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Improving the status of endangered species can be challenging because the efficacy of conservation actions is often uncertain. Conservation aquaculture has been the main recovery action for endangered white sturgeon ( Acipenser transmontanus) in the Transboundary Reach of the upper Columbia River. Using long-term mark-recapture data (2002–2018), we predicted variation in growth rates due to genetic, environmental, and competition effects to evaluate the efficacy of the aquaculture program. Environmental conditions (by season and country) and competition had the greatest effects on growth. Growth, length-at-age, weight-at-age, and condition factor were higher for fish residing in reservoir habitats (US) compared to those in riverine habitat (Canada). Growth declined over the study period but growth in length for larger fish remained higher in the US as fish > 100 cm fork length in Canada were not growing. Small differences in growth among families indicate that differences in genetics among parents spawned in the hatchery had negligible effects on growth in the wild. Our estimate of substantive negative density-dependent growth in Canada is important for management of conservation aquaculture for sturgeons.

Total dissolved gas supersaturation (TDG) is a common issue in hydropower facilities as a result of water conveyance structures that increase the amount of air entrainment from the atmosphere and dissolved into the water. Water with TDG supersaturation can negatively impact fish, aquatic invertebrates and their habitats. This study comprehensively reviewed the physical mechanisms of TDG generation and predictive TDG generation models at various facility types. To establish TDG mitigation strategies, it is essential to develop predictive tools for TDG generation that consider both facility geometry as well as the hydrology of the downstream environment. Applications of TDG prediction at different discharge modes included plunging flows, trajectory jets, plunging jets, free-falling jets, and submerged jets were discussed. TDG transport models in downstream rivers involving mixing and dissipation were introduced, which can be integrated with TDG generation models into a platform to describe TDG distribution in river systems. Subsequently, risk ranking procedures for assessing the degree of TDG risk on fish were provided. Potential measures for mitigating TDG supersaturation were reviewed and included engineering, operational, and technical solutions. Outcomes from this review considered a diverse suite of studies on TDG issues in regulated rivers and allowed for recommendations to reduce uncertainties and improve environmental performance at facilities where TDG risks occur.

Temperature differentially influences developmental trajectories of traits during early life stages that can affect survival and recruitment. Experiments were conducted to quantify temperature-induced developmental responses of White Sturgeon (Acipenser transmontanus) yolk-sac larvae (YSL) reared at temperatures encountered across the species’ range (12.5, 14.0, 15.5, and 17.0 °C). We quantified effects of temperature on timing of transitions between sequential developmental stages from hatch to initiation of exogenous feeding. Rate of development significantly increased at warmer compared to cooler temperatures; no significant difference was observed between 15.5 and 17.0 °C or 12.5 and 14.0 °C. When standardized by relative timing of development (RTi), developmental rate was not significantly different among treatments. Morphological traits (total length; body area; yolk-sac area; head area; gill filament area; mouth area; pectoral fin area) were measured daily, though only data for YSL reared at 12.5 and 17.0 °C was used to quantify phenotypic variation. Morphological traits (excluding yolk-sac area) were generally larger 48+ hours post hatch for YSL reared at 17. 0 °C compared to 12.5 °C. In contrast, these same traits, with the exception of gill filament area, were larger in 12.5 °C reared YSL when considered as a function of developmental stage. These opposing results suggest trade-offs associated with allocating resources to a particular trait depended on rearing temperature. Our results provide the ability to estimate timing of critical early life stages (i.e., hatch, emergence) as a function of temperature which is an important management tool to understand how early life development contributes to recruitment processes and adaptability in thermally altered systems.

Spill operations of hydropower facilities can generate supersaturated total dissolved gases (TDGs) that can negatively impact fish residing in downstream habitats by causing gas bubble dise...

Gas transfer in dam spillways often leads to supersaturation of total dissolved gases (TDGs) that can cause fish mortality. Quantifying TDG associated with this process is crucial in the de...

