Diet differences between wild and stocked age-0 to age-3 lake trout indicate influence of early rearing environments

Wild lake trout recently began to appear in abundance in Lake Champlain after over 40 years of stocking, providing an opportunity to compare the seasonal diet of wild and stocked juveniles. We sampled 2,349 age-0 to age-3 lake trout collected in bottom trawls from April to November 2015–2018, and examined the relationship between diet and spatial heterogeneity in abundance of wild and stocked juveniles. Stocked fish were, on average, the size of wild fish one year older. Wild juveniles had fewer empty stomachs and more items per stomach than stocked fish at each age. Mysis diluviana dominated the diet of age-0 and age-1 wild lake trout until they began to consume fish in fall at age-1. In contrast, the diet of newly-stocked fish (age-1) comprised rainbow smelt (Osmerus mordax), slimy sculpin (Cottus cognatus), alewife (Alosa pseudoharengus), with Mysis only abundant in summer and fall. Number and composition of diet items varied among geographic areas of the lake but did not explain differences in abundance of wild or stocked fish by area. Diet overlap was high between wild and stocked fish for each age class at each season, except in fall at age-0. Differences in the diet of wild and stocked juveniles likely reflect effects of early rearing experience. Recruitment of wild lake trout depends on availability and abundance of Mysis, but our diet data do not provide insight to explain why recruitment is finally occurring after a protracted delay.     

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

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.     

Multi-year evidence of unbiased sex ratios in hatchery and wild-reared age-0 lake sturgeon (Acipenser fulvescens)

Assessment of population sex ratios allows managers to forecast recruitment dynamics and loss of genetic diversity in natural populations and is important when the focal population is in low abundance and subject to demographic stochasticity. If levels of natural or artificial selection differ for males and females and levels of mortality likewise vary, lower levels of population recruitment, loss of genetic diversity, and genetic drift can occur. Lake sturgeon (Acipenser fulvescens) are a species of conservation concern, where restoration efforts increasingly rely on hatchery supplementation. Raising larvae to the juvenile stage can increase survival during important early life stages; however, knowledge is lacking concerning effects of artificial rearing environments on differential sex-specific survival before release. We genetically determined the sex of 1459 age-0 lake sturgeon from three cohorts (2016 through 2018) using PCR assays of the ALLWSex2 acipenserid sexing marker. Sexed individuals represented three groups: (1) wild-captured dispersing larvae that died during hatchery rearing, (2) wild-captured dispersing larvae that survived hatchery rearing to release, and (3) wild-captured, wild-raised age-0 individuals. Sex ratios of wild-captured larvae (dead + live) were nearly 50:50 in all years surveyed. We observed slight, but non-significant, directionality in sex ratios in the live and dead hatchery-reared larvae and in wild-captured age-0 individuals. Genetic sexing methods allow for analyses during prolonged pre-reproductive periods and associated variable environmental and demographic circumstances, in situations where physical determination of sex is not possible.     

Molecular sexing of lake sturgeon

Demographic data including characterizations of population sex and age composition are of fundamental importance for effective management, especially for numerically depressed Great Lakes populations of imperiled species such as lake sturgeon (Acipenser fulvescens). The goal of this paper was to extend a recently reported Acipenserid-derived PCR-based genotyping test to determine sex of lake sturgeon. We demonstrate that the recently reported AllWSex2 primers amplified the female sex-specific region in lake sturgeon of known sex, consistent with a ZZ/ZW mode of inheritance. Sanger sequencing of female lake sturgeon PCR products matched published sequences from female sterlet (Acipenser ruthenus), showing 100% query cover and 98% (63/64) identity. The ability to provide a rapid, cost-effective, and unambiguous determination of sex for lake sturgeon will allow managers to determine compositional estimates of sex ratios during any season, and for individuals at any age or size, which is of great utility for species characterized by delayed sexual maturity and lacking external sexual dimorphisms.     

