Lake Sturgeon Populations Research Articles

Extrinsic Factors Influencing Somatic Growth of Lake Sturgeon

AbstractVariation in somatic growth of Lake SturgeonAcipenser fulvescenshas primarily been attributed to temperature (latitude), but recent studies have suggested additional complexities. Based on populations in Manitoba, Canada, a multivariate analysis was conducted to reevaluate the extrinsic factors influencing growth of Lake Sturgeon. Length at ages 3, 6, 9, and 12 and the following six explanatory variables were examined: latitude, mean annual air temperature,pH, conductivity, juvenile Lake Sturgeon density (gill‐netCPUE), and water velocity. Length‐at‐age variables were highly correlated, but considerable variation for fish of a given age was observed along the flow axes of individual rivers (and even within multibasin reservoirs). For example, fork length at age 12 ranged from 520 to 906 mm. After dropping latitude due to colinearity with both temperature andpH, a redundancy analysis based on the remaining five explanatory variables explained 79.9% of the variation in the four length‐at‐age variables. Lake Sturgeon growth was negatively correlated with bothCPUE(41.2% of variation) and velocity (19.2%) and positively correlated with conductivity (14.8%). The temperature andpHvariables lacked statistical significance for inclusion in a forward‐selection model, regardless of which other variables were included. Our results suggest that the influence of temperature (latitude) on Lake Sturgeon growth may previously have been overstated because habitat variation was not accounted for. Indeed, because populations exploit a diversity of river types across the species range, the discussion of growth needs to be placed in the context of habitat. Individuals from two Lake Sturgeon populations occupying similar latitudes can exhibit markedly different rates of somatic growth, with much of the variation being explained by juvenile density, water velocity, and conductivity. As Lake Sturgeon recovery proceeds, fisheries managers will need to contend with dynamic growth trajectory responses to increasing abundance, much as they would for other species.

Evaluation of sea lamprey-associated mortality sources on a generalized lake sturgeon population in the Great Lakes

Abstract Lake sturgeon populations in the Laurentian Great Lakes experience two age-specific mortality sources influenced by the sea lamprey Petromyzon marinus control program: lampricide (TFM) exposure-induced mortality on age-0 fish and sea lamprey predation on sub-adults (ages 7–24). We used a generic age-structured population model to show that although lampricide-induced mortality on age-0 lake sturgeon can limit attainable population abundance, sea lamprey predation on sub-adult lake sturgeon may have a greater influence. Under base conditions, adult lake sturgeon populations increased by 5.7% in the absence of TFM toxicity if there was no change in predation; whereas, a 13% increase in predation removed this effect, and a doubling of sea lamprey predation led to a 32% decrease in adult lake sturgeon. Our estimates of lake sturgeon abundance were highly dependent on the values of life history and mortality parameters, but the relative impacts of ceasing TFM treatment and increasing predation were robust given a status quo level of predation. The status quo predation was based on sea lamprey wounding on lake sturgeon, and improvements in this information would help better define tradeoffs between the mortality sources for specific systems. Reduction or elimination of TFM toxicity on larval lake sturgeon, while maintaining TFM toxicity on larval sea lamprey, can promote lake sturgeon restoration and minimize negative impacts on other fish community members.

Over-wintering physiology of age-0 lake sturgeon (Acipenser fulvescens) and its implications for conservation stocking programs

Lake sturgeon (Acipenser fulvescens) occupy some of the most northerly distributions of any sturgeon species and experience extended overwintering periods when resources may be limited. Conservation stocking is currently used as a management tool to enhance lake sturgeon populations that are at risk or endangered. One of the most limiting components of the conservation effort is our understanding of energy requirements that allow age-0 lake sturgeon to survive their first winter. In this study, age-0 fish (mean mass 5.6 g ± 0.5 S.E.; mean total length 12.7 cm ± 0.4 S.E.) were held in groups of 12 individuals (10 total groups) and starved for a period of four weeks while being held at 1 ± 1 °C. This setting was intended to simulate winter conditions that occur in the Winnipeg River, MB, Canada. Post-winter fish condition and physiology were compared to pre-winter fish using survival, energy density, metabolic rate, glucose, triglyceride, protein, and cortisol production as metrics. While mortality was high (42%) during the experiment, results indicated that fish with total water content below 90% and energy density above 2000 J/g were more likely to survive. Whole body triglyceride, plasma triglyceride, plasma glucose levels, and standard metabolic rates were also found to significantly decline over time while whole body cortisol concentration increased. Understanding these thresholds will help in future refinements of rearing conditions, which look to improve the survival of age-0 lake sturgeon released into the wild pre-winter.