Habitat loss is a widely recognized contributor to global declines in sturgeon populations yet habitat remediation has been limited for this highly endangered group of fish. In support of future sturgeon restoration efforts, this review examines habitat remediation needs and uncertainties. Consideration of the bio‐spatial scale of remediation identified needs ranging from local to the whole river scale. Additionally, the context of remediation ranges from reintroducing sturgeon to habitats where they have been extirpated to conservation of currently functional habitat. While multiple remediation scales and contexts are discussed, the focus on spawning and early rearing habitat and associated biological and physical monitoring reflects the range of current projects and the importance of early rearing habitats. Four case studies are presented that examine four distinct remediation contexts (mitigation, rejuvenation, re‐creation, repatriation) and three bio‐spatial scales (whole river, spawning reach, spawning location) under which remediation has been attempted. Evaluation of existing remediation works indicates that many show limited long‐term success, which is most often a response to substrate infilling in remediated habitats. Material presented in this review will help align sturgeon research and monitoring approaches in support of effective remediation. The limited number of remediation projects to‐date attests to the importance of learning from existing projects and cross‐species comparisons, to maximize the effectiveness of future restoration efforts.

In regulated rivers downstream of hydropower facilities, understanding how supersaturated total dissolved gases (TDGs) are distributed and dissipated is crucial, as they can negatively impa...

Modeling spatially explicit data provides a powerful approach to identify the effects of exogenous features associated with biological processes, including recruitment of stream fishes. However, the complex spatial and temporal dynamics of the stream and the species' reproductive and early life stage behaviors present challenges to drawing valid inference using traditional regression models. In these settings it is often difficult to ensure the spatial independence among model residuals-a key assumption that must be met to ensure valid inference. We present statistical models capable of capturing complex residual anisotropic patterns through the addition of spatial random effects within an inferential framework that acknowledges uncertainty in the data and parameters. Proposed models are used to explore the impact of environmental variables on Lake sturgeon (Acipenser fulvescens) reproduction, particularly questions about patterns in egg deposition. Our results demonstrate the need to apply valid statistical methods to identify relationships between response variables, e.g., egg counts, across locations, and environmental covariates in the presence of strong and anisotropic autocorrelation in stream systems. The models may be applied to other settings where gamete distribution or, more generally, other biotic phenomena may be associated with spatially dynamic and anisotropic processes.

Accurate estimates of the number of adults contributing to offspring (Ns), effective breeding number (Nb), and individual adult contributions to recruitment are required for recovery planning for endangered White Sturgeon Acipenser transmontanus populations, many of which are suffering from prolonged periods of recruitment failure. We show that genetic techniques can be used to characterize important features of White Sturgeon reproductive ecology in large rivers where census data are extremely difficult to obtain. We used 12 microsatellite loci and likelihood-based pedigree analysis to estimate Ns, Nb, number of kin groups (Nk), and individual reproductive success of White Sturgeon contributing to viable eggs and larvae collected in the upper Columbia River in each of 2 years. Estimated mean ±SD annual Ns was 121.5 ± 34.7, Nb was 86.5 ± 10.6, and Nk was 73.5 ± 17.3. Large variations in estimates of Ns, Nb, and Nk were observed between three spawning areas, in which one spawning site representing ...

The need for hatchery programs to reflect the latest scientific knowledge is critical for understudied groups with unique ecologies such as Acipenseriform species, including Lake Sturgeon Acipenser fulvescens. In order to address uncertainties regarding the efficacy of Lake Sturgeon culture techniques, we quantified and compared growth and survival at the egg, larval, and juvenile life history stages as a function of hatchery rearing environment over 2 years (two cohorts). Furthermore, we evaluated growth and survival of juveniles produced from three methods of progeny collection including direct gamete takes, collection of naturally spawned eggs from the stream substrate, and collection of larvae dispersing downstream from the spawning grounds. Progeny from each collection method were evenly divided between a streamside hatchery on the natal river and a traditional hatchery. Progeny reared at the streamside hatchery experienced a natural temperature regime and were exposed to natal water only fil...

Mortality during early life stages can greatly affect annual recruitment. Despite the importance to population abundance and community composition, quantitative estimates of the sources and magnitude of early life mortality in natural environments are generally lacking for many fish species. We conducted a field experiment to quantify egg mortality during incubation for Lake Sturgeon Acipenser fulvescens. Fertilized Lake Sturgeon eggs were placed in replicated exclosures in the Black River, Michigan, at a known spawning location. Incubation conditions were modified using four exclosure treatments differing in mesh size that simulated different levels of access by predators and water flow regimes (0.1–0.6 m/s). Egg mortality through 80% of the incubation period was high (average 91%) and varied significantly (75–97%) across treatments. Treatments with reduced predator access and low water velocity experienced the highest levels of cumulative egg mortality. Developmental arrest was a larger source ...