Genetic assessment of straying rates of wild and hatchery reared lake sturgeon (Acipenser fulvescens) in Lake Superior tributaries

Natal philopatry in lake sturgeon (Acipenser fulvescens) has been hypothesized to be an important factor that has lead to genetically distinct Great Lakes populations. Due to declining abundance, population extirpation, and restricted distribution, hatchery supplementation is being used to augment natural recruitment and to reestablish populations. If hatchery-reared lake sturgeon are more likely to stray than naturally produced individuals, as documented in other well-studied species, outbreeding could potentially jeopardize beneficial site-specific phenotypic and genotypic adaptations. From 1983 to 1994, lake sturgeon propagated using eggs taken from Lake Winnebago adults (Lake Michigan basin) were released in the St. Louis River estuary in western Lake Superior. Our objective was to determine whether these introduced individuals have strayed into annual spawning runs in the Sturgeon River, Michigan. Additionally, we estimated a natural migration rate between the Sturgeon River and Bad River, Wisconsin populations. Presumed primiparous lake sturgeon sampled during Sturgeon River spawning runs from 2003 to 2008 were genotyped at 12 microsatellite loci. Genotypic baselines established for the Sturgeon River (n = 101), Bad River (n = 40), and Lake Winnebago river system (n = 73) revealed a relatively high level of genetic divergence among populations (mean F_ST = 0.103; mean R_ST = 0.124). Likelihood-based assignment tests indicated no straying of stocked Lake Winnebago strain lake sturgeon from the St. Louis River into the Sturgeon River spawning population. One presumed primiparous Sturgeon River individual likely originated from the Bad River population. Four first-generation migrants were detected in the Sturgeon River baseline, indicating an estimated 3.5% natural migration rate for the system.     

Application of a Depletion-Based Stock Reduction Analysis (DB-SRA) to lake sturgeon in Lake Erie

Lake Erie supported the greatest yield of lake sturgeon within the Laurentian Great Lakes near the end of the 19th century with >2000 metric tons caught at the peak of the fishery. The fishery collapsed by the 1920s when <1% of the previous peak catch was removed. Despite closures of the fishery, lake sturgeon remain rare in Lake Erie. We applied a depletion-based stock reduction analysis (DB-SRA) to the catch of lake sturgeon from 1879 to 1929 to gain estimates of sustainable fishery reference points and the historic carrying capacity of Lake Erie for lake sturgeon. We also simulated population growth of lake sturgeon from 1929 to the present with varying assumptions of the current carrying capacity of the lake. The estimated historic carrying capacity of lake sturgeon was 22,652 metric tons. During the height of the fishery, exploitation was as high as 37% which was more than an order of magnitude greater than that required for maximum sustainable yield. Projections of the population from 1929 to 2016 suggest sufficient time has passed since the collapse of the fishery that the population should have recovered to levels that would support a fishery at maximum sustainable yield. However, lake sturgeon remain rare in Lake Erie indicating that other factors such as habitat availability may be limiting their recovery. Our estimates of carrying capacity will be informative when setting recovery targets which consider the amount of habitat loss.     

Multi-run migratory behavior of adult male lake sturgeon in a short river

Lake sturgeon (Acipenser fulvescens) can migrate long distances to spawn, but many populations currently spawn in systems where the length of accessible riverine migratory habitat has been greatly reduced by dam construction. With the increased prevalence of shortened rivers, focusing on migratory dynamics in short rivers (<30 km) is beneficial to understanding the migratory needs of lake sturgeon populations. Here we document male lake sturgeon movements during the spawning period in the Winooski River, Vermont, USA; a river with only 17 km to the first natural upstream barrier. Male lake sturgeon were acoustically tagged (n = 25, 1215–1470 mm TL) and tracked using five to nine stationary receivers from 2017 to 2019. River discharge, temperature, the lagged effect of temperature (3-day), and time of day were significant factors describing upstream movements of tagged fish. Migrating male lake sturgeon (n = 10 in 2017, n = 18 in 2018, and n = 17 in 2019) displayed general movement patterns during the spawning period that included a single run upstream to the spawning site (60%), upstream and downstream movements throughout the river during the season (20%), or multiple runs made up the entire length of the spawning tributary to the spawning site (20%). No multi-run males were observed during 2018 when discharge was less flashy (i.e., fewer steep increases and declines in discharge) than in 2017 and 2019. These results suggest that the prevalence of multi-run spawning behavior of male lake sturgeon is related to flow conditions.     