Restoration of naturally reproducing and resident riverine lake sturgeon populations through capture and transfer

The Winnebago System, Wisconsin, is home to one of the largest Lake Sturgeon Acipenser fulvescens populations in North America. Although there are >50 known spawning sites utilized by Lake Sturgeon in the 200 km of the lower Wolf River upstream of Lake Winnebago, the construction of two dams >90 years ago eliminated the ability of Lake Sturgeon to access 18.5 km of river up to their ancestral spawning grounds below Keshena Falls. Given the cultural importance of sturgeon to the Menominee Indian Tribe of Wisconsin, expanded efforts aimed at restoring Lake Sturgeon spawning and a resident population to the upper Wolf River commenced in 2011. To meet these objectives, 100 or more Lake Sturgeon per year were captured below the dams, and transferred upstream to the Wolf River within the Menominee Reservation. All transferred fish were PIT tagged and 245 fish were surgically implanted with 10 year acoustic transmitters to determine spawning locations and monitor post-release movement. The first five transfer cohorts contained 621 Lake Sturgeon, with spawning activity observed below Keshena Falls each spring following release. Gravid fish transferred within 3 weeks of spawning exhibited higher spawning rates above the upstream dam (70.2% females; 73.9% males) than gravid fish transferred in late fall (41.8% females; 41.2% males). Spawning documented below Keshena Falls and within the Red River represent the first spawning activity at these locations in >100 years. Lake Sturgeon transferred in early fall displayed higher retention rates, 2-5 years post-tagging, in the pool upstream of both dams (10.4%) compared to the late fall (3.1%) and spring transfers (7.4%). Natural reproduction was documented through capture of larval Lake Sturgeon immediately below Keshena Falls in 2013. These results demonstrate that capture and transfer can be utilized as a cost-effective and biologically-effective tool for Lake Sturgeon spawning stock and population restoration.

Divergent migration within lake sturgeon (Acipenser fulvescens) populations: Multiple distinct patterns exist across an unrestricted migration corridor.

Population structure, distribution, abundance and dispersal arguably underpin the entire field of animal ecology, with consequences for regional species persistence, and provision of ecosystem services. Divergent migration behaviours among individuals or among populations are an important aspect of the ecology of highly mobile animals, allowing populations to exploit spatially or temporally distributed food and space resources. This study investigated the spatial ecology of lake sturgeon (Acipenser fulvescens) within the barrier free Huron-Erie Corridor (HEC), which connects Lake Huron and Lake Erie of the North American Laurentian Great Lakes. Over 6years (2011-2016), movements of 268 lake sturgeon in the HEC were continuously monitored across the Great Lakes using acoustic telemetry (10years battery life acoustic transmitters). Five distinct migration behaviours were identified with hierarchical cluster analysis, based on the phenology and duration of river and lake use. Lake sturgeon in the HEC were found to contain a high level of intraspecific divergent migration, including partial migration with the existence of residents. Specific behaviours included year-round river residency and multiple lake-migrant behaviours that involved movements between lakes and rivers. Over 85% of individuals were assigned to migration behaviours as movements were consistently repeated over the study, which suggested migration behaviours were consistent and persistent in lake sturgeon. Differential use of specific rivers or lakes by acoustic-tagged lake sturgeon further subdivided individuals into 14 "contingents" (spatiotemporally segregated subgroups). Contingents associated with one river (Detroit or St. Clair) were rarely detected in the other river, which confirmed that lake sturgeon in the Detroit and St. Clair represent two semi-independent populations that could require separate management consideration for their conservation. The distribution of migration behaviours did not vary between populations, sexes, body size or among release locations, which indicated that intrapopulation variability in migratory behaviour is a general feature of the spatial ecology of lake sturgeon in unfragmented landscapes.

