized index approach at multiple sites in a ‘pristine’ river. It demonstrated the importance of a holistic approach to the river at a larger scale and a better understanding of life history requirements for conservation. For example, if only one of the upper sites were assessed, it might have been interpreted as the idyllic ‘old growth’ population with limited or no recruitment. The corollary from sampling only lower sites would be identifying a lack of adults and potentially erroneously declaring an overexploitation concern. This stresses the importance of a larger scale approach for assessing ‘pristine’ rivers and not using a small scale approach to make large scale inferences.

Lake sturgeon Acipenser fulvescens populations have experienced declines throughout much of the Great Lakes. Understanding key demographic characteristics about lake sturgeon populations can help identify potential limiting factors to their recovery. Within a single spawning season, there may be multiple spawning events, which could affect genetic diversity of the resulting cohort. Our objective was to determine whether multiple discrete spawning events resulted in a larger effective number of breeders and higher genetic diversity. Larval samples were collected following the spawning periods in 2005 (n=479) and 2006 (n=279). In 2005, there were two discrete spawning events and a longer spawning season; in 2006, the spawning events were less discrete and the spawning season was shorter. Genetic samples from larval sturgeon were analyzed at 12 microsatellite loci. The effective number of breeders (N b ), genetic diversity (observed heterozygosity, expected heterozygosity, allelic richness, inbreeding coefficient), and relatedness were measured for each cohort. The effective population size (N e ) and genetic diversity were also measured in the adult population (n=85). The larval cohorts had a high N b (2005: 54; 2006: 73) relative to the N e of the adult population (N e =28). Multiple spawning events did not result in more breeders, but did result in lower relatedness among the resulting offspring. Therefore, environmental factors should be maintained that encourage an extended spawning season, increasing the likelihood of multiple spawning events and decreasing the relatedness among individuals in the cohort.