A hydrodynamics-based framework to evaluate the impact of fishways on drifting lake sturgeon larvae

Lake sturgeon (Acipenser fulvescens) have recently been a target for conservation in the Laurentian Great Lakes. While improving spawning success has been a major goal of these efforts, an often-overlooked component is the survival of the larvae after hatching, during the period of downstream drift. In a dammed river system, during this phase, larvae may need to drift past dam infrastructure. This journey past dams often results in an increase in larval mortality for a variety of reasons, including exposure to highly turbulent flow. Quantifying the aspects of turbulence related to larval mortality within fishways will inform retrofitting or future design efforts of fishways to improve larval viability. This study uses dimensional arguments to characterize the flow conditions influencing larval viability through fishways. One such condition discussed here is strain rate, which can be used as a diagnostic basis to determine candidate fishways for conservation measures. Based on Kolmogorov’s theory (1941), the strain rate present in the fishway at the pertinent scale for lake sturgeon larvae, S_η, can be estimated using the fishway’s macroscale Reynolds number Re, the relevant macroscale fishway velocity U, and the smallest fishway pool dimension l_e as S_ηl_e/U ≈ Re^1/2. This approach is illustrated in the case of the Vianney-Legendre Fishway in Québec, and determined this fishway to be potentially hazardous to drifting lake sturgeon larvae.     

Evaluation of 3-trifluoromethyl-4-nitrophenol (TFM) residues following a lampricide treatment as a risk assessment to the endangered piping plover

To evaluate the risk to the federally endangered piping plover (Charadrius melodus) from exposure to 3-trifluoromethyl-4-nitrophenol (TFM) during a sea lamprey control treatment we collected and analyzed a series of water, sediment, and aquatic invertebrate samples for the presence of TFM before, during, and after treatment of the Little Two Hearted River, Luce County, Michigan in July 2008. Results of the analyses in water showed the treatment resulted in a maximum concentration of 1.14 mg/L TFM. Residues of TFM in water were greatest 50 m east of the mouth (0.73 mg/L TFM) and had decreased below detection at most of the sampling sites one day after treatment. Residues of TFM in sediment were greatest 50 m east of the mouth (105 ng/g TFM) with lower levels observed west of the mouth (3-5 ng/g TFM) the day of the treatment. Residues decreased rapidly and were below detection in most of the samples the day after treatment. Residues of TFM in caged mayflies were greatest one day after treatment (3,193 ng/g wet weight), decreased substantially by 4 days after treatment (74 ng/g), but were still present 8 days after treatment (80 ng/g). Based on results from this study the overall TFM exposure to adult piping plovers (0.425 mg/kg) was 85 times less than the estimated No Observable Effects Concentration (NOEC) of 36 mg/kg and was 17 times less than the NOEC for plover chicks (2.13 mg/kg) indicating the risk from sea lamprey control operations would likely be minimal.     

Foraging mechanisms of age-0 lake trout (Salvelinus namaycush)

Reaction distances under various light intensities (0-19 uE/m2/s), angles of attack, swimming speeds, and percentage of overall foraging success were measured. Extensive efforts have been invested in restoring lean lake trout (Salvelinus namaycush) populations in the Laurentian Great Lakes, but successful natural recruitment of lake trout continues to be rare outside of Lake Superior and parts of Lake Huron. There is evidence of high mortality during the first several months after eggs hatch in the spring, but little is known about the foraging mechanisms of this age-0 life stage. We developed a foraging model for age-0 lake trout (S. namaycush) in response to amphipods (Hyalella azteca) and mysids (Mysis diluviana) by simulating underwater environmental conditions in the Great Lakes using a temperature-controlled chamber and spectrally matched lighting. Reaction distances under various light intensities (0–19 uE/m²/s), angles of attack, swimming speeds, and percentage of overall foraging success were measured. Intake rates under different light intensities and prey densities were also measured. Age-0 lake trout were non-responsive in the dark, but were equally responsive under all light levels tested. Age-0 lake trout also demonstrated a longer reaction distance in response to moving prey, particularly mysids, which had an escape response that reduced overall foraging success. We determined that prey intake rate (numeric or biomass) could be modeled most accurately as a function of prey density using a Michaelis–Menton equation and that even under low mysid densities (3 individuals/m²), age-0 lake trout could quickly satisfy their energetic demands in a benthic setting.     