Habitat Quantity Required to Support Self‐Sustaining Lake Sturgeon Populations: an Alternative Hypothesis

AbstractCiting the capacity of anadromous sturgeon species to undertake lengthy spawning migrations, Auer (1996) hypothesized that a minimum of 250–300 km of barrier‐free lake and river habitat might be required to support self‐sustaining populations of Lake SturgeonAcipenser fulvescens. Twenty years later, the biological understanding of this potamodromous species has improved considerably, but there has been minimal effort to reconcile the barrier‐free hypothesis with the persistence of Lake Sturgeon populations in impounded habitats and improve the understanding of what constitutes a functional population‐level habitat unit for this species of conservation concern. Herein, POPAN mark–recapture models and sequential length‐frequency histograms were used to examine contemporary Lake Sturgeon abundance and population trajectories in three small reaches (230, 50, and 10 river kilometers [rkm]) of the Nelson and Winnipeg rivers (Manitoba), developed for hydroelectric power generation. Approximately two decades after harvest closures, results indicate that population recovery is occurring in all three reaches examined. Mechanisms other than in situ reproduction or recruitment (i.e., stocking and immigration) for increasing abundance are confidently discounted. Based on these results and other observations of contemporary persistence of Lake Sturgeon populations in impounded environments as well as recent genetic observations indicative of historical population structuring along the flow axes of naturally fragmented Boreal Shield rivers, it is contended that the barrier‐free hypothesis should no longer be cited as a “rule of thumb” with regard to the habitat quantity required to support self‐sustaining Lake Sturgeon populations. Rather, the concept of an uninterrupted “spawn–drift–settle–establish” habitat sequence as the cornerstone of a functional population‐level habitat unit may have broader relevance to species recovery initiatives and management. Given appropriate geomorphologic and hydraulic conditions, Lake Sturgeon populations can thrive—and in Boreal Shield rivers likely have for thousands of years—in lake, river, or impoundment sections as small as 10 rkm.

Rethinking the influence of hydroelectric development on gene flow in a long-lived fish, the Lake Sturgeon Acipenser fulvescens.

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.

Status of Lake Sturgeon (Acipenser fulvescensRafinesque 1817) in North America

Summary Lake Sturgeon is a potamodromous, fluvial-dependent species from the family Acipenseridae, and one of the largest freshwater fishes within its North American range extending to the Great lakes, Mississippi River, and Hudson Bay drainages. Like almost all other sturgeon species, Lake Sturgeon populations throughout its range suffered mass declines or extirpation in the late 1800s into the early 1900s, due to extensive overexploitation and habitat loss and alteration. However, Lake Sturgeon are still present in low to high densities throughout their native range due primarily to factors including: the species long life span and resiliency, the remote location of many northern populations, long-term pro-active management programs effectively controlling exploitation, improved habitat and water-quality conditions, and recovery programs that have been in effect since the late 1970s. Recovery programs initiated in the late 1970s are now just beginning to show signs of natural recruitment from populations re-built with stocked fish. Large sustainable recreational Lake Sturgeon fisheries with annual harvests of up to 45 000 kg and a commercial fishery with an annual harvest of up to 80 000 kg still exist and are maintained for Lake Sturgeon due primarily to rigid regulations, harvest controls, enforcement, and user involvement. The prognosis for the species is generally good, although habitat loss and maintaining public interest in the species management and recovery continue to be the greatest threats to local and regional populations. Hydropower development, especially in the northern part of the species’ range, is especially challenging due to the potential negative impact this type of development can have on a long migrating fish like Lake Sturgeon. Advances in understanding Lake Sturgeon life history, habitat requirements, and distribution within and among water systems has strongly indicated that dams and Lake Sturgeon can co-exist, if the correct planning and necessary mitigative techniques are employed at each site on a case-by-case basis.

