Hydroelectric development is considered a threat to the recovery of Lake Sturgeon Acipenser fulvescens populations, in part because of injury and mortality concerns caused by interaction with hydroelectric facilities. Lake Sturgeon resident in small impoundments may be particularly susceptible to entrainment, depending on movement and habitat usage patterns. Using acoustic telemetry, we monitored coarse-scale movements of 99 juvenile, subadult and adult Lake Sturgeon captured throughout a 10-km-long hydroelectric reservoir. Overall, adults moved over larger ranges than did smaller size-classes. However, all size-classes utilized habitat immediately upstream of hydroelectric facilities, and during the 18-month study period, 27% of subadults tagged in the lowermost section of the reservoir, and 8.7% of adults tagged throughout the reservoir were entrained. Movements of juveniles and subadults were generally restricted to extended sections (2-6 km) of contiguous deepwater habitat (>15 m), and passage through the two shallow river narrows that subdivide the reservoir were rare. Over half of the tagged adults (52%) moved upstream or downstream through one or both river narrows, albeit infrequently. Initial residency influenced entrainment susceptibility for juveniles and subadults but not for adults. Results suggest that Lake Sturgeon resident in small impoundments are susceptible to entrainment. However, the presence of river narrows, which function as natural movement restrictors, may largely preclude susceptibility of juveniles and subadults resident in upstream sections.

Adaptive management and recovery initiatives for longlived, late-maturing species such as Lake Sturgeon, Acipenser fulvescens, are complicated by temporal lags. By the time anthropogenic impacts on critical periods (spawning, larval hatch, age-0 survival) would be manifested in adult populations, decades might have passed. However, recruitment patterns and population trajectory responses (both positive and negative) can be identified by examining the juvenile life stage. This study describes and evaluates a gill net method for sampling juvenile Lake Sturgeon between 250 and 800 mm fork length (FL) resident in Boreal Shield rivers in relative proportion to their abundance. The method is based on previous observations of deepwater preference (>10-15 m), and employs mesh sizes of 25.4, 50.8, 76.2, 127.0 and 152.4 mm stretched measure. Selectivity curves were generated based on 1040 Lake Sturgeon captures from six reaches of the Winnipeg and Nelson rivers, Canada. A normal (common spread) curve approximated a normal distribution centered on~390 mm FL, and relative selection exceeded 0.65 across the 250-800 mm FL range. For the Slave Falls Reservoir (Winnipeg River), Spearman's rankorder correlation (q) for zone-specific cohort-frequency distributions in adjacent sampling years ranged from 0.85 to 0.93, while the score for the entire reservoir was 0.95, suggesting inter-annual consistency. The method allows for rapid and robust assessments of relative abundance and cohort strength for juvenile Lake Sturgeon within large Boreal Shield river systems, and facilitates biological comparisons among reaches and over time. Incidentally, cohort frequency results derived herein indicate that juvenile recruitment in regulated Boreal Shield rivers can be erratic, irrespective of size of the spawning stock. Such a pattern could be an inherent characteristic of the species that needs to be accounted for when developing adaptive management and species recovery plans. U.S.

Many hydroelectric dams have been in place for 50 - >100 years, which for most fish species means that enough generations have passed for fragmentation induced divergence to have accumulated. However, for long-lived species such as Lake Sturgeon, Acipenser fulvescens, it should be possible to discriminate between historical population structuring and contemporary gene flow and improve the broader understanding of anthropogenic influence. On the Winnipeg River, Manitoba, two hypotheses were tested: 1) Measureable quantities of former reservoir dwelling Lake Sturgeon now reside downstream of the Slave Falls Generating Station, and 2) genetically differentiated populations of Lake Sturgeon occur upstream and downstream, a result of historical structuring. Genetic methods based on ten microsatellite markers were employed, and simulations were conducted to provide context. With regards to contemporary upstream to downstream contributions, the inclusion of length-at-age data proved informative. Both pairwise relatedness and Bayesian clustering analysis substantiated that fast-growing outliers, apparently entrained after residing in the upstream reservoir for several years, accounted for ~15% of the Lake Sturgeon 525–750 mm fork length captured downstream. With regards to historical structuring, upstream and downstream populations were found to be differentiated (FST = 0.011, and 0.013–0.014 when fast-growing outliers were excluded), and heterozygosity metrics were higher for downstream versus upstream juveniles. Historical asymmetric (downstream) gene flow in the vicinity of the generating station was the most logical explanation for the observed genetic structuring. In this section of the Winnipeg River, construction of a major dam does not appear to have fragmented a previously panmictic Lake Sturgeon population, but alterations to habitat may be influencing upstream to downstream contributions in unexpected ways.

Success of lake sturgeon (Acipenser fulvescens Rafinesque, 1817) stocking programmes has rarely been evaluated. As of the early 1990s, Lake Sturgeon populations were nearly extirpated from several sections of the upper Nelson River, Manitoba, at least in part due to historical overexploitation. Between 1994 and 2011, 20 885 fingerlings (age-0, untagged) and 1117 yearlings (age-1, 1014 PIT tagged) were stocked into an upper Nelson River reach. In fall 2012, a Lake Sturgeon population inventory using gill nets assessed postrelease survival/retention of stocked fish. Of 91 unique Lake Sturgeon captured, 67 (74%) possessed PIT tags, signifying they were stocked at age-1. Relative recruitment success was conservatively estimated to be 17.7 times greater for age-1 vs age-0 stocked fish based only on PIT tag recapture data. However, including 19 additional fish identified as stocked at age-1 based on atypical 'first' annuli patterns, the revised relative recruitment success rate was 130 times greater for age-1 vs age-0. An interpreted consensus ageing method produced correct age assignment 97% of the time for juveniles of known age, despite complications caused by overwinter growth in the hatchery.

Downstream passage of Lake Sturgeon Acipenser fulvescens through hydroelectric facilities is known to occur but is poorly understood. Acoustic telemetry was used to investigate downstream‐passage routes, survival, and fine‐scale movements at the Slave Falls Generating Station, located on the Winnipeg River, Manitoba. Downstream‐passage rates were estimated at 2.9% (range = 0.0–4.4%) per year for Slave Falls Reservoir adults and 21.1% (range = 19.3–22.9%) per year for subadults tagged in the lowermost section of the reservoir. No juvenile passage was observed. Lake Sturgeon movements immediately upstream of the Slave Falls Generating Station main sluiceway gates were related to bathymetric features. Fish that approached via deepwater habitat tended to abandon their downstream trajectory movements before or upon reaching the top of a relatively shallow (∼10 m depth) bedrock saddle that occurs ∼45 m upstream of the main sluiceway gates. Based on acoustic telemetry (fine‐scale tracking and presence–absence data) and supplemental information, such as trash rack spacing and spill conditions, 7 of 11 (64%) observed downstream‐passage events were concluded to have occurred via bottom‐draw regulating sluices located in the northeastern end of the powerhouse. At least 91% of the observed downstream‐passage events were survived. Results suggest that protection initiatives at hydroelectric facilities could exploit the Lake Sturgeon's bottom‐oriented nature, with bottom‐draw sluice gates likely providing a feasible way to facilitate safe downstream passage. Received June 28, 2013; accepted January 28, 2014