Acoustic telemetry has become a leading tool for monitoring the movements of and habitat use by many sturgeon species worldwide; however, procedures for internal tagging of small juvenile sturgeon (

Quantifying interannual variation in effective adult breeding number (N(b)) and relationships between N(b), effective population size (N(e)), adult census size (N) and population demographic characteristics are important to predict genetic changes in populations of conservation concern. Such relationships are rarely available for long-lived iteroparous species like lake sturgeon (Acipenser fulvescens). We estimated annual N(b) and generational N(e) using genotypes from 12 microsatellite loci for lake sturgeon adults (n = 796) captured during ten spawning seasons and offspring (n = 3925) collected during larval dispersal in a closed population over 8 years. Inbreeding and variance N(b) estimated using mean and variance in individual reproductive success derived from genetically identified parentage and using linkage disequilibrium (LD) were similar within and among years (interannual range of N(b) across estimators: 41-205). Variance in reproductive success and unequal sex ratios reduced N(b) relative to N on average 36.8% and 16.3%, respectively. Interannual variation in N(b)/N ratios (0.27-0.86) resulted from stable N and low standardized variance in reproductive success due to high proportions of adults breeding and the species' polygamous mating system, despite a 40-fold difference in annual larval production across years (437-16 417). Results indicated environmental conditions and features of the species' reproductive ecology interact to affect demographic parameters and N(b)/N. Estimates of N(e) based on three single-sample estimators, including LD, approximate Bayesian computation and sibship assignment, were similar to annual estimates of N(b). Findings have important implications concerning applications of genetic monitoring in conservation planning for lake sturgeon and other species with similar life histories and mating systems.

Site-specific habitat alterations have improved spawning success and early life stage survival of different fish species, including sturgeon, in regulated rivers. We modified the substrate within a section of river at the only known spawning site used by white sturgeon (Acipenser transmontanus) in the Mid Columbia River, Canada. Existing armoured riverbed conditions were modified using a mixture of larger and smaller angular rock with the assumption that the larger material would remain in place at higher discharges and help retain the smaller material. This increased substrate complexity and the amount of available interstitial spaces. We stocked 2-day posthatch larvae over both the modified site and at an adjacent control site that represented existing substrate conditions. Our objectives were to determine (i) the extent that stocked larvae remained in both the modified and control sites immediately after release, (ii) the timing of subsequent dispersal of larvae from both sites and (iii) how total length of dispersing larvae changed over time and by site. Results from this work indicated that the modified section of riverbed retained significantly higher numbers of larvae after release compared with the control site. Larvae at the modified site were able to hide and remain within the substrate and initiated downstream drift 15 days after release. With the exception of the first day after release, dispersal from both sites occurred at night. There was a significant effect of time after release and site on the total length of dispersing larvae. The larger variation in total larval length observed at the control site compared with the modified site indicated greater difficulty in hiding within the control substrate. Larvae initiated dispersal from the modified site at a mean size of 17.5 mm, which may indicate an important growth threshold before drift. Results from this work are important for future mitigative efforts for sturgeon in regulated rivers where changes to spawning substrates have occurred. Copyright © 2012 John Wiley & Sons, Ltd.

Few studies have quantified the repeatability of reproductive decisions by individuals or assessed their relationship with environmental variables over multiple seasons for long-lived iteroparous fish species. Using individual-based data collected for 678 lake sturgeon ( Acipenser fulvescens ) over 8 consecutive years, we evaluated hypotheses regarding spawning periodicity and repeatability of spawning location, spawning time, and environmental cues associated with spawning. At our study site (Upper Black River, northern Michigan, USA), interspawning interval differed between males (2.3 ± 0.08 years) and females (3.7 ± 0.16 years), but was not significantly related to age. Individual spawning behavior was highly repeatable with respect to spawning time (relative day within the spawning season) for both sexes regardless of size or age, but was less repeatable, though still significant, relative to water temperature, river discharge, and lunar phase. Breeding area was also repeatable, with individuals spawning earlier in the season selecting locations further upstream than those spawning later. Repeatability in spawning times and locations suggest that subpopulation differentiation may develop among different spawning groups, even within small and spatially contiguous areas.