In situ assessment of lampricide toxicity to age-0 lake sturgeon

Abstract The lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and 2′, 5-dichloro-4′-nitrosalicylanilide (niclosamide) are used to control sea lamprey (Petromyzon marinus), an invasive species in the Great Lakes. Age-0 lake sturgeon (Acipenser fulvescens), a species of conservation concern, share similar stream habitats with larval sea lampreys and these streams can be targeted for lampricide applications on a 3- to 5-year cycle. Previous laboratory research found that lake sturgeon smaller than 100 mm could be susceptible to lampricide treatments. We conducted stream-side toxicity (bioassay) and in situ studies in conjunction with 10 lampricide applications in nine Great Lakes tributaries to determine whether sea lamprey treatments could result in in situ age-0 lake sturgeon mortality, and developed a logistic model to help predict lake sturgeon survival during future treatments. In the bioassays the observed concentrations where no lake sturgeon mortality occurred (no observable effect concentration, NOEC) were at or greater than the observed sea lamprey minimum lethal concentration (MLC or LC99) in 7 of 10 tests. We found that the mean in situ survival of age-0 lake sturgeon during 10 lampricide applications was 80%, with a range of 45–100% survival within streams. Modeling indicated that in age-0 lake sturgeon survival was negatively correlated with absolute TFM concentration and stream alkalinity, and positively correlated with stream pH and temperature. Overall survival was higher than expected based on previous research, and we expect that these data will help managers with decisions on the trade-offs between sea lamprey control and the effect on stream-specific populations of age-0 lake sturgeon.

Sensitivity of lake sturgeon (Acipenser fulvescens) early life stages to 2,3,7,8-tetrachlorodibenzo-P-dioxin and 3,3',4,4',5-pentachlorobiphenyl.

The aquatic food web of the Great Lakes has been contaminated with polychlorinated biphenyls (PCBs) since the mid-20th century. Threats of PCB exposures to long-lived species of fish, such as lake sturgeon (Acipenser fulvescens), have been uncertain because of a lack of information on the relative sensitivity of the species. The objective of the present study was to evaluate the sensitivity of early-life stage lake sturgeon to 3,3',4,4',5-pentachlorobiphenyl (PCB-126) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure. Mortality, growth, morphological and tissue pathologies, swimming performance, and activity levels were used as assessment endpoints. Pericardial and yolk sac edema, tubular heart, yolk sac hemorrhaging, and small size were the most commonly observed pathologies in both TCDD and PCB-126 exposures, beginning as early as 4 d postfertilization, with many of these pathologies occurring in a dose-dependent manner. Median lethal doses for PCB-126 and TCDD in lake sturgeon were 5.4 ng/g egg (95% confidence interval, 3.9-7.4 ng/g egg) and 0.61 ng/g egg (0.47-0.82 ng/g egg), respectively. The resulting relative potency factor for PCB-126 (0.11) was greater than the World Health Organization estimate for fish (toxic equivalency factor = 0.005), suggesting that current risk assessments may underestimate PCB toxicity toward lake sturgeon. Swimming activity and endurance were reduced in lake sturgeon survivors from the median lethal doses at 60 d postfertilization. Threshold and median toxicity values indicate that lake sturgeon, like other Acipenser species, are more sensitive to PCB and TCDD than the other genus of sturgeon, Scaphirhynchus, found in North America. Indeed, lake sturgeon populations in the Great Lakes and elsewhere are susceptible to PCB/TCDD-induced developmental toxicity in embryos and reductions in swimming performance. Environ Toxicol Chem 2017;36:988-998. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Documentation of lake sturgeon (Acipenser fulvescensRafinesque, 1817) recovery and spawning success from a restored population in the Mississippi River, Missouri, USA