Acute toxicity of the lampricides TFM and niclosamide: Effects on a vascular plant and a chironomid species

The lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide have been used for about 60 years to control sea lamprey (Petromyzon marinus) in the Great Lakes Basin and Lake Champlain. To register these chemicals as pesticides in North America, their environmental effects must be reviewed on a periodic basis. As a part of this effort, toxicity of TFM and niclosamide to duckweed (Lemna gibba), and of niclosamide to aquatic midge (Chironomus dilutus), was assessed. Results of these studies indicate that for both lampricides, the no observed and lowest observed effect concentrations (NOEC and LOEC) exceed expected environmental concentrations, with effects only in the highest concentrations tested and the longest exposure times. Duckweed exposed to TFM indicated 7-day LOECs ≥4.88 mg/L for mean specific growth rate and yield, with the half maximal effective concentration (EC₅₀) > 9.74 mg/L. For duckweed exposed to niclosamide, 7-day LOECs for mean specific growth rate and yield ranged from 0.271 to 0.569 mg/L, with the half maximal inhibitory concentration (IC₅₀) 0.725 mg/L or greater depending on the parameter measured. For midge larvae exposed to niclosamide-dosed sediment, the LOEC values based on survival and growth were 26.2 mg/kg and >82.1 mg/kg, respectively, and the EC₅₀ based on survival was 49.6 mg/kg. Based on these data, deleterious effects on aquatic plants and benthic invertebrates are unlikely to result from use of TFM and niclosamide for lamprey control, given that the effect concentrations are in excess of the expected environmental concentrations.     

Genetic origins and diversity of lake sturgeon in the St. Louis River Estuary

Lake sturgeon Acipenser fulvescens were extirpated from the St. Louis River Estuary (SLRE) by the early 1900’s due to overfishing and habitat degradation. A restoration stocking program began in 1983, and continued almost annually until 2000. Lake sturgeon stocked into the SLRE were primarily obtained from the Wolf River (Lake Winnebago) genetic stock (n = 861,000) but some sturgeon were obtained from the Sturgeon River (Lake Superior) genetic stock (n = 61,380). Recently, spawning and natural recruitment has been documented near the Fond du Lac Dam, the upstream limit for lake sturgeon migrating from Lake Superior. However, the genetic origin of lake sturgeon spawning in the SLRE was unknown. Our objectives were to determine (1) the genetic origins and (2) genetic diversity of lake sturgeon spawning in the SLRE. Using both GENECLASS2 and ONCOR, a majority (79–81%) of lake sturgeon captured in the SLRE during spawning (2016–2018) assigned to the Wolf River genetic stock (Lake Winnebago) with greater than 80% probability using established microsatellites and a standardized genetic baseline. Other genetic stocks present (≥1%) included the Pic and Goulais rivers and possibly the Black Sturgeon River (identified using GENECLASS2, but not ONCOR); no fish assigned to the Sturgeon River using either method. Genetic diversity metrics showed that the SLRE lake sturgeon population was similar to other Lake Superior lake sturgeon populations. Overall, the SLRE Sturgeon population appears headed towards recovery. Adaptive management practices currently being employed should be continued to help guide further recovery of this population.     

A review of lake sturgeon Acipenser fulvescens spawning sites in the Lower St. Lawrence and Ottawa river systems

Knowledge concerning critical habitats such as spawning sites is crucial to the preservation of vulnerable fish species like sturgeons. For lake sturgeon Acipenser fulvescens populations in the Lower St. Lawrence and Ottawa river systems, knowledge about spawning sites has been documented primarily in the grey literature, unpublished reports, or notes, with very little published in peer-reviewed literature. Here, we reviewed over 100 reports, articles, and unpublished observations in the Lower St. Lawrence and Ottawa river systems to synthesize available information concerning the location of lake sturgeon spawning sites, the level of spawning activity, and the methodologies used for assessments. In this review, 38 lake sturgeon spawning sites were identified. Of these sites, 11 were enhanced or artificially created for lake sturgeon. In the Lower St. Lawrence River, 68% of known spawning sites were located downstream from a dam compared to 47% in the Ottawa River. The use of the two artificially created spawning sites in the Lower St. Lawrence River has not yet been confirmed, while one site established in the Ottawa River has had confirmed spawning activity, although the spawning run size is unknown. In contrast, spawning has been confirmed for the seven natural spawning sites that have been artificially expanded in these systems, and two of these sites have large spawning runs. Information revealed by this review suggests that lake sturgeon populations in these large river systems rely on multiple spawning sites and that expanding natural spawning grounds may be more effective than creating new ones.     