Summary This paper summarizes one component of a sturgeon conservation genetics workshop held in conjunction with the Third Annual Conference of the North American Chapter of the World Sturgeon Conservation Society from 31 August through 3 September, 2010, at Chico Springs, Montana, USA. The purpose of this portion of the workshop was to foster interdisciplinary communication, help characterize sturgeon conservation and management issues and challenges, and provide the context and rationale for selecting and employing appropriate genetic investigations for sturgeon programs. Specifically, this paper: (i) provides some guiding principles for sturgeon managers and conservationists considering genetic investigations; (ii) provides a general overview of relevant analytical genetic metrics and techniques, including complications from polyploidy; and (iii) provides several examples of sturgeon conservation and management programs currently using genetic analyses for various purposes. Numerous analytical techniques are currently available to address a range of individual and population genetic issues, including population structure and status, origins and relatedness of individual fish and populations, family identity and contribution to year class, species identity and hybridization, forensic cases, and the design and evaluation of conservation and management actions. Rather than focusing on mechanistic or quantitative aspects of available genetic analyses, this paper provides a general context, overview, and several empirical examples to guide the selection of genetic analyses for sturgeon programs. We also provide information from published studies involving procedural and quantitative aspects of sturgeon genetic analyses for further reference.

Summary The feasibility of using Dual-frequency IDentification SONar (DIDSON) for monitoring white sturgeon (Acipenser transmontanus) presence and activity was tested near a known spawning area in the Columbia River, British Columbia, Canada. A fixed-station DIDSON system was deployed near the river bank adjacent to the spawning site in each 3 years (2007–2009). Fixed-station data were collected at this site in July and August each year, with an additional fixed-station site established in 2009 approximately 1.6 km upstream. A total of 267, 64, and 210 observations of sturgeon were documented based on fixed-station DIDSON sampling in 2007, 2008, and 2009, respectively. Sturgeon detections within the sample area (standardized by time and day) generally increased during late evening ⁄ early morning hours but did not appear to be related to flows. The DIDSON provided estimates of white sturgeon total lengths consistent with known length distributions for this population. Most sturgeon were detected at least 10 m away from the shoreline. These results demonstrate the feasibility of using fixed-station DIDSON for remotely monitoring white sturgeon in areas of known use. Observational data from this study also provided information on general sturgeon behaviour that is often difficult to assess with more conventional sampling methods.

Mortality that occurs during larval dispersal as a consequence of environmental, maternal, and genetic effects and their interactions can affect annual recruitment in fish populations. We studied larval lake sturgeon (Acipenser fulvescens) drift for two consecutive nights to examine whether larvae from different females exposed to the same environmental conditions during dispersal differed in relative levels of mortality. We estimated proportional contributions of females to larval collections and relative larval loss among females as larvae dispersed downstream between two sampling sites based on genetically determined parentage. Larval collections were composed of unequal proportions of offspring from different females that spawned at upstream and downstream locations (~0.8 km apart). Hourly dispersal patterns of larvae produced from females spawning at both locations were similar, with the largest number of larvae observed during 22:00–23:00 h. Estimated relative larval loss did not differ significantly among females as larvae were sampled at two sites approximately 0.15 and 1.5 km from the last section downstream of spawning locations. High inter- and intra-female variation in larval contributions and relative larval loss between nights may be a common feature of lake sturgeon and other migratory fish species, and likely is a source of inter-annual and intra-annual variation in fish recruitment.

Hatchery supplementation is widely advocated as an important means to achieve management goals of sustainable populations of lake sturgeon ( Acipenser fulvescens ). Increasing evidence for negative impacts of hatchery practices has prompted research regarding the efficacy of hatchery prescriptions that have been largely adopted from other well-studied species. Using a well-studied population in the Black River, MI drainage, we evaluated the effects of different gamete and larval collection methods and hatchery rearing environments (streamside and traditional) on measures of offspring genetic diversity estimated based on known or inferred pedigree and multi-locus genotypic data. Offspring produced from direct gamete takes (DGT) were more related (higher mean coancestry (θ) and significantly higher mean relatedness ( r xy )) than were offspring produced from collections of naturally produced eggs (NPE) from stream substrate and larvae collected while dispersing from spawning areas (DL). Pedigree and genotypic data also revealed that greater numbers of adults contributed to offspring (effective number of breeders) from DL and NPE collections than from DGT collections. Comparatively higher levels of inter-family variation in egg and juvenile mortality in the traditional hatchery rearing environment relative to the streamside rearing environment resulted in more pronounced increases in mean coancestry and decreases in effective number of breeders across sequential ontogenetic stages. Methods of gamete and offspring collection and rearing have demonstrable effects on levels of offspring genetic diversity which has significant implications for restoration of numerically depressed populations.