Lake sturgeon Acipenser fulvescens are considered rare and were nearly extirpated in the Mississippi River in Missouri by 1931 as a result of overfishing and habitat fragmentation. Propagation efforts have been implemented by the Missouri Department of Conservation since 1984 as means to restore the lake sturgeon population. Although recent population increases have been observed, a formalized evaluation to determine if lake sturgeon are self-sustaining in the Missouri portion of the Mississippi River has not been completed. Therefore, the objectives of this study were to: (i) determine the proportion of reproductive individuals, (ii) evaluate seasonal movement patterns of adults, and (iii) validate purported spawning locations within the Mississippi River in Missouri. Lake sturgeon catch data indicated that approximately 11 percent of the population are reproductively mature. Additionally, telemetry data confirms that the greatest movement by adult lake sturgeon occurs during spring, which suggests spawning behavior. Finally, it was possible to document lake sturgeon embryos and emergent fry larvae below Melvin Price Locks and Dam 26 in the Upper Mississippi River near St. Louis, Missouri. Water velocity, depth, and substrate size were measured at this location and embryos were collected and hatched in the laboratory. River gage data suggest that spawning behavior may have been elicited by a large influx of water during a drawdown period of water above the dam. This study represents the first documented spawning of A. fulvescens in the Mississippi River and highlights the success of recovery efforts in Missouri.

Stable isotope characterization of Rainy River, Ontario, lake sturgeon diet and trophic position

Abstract Lake sturgeon ( Acipenser fulvescens ) are considered threatened and many populations have declined since the early 1890s. Limited food web studies have been conducted with lacustrine lake sturgeon populations while similar studies do not exist for riverine populations. We use stable isotope analysis to study the diet composition of lake sturgeon captured in the Rainy River, Ontario. Historical reports of lake sturgeon consumption of fish and fish eggs exist, but both prey have largely been considered as a minor contribution to the overall diet of lake sturgeon. More recent dietary studies have focused on juvenile sturgeon and report low or no incidence of fish or fish eggs in lake sturgeon diets. The results of the stable isotope studies of Rainy River lake sturgeon suggest they obtain a large portion of their energy from organic material derived directly or indirectly from fish. Results parallel those recently reported for adult sturgeon in Lake Winnebago, Wisconsin, and are important in the context of contributing modern technical verification to earlier historical reports of fish and fish eggs in lake sturgeon diets. The results of this study provide evidence of potential seasonal or temporal shifts in lake sturgeon diet and further evidence to the potential shift in resource use based on life stage. Estimates of isotopic niches for the Rainy River sturgeon establish an important baseline for future changes in food web structure that might accompany the introduction of invasive species or the addition of anthropogenic stressors that could have implications for lake sturgeon conservation.

Validation of a spatial model used to locate fish spawning reef construction sites in the St. Clair–Detroit River system

Lake sturgeon (Acipenser fulvescens) populations have suffered precipitous declines in the St. Clair–Detroit River system, following the removal of gravel spawning substrates and overfishing in the late 1800s to mid-1900s. To assist the remediation of lake sturgeon spawning habitat, three hydrodynamic models were integrated into a spatial model to identify areas in two large rivers, where water velocities were appropriate for the restoration of lake sturgeon spawning habitat. Here we use water velocity data collected with an acoustic Doppler current profiler (ADCP) to assess the ability of the spatial model and its sub-models to correctly identify areas where water velocities were deemed suitable for restoration of fish spawning habitat. ArcMap 10.1 was used to create raster grids of water velocity data from model estimates and ADCP measurements which were compared to determine the percentage of cells similarly classified as unsuitable, suitable, or ideal for fish spawning habitat remediation. The spatial model categorized 65% of the raster cells the same as depth-averaged water velocity measurements from the ADCP and 72% of the raster cells the same as surface water velocity measurements from the ADCP. Sub-models focused on depth-averaged velocities categorized the greatest percentage of cells similar to ADCP measurements where 74% and 76% of cells were the same as depth-averaged water velocity measurements. Our results indicate that integrating depth-averaged and surface water velocity hydrodynamic models may have biased the spatial model and overestimated suitable spawning habitat. A model solely integrating depth-averaged velocity models could improve identification of areas suitable for restoration of fish spawning habitat.