Diel timing of lake sturgeon (Acipenser fulvescens) activity revealed by satellite tags in the Laurentian Great Lake Basin

Lake sturgeon (Acipenser fulvescens) are slow-growing and long-lived residents of the Laurentian Great Lakes Basin, making them vulnerable to anthropogenic stressors. The behavior of lake sturgeon, and how it may result in conflict with human activities, remain incompletely understood. Our goal was to describe how environmental conditions, such as depth, temperature, and time of day, influence lake sturgeon activity. Data were recorded using pop-up archival satellite tags, which have provided insight into the ecology, physiology, and behavior of challenging to study marine megafauna, yet are rarely deployed within freshwater ecosystems despite parallel research needs. Adult lake sturgeon were fitted with satellite tags containing integrated accelerometers near spawning grounds in the Niagara River between Canada and the United States. We used the time-series of acceleration in recovered tags to test the hypothesis that lake sturgeon exhibit diel activity cycles in situ. We defined activity as acceleration greater than two standard deviations from a running average. We applied this classification to partial records obtained from satellite transmission, an approach that can render incomplete datasets a useable product for analysis. Lake sturgeon were most active nocturnally with a significant mean at 22:32 h. Generalized linear mixed-effect models showed temperature and time of day to be significant predictors of activity. Temporal cycles of fish activity should be understood and could be exploited to reduce human-fish conflict in the increasingly altered waterways of the globe.     

人工鱼群算法在湖泊富营养化综合评价中的应用

提出了一种对多项指标都能普遍适用的湖泊水质富营养化评价的逻辑斯谛模型,将人工鱼群算法应用于逻辑斯谛曲线模型中的参数优化,并用优化后的逻辑斯谛曲线模型对湖泊富营养进行综合评价。对我国5个湖泊富营养化实测数据进行评价实例研究,并与其他多种评价方法进行比较,结果表明该模型具有实用性和可行性。     

白马湖退圩还湖方案及效果浅析

根据白马湖圈圩现状和退圩还湖规划标准、目标、建设规模,提出白马湖退圩还湖4个方案,通过各方案水位—库容曲线、入湖流量过程设计、出湖流量过程计算,并进行调洪演算,分析不同方案的防洪滞涝效果,提出了淮安市白马湖近期退圩还湖建议实施方案。     

太湖蓝藻水华和湖泛应急防控能力提升对策研究

本文通过回顾江苏省水利部门2007年以来太湖蓝藻水华及湖泛防控工作进展,总结了太湖蓝藻预警、打捞处置、藻泥利用以及规范化管理等方面的经验做法。同时,分析了现阶段太湖安全度夏面临的蓝藻生物量居高不下、应急防控成本增加、监管能力不足等难点问题,提出了加快骨干引排工程建设、提升蓝藻水华防控能力、加快构建信息化监管平台,以及健全应急防控标准体系等工作建议,为提升太湖应急防控工作水平提供技术支撑。     

引水济湖工程措施的生态环境影响评价方法

在湖泊引水方案和二维环境流体动力学模型影响预测计算结果的基础上,提出引水后湖泊环境生态影响预测评价方法:①从湖泊水景的自然度、自净(健康)度、景观度、亲水度、连通度5个方面,构造了引江济湖工程对湖泊生态-环境-景观综合影响指数评价法;②从水环境质量、生物多样性、防洪排涝、景观生态结构等方面应用质量指标法进行工程对湖泊健康综合影响评价。实例应用表明,两种评价方法可以对湖泊引水影响效果进行科学评价,结论也比较一致,为正确实施引水济湖方案提供了科学评估方法和依据。