Summary Knowledge of age-specific survivorship is critical when developing management prescriptions for imperiled species such as the lake sturgeon (Acipenser fulvescens). Management has focused on population restoration through hatchery supplementation, largely in the absence of data about relationships between hatchery rearing conditions, size/age at release, and estimates of overwinter survival for stocked age-0 lake sturgeon. Young of the year lake sturgeon were reared from egg to age 3 months in two separate hatchery environments: a streamside hatchery on the natal Upper Black River, Michigan, and a traditional hatchery environment. From age 3 to 6 months all fish were reared in the traditional hatchery. Fish (n = 20) originating from each rearing environment were surgically implanted with ultrasonic transmitters at 6 months of age (mean total length: 31.4 cm; mean weight: 106.4 g) and released into Black Lake in December 2005. Tracking using manual and automated hydrophones was conducted during April and May 2006 to estimate overwinter survival and to test for differences in survival of fish reared in different hatchery environments. Eighteen fish (45%) were detected, 16 (40%) of which survived the winter (range of distance traveled between observations of surviving fish was 0.09–0.55 km). The remaining fish were not detected. No significant differences in survival were documented due to rearing environment or size at release. This study represents the first quantified estimate of overwinter survival for stocked age-0 lake sturgeon. The minimum estimate of 40% survival through the first winter is encouraging for hatchery programs, and will aid in the development of management prescriptions for this species.

We investigated microbial succession on lake sturgeon (Acipenser fulvescens) egg surfaces over the course of their incubation period as a function of simulated stream flow rate. The primary objective was to characterize the microbial community assembly during succession and to examine how simulated stream flow rate affect the successional process. Sturgeon eggs were reared under three flow regimes; high (0.55 m/s), low (0.18 m/s), and variable (0.35 and 0.11 m/s alternating 12 h intervals). Eggs were collected from each flow regime at different egg developmental stages. Microbial community DNA was extracted from egg surface and the communities were examined using 16S rRNA gene-based terminal restriction fragment length polymorphism and 454 pyrosequencing. Analysis of these datasets using principal component analysis revealed that microbial communities were clustered by egg developmental stages (early, middle, and late) regardless of flow regimes. 454 pyrosequencing data suggested that 90–98 % of the microbial communities were composed of the phyla Proteobacteria and Bacteroidetes throughout succession. β-Protebacteria was more dominant in the early stage, Bacteroidetes became more dominant in the middle stage, and α-Proteobacteria became dominant in the late stage. A total of 360 genera and 5,826 OTUs at 97 % similarity cutoff were associated with the eggs. Midway through egg development, the egg-associated communities of the low flow regime had a higher diversity than those communities developed under high or variable flow regimes. Results show that microbial community turnover occurred during embryogenesis, and stream flow rate influenced the microbial succession processes on the sturgeon egg surfaces.

The associations were quantified between daily and interannual variation in the timing of a closed population of lake sturgeon Acipenser fulvescens migration and arrival at spawning sites with stream environmental and lunar covariates. Spawning data were gathered from 1262 fish in Black Lake, Michigan 2001 to 2008 and by video monitoring 2000 to 2002. Sex-specific variation in responses to external cues was also tested. Results showed that a greater number of individuals initiated migration from lake to riverine habitats at dawn and dusk relative to other times of the day. Current and lagged effects of water temperature and river discharge, and periods in the lunar cycle were important variables in models quantifying movements into the river and timing of adult arrival at spawning sites. Different suites of covariates were predictive of A. fulverscens responses during different periods of the spawning season. The timing of initiation of migration and spawning, and the importance of covariates to the timing of these events, did not differ between sexes. Stream flow and temperature covaried with other variables including day length and the lunar cycle. Anthropogenic disruption of relationships among variables may mean that environmental cues may no longer reliably convey information for Acipenseriformes and other migratory fishes. © 2012 The Authors