Genetic effects of habitat restoration in the Laurentian Great Lakes: an assessment of lake sturgeon origin and genetic diversity

Lake sturgeon (Acipenser fulvescens) have experienced significant habitat loss, resulting in reduced population sizes. Three artificial reefs were built in the Huron‐Erie corridor in the Great Lakes to replace lost spawning habitat. Genetic data were collected to determine the source and numbers of adult lake sturgeon spawning on the reefs and to determine if the founder effect resulted in reduced genetic diversity. DNA was extracted from larval tail clips and 12 microsatellite loci were amplified. Larval genotypes were then compared to 22 previously studied spawning lake sturgeon populations in the Great Lakes to determine the source of the parental population. The effective number of breeders (Nb) was calculated for each reef cohort. The larval genotypes were then compared to the source population to determine if there were any losses in genetic diversity that are indicative of the founder effect. The St. Clair and Detroit River adult populations were found to be the source parental population for the larvae collected on all three artificial reefs. There were large numbers of contributing adults relative to the number of sampled larvae. There was no significant difference between levels of genetic diversity in the source population and larval samples from the artificial reefs; however, there is some evidence for a genetic bottleneck in the reef populations likely due to the founder effect. Habitat restoration in the Huron‐Erie corridor is likely resulting in increased habitat for the large lake sturgeon population in the system and in maintenance of the population's genetic diversity.

Egg and Larval Development Index for Lake Sturgeon

AbstractWe developed an index of egg and larval maturation for Lake Sturgeon Acipenser fulvescens to incrementally chart development over time. To evaluate the relationship between temperature and development rate, eggs and larvae from the Wolf River were incubated at four constant water temperatures. The time required for neural tube closure, hatch, and exogenous feeding were monitored. The number of hours from incubation to each development stage and mean water temperature were related by predictive exponential regression equations for neural tube closure (R2 = 0.96), start hatch (R2 = 0.97), end hatch (R2 = 0.97), and exogenous feeding (R2 = 0.99). Calculated hourly development was used to create an index capable of predicting specific daily development. Daily development from incubation to exogenous feeding ranged from 2.0% to 8.3% at 10°C to 19.9°C. This index was used to predict the rate of development of sturgeon eggs and larvae from the St. Lawrence River reared in water with varying temperatures. All development stages occurred within 24 h of the time predicted by the index. This index may be used to accurately predict and manipulate the progress of development and assist with the culture and management of Lake Sturgeon populations.

Review of a species in peril: what we do not know about lake sturgeon may kill them

Lake sturgeon are arguably the largest and most unique freshwater fish in North America. Unfortunately their uniqueness includes many characteristics that make them especially vulnerable to anthropogenic impacts including overfishing, habitat fragmentation, and degradation. For approximately 100 years lake sturgeon populations across North America have either been in decline and (or) have experienced a sluggish recovery. While this is partly due to lake sturgeon life history, most researchers agree that habitat fragmentation and degradation are currently the highest risk to the species. Though most lake sturgeon populations are depressed, there are a few exceptions that offer a glimpse into what a stable population or recovery may look like. The following review highlights such instances as well as what is known and more importantly what is not known about this unique species. Specifically, we highlight the need for improved and organized sharing of raw data given the fact that many researchers do not have access to the plethora of information available to others (e.g., otoliths for aging). We examine the varying life history and diet choices of this plastic species offering hypotheses for differences in migration routes and distances as well the differing recovery rates found across their range. We highlight myths about the species providing evidence that they may not be as long lived and fecund as previously thought. We examine the lake sturgeon’s current legal status across North America including the efforts of nonprofit groups that have had success in increasing population numbers. Most importantly, we highlight logistical problems faced by researchers and data gaps in the literature that must be filled to increase the odds of a successful recovery. Alongside the data gaps, the recovery of this species is fraught with political and industrial road blocks that are as varied as its current recovery. Subsequently, as is the case with many species, its survival will come down to solid scientific knowledge and the value placed on it by society.

Verifying success of artificial spawning reefs in the St. Clair-Detroit River System for lake sturgeon (Acipenser fulvescens Rafinesque, 1817)

Summary Lake sturgeon (Acipenser fulvescens) were historically abundant in the St. Clair – Detroit River System (SCDRS), a 160 km river/channel network. In the SCDRS, lake sturgeon populations have been negatively affected by the loss/degradation of natural spawning habitat. To address habitat loss for lake sturgeon and other species, efforts are underway to restore spawning substrate by constructing artificial reefs. The main objective of this study was to conduct post-construction monitoring of lake sturgeon egg deposition and larval emergence near two of these artificial reefs: Fighting Island Reef (FIR) in the Detroit River, and Middle Channel Reef in the St. Clair River. An additional site in the St. Clair River where lake sturgeon spawn on a coal clinker bed was also investigated. From 2010 to 2012, viable eggs and larvae were collected from all of these reefs, indicating that conditions are suitable for egg deposition, incubation, and larval emergence. In the St. Clair River, the results indicate the likelihood of other spawning sites upstream of these artificial reef sites.

Relative recruitment success of stocked age-1 vs age-0 lake sturgeon (Acipenser fulvescens Rafinesque, 1817) in the Nelson River, northern Canada

Summary 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 post-release 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.

Identification of a robust Lake Sturgeon (Acipenser fulvescens Rafinesque, 1917) population in Goulais Bay, Lake Superior

Summary Lake Sturgeon (Acipenser fulvescens Rafinesque, 1917) in Lake Superior are greatly depressed from their historic abundance, and few populations meet the rehabilitation goals identified by management agencies. A netting program targeting juvenile Lake Sturgeon (ages 3–15) was implemented from 2010 to 2012 in Goulais Bay, a shallow, productive bay in the south-eastern part of the lake, to determine abundance, distribution, population characteristics (size structure, condition, age structure, mortality and growth), and recruitment patterns. Five-hundred and thirty-one individuals were captured over the 3-year study, resulting in a mark-recapture estimate of 4977 (95% CIs 3295–7517) juveniles. Catch rates in this study were higher than in any other location in Lake Superior, with sturgeon being broadly distributed around the bay. Estimated annual survival rate ranged from 0.691 to 0.858, depending on the method used. The majority of fish captured were between 620 and 800 mm in total length and were between 4 and 10 years of age (range 1–29 years). Recruiting year-classes were apparent every year, with no apparent effects due to lampricide treatments (a suspected threat to age-0 Lake Sturgeon) in the Goulais River. Year-class strength was positively related to spring water levels. It is possible that this robust Goulais Bay population could help re-populate the south-eastern part of Lake Superior, which contains a number of large, productive embayment areas that formerly supported large Lake Sturgeon populations.

The effect of multi-year vs single-year stocking on lake sturgeon (Acipenser fulvescens Rafinesque, 1817) genetic diversity

Summary Many lake sturgeon (Acipenser fulvescens Rafinesque, 1817) populations in the Great Lakes have not recovered from previous threats, whereby stocking can increase population abundances. Stocking in Oneida Lake, New York used two approaches: single-year stocking using sturgeon from the Des Prairies River and multi-year stocking using sturgeon from the St. Lawrence River. Stocked A. fulvescens were sampled and assigned to their corresponding stocking strategy based on age. Samples were analyzed at 12 microsatellite loci to evaluate how a single year of stocking (N = 273) and multiple years of stocking (N = 100) affected genetic diversity and effective population size (Ne). Single-year stocking resulted in lower genetic diversity, likely due to a small number of parents. Multi-year stocking retained most of the genetic diversity of the source population, compensating for the few parents available in a single year. Although multi-year stocking resulted in a higher Ne, the Ne:N ratio was lower (0.34) compared to single-year stocking (0.65), likely due to unequal sex ratios and family size variance across years. It is recommended that stocking of Lake Sturgeon take place over several years. However, consistent numbers need to be stocked each year and family size should be equalized across cohorts in order to maximize Ne.