Lake Sturgeon Eggs Research Articles

Aquatic insects differentially affect lake sturgeon larval phenotypes and egg surface microbial communities.

Documentation of how interactions among members of different stream communities [e.g., microbial communities and aquatic insect taxa exhibiting different feeding strategies (FS)] collectively influence the growth, survival, and recruitment of stream fishes is limited. Considerable spatial overlap exists between early life stages of stream fishes, including species of conservation concern like lake sturgeon (Acipenser fulvescens), and aquatic insects and microbial taxa that abundantly occupy substrates on which spawning occurs. Habitat overlap suggests that species interactions across trophic levels may be common, but outcomes of these interactions are poorly understood. We conducted an experiment where lake sturgeon eggs were fertilized and incubated in the presence of individuals from one of four aquatic insect FS taxa including predators, facultative and obligate-scrapers, collector-filterers/facultative predators, and a control (no insects). We quantified and compared the effects of different insect taxa on the taxonomic composition and relative abundance of egg surface bacterial and lower eukaryotic communities, egg size, incubation time to hatch, free embryo body size (total length) at hatch, yolk-sac area, (a measure of resource utilization), and percent survival to hatch. Mean egg size varied significantly among insect treatments. Eggs exposed to predators had a lower mean percent survival to hatch. Eggs exposed to predators had significantly shorter incubation periods. At hatch, free embryos exposed to predators had significantly smaller yolk sacs and total length. Multivariate analyses revealed that egg bacterial and lower eukaryotic surface community composition varied significantly among insect treatments and between time periods (1 vs 4 days post-fertilization). Quantitative PCR documented significant differences in bacterial 16S copy number, and thus abundance on egg surfaces varied across insect treatments. Results indicate that lethal and non-lethal effects associated with interactions between lake sturgeon eggs and free embryos and aquatic insects, particularly predators, contributed to lake sturgeon trait variability that may affect population levels of recruitment.

Exposure of Juvenile Lake Sturgeon to Contaminants of Emerging Concern (CECs), Including Polybrominated Diphenyl Ethers (PBDEs): Location Differences and Effects on Thyroid Hormones

AbstractContaminants of emerging concern (CECs) are ubiquitous throughout aquatic environments. Previous research has shown that CECs can have detrimental effects on fish biology, potentially leading to population impacts. Specifically, polybrominated diphenyl ethers (PBDEs), a class of CECs, have been shown to alter thyroid hormones in fish, which can impact development, endocrine system functioning, and possibly imprinting. These impacts can lead to reproductive effects and population declines, which have serious implications for species of conservation priority, such as the Lake Sturgeon Acipenser fulvescens. To assess the effects of CECs and PBDEs, Lake Sturgeon were evaluated at rearing facilities within the Great Lakes basin during 2017–2018 to determine (1) whether exposure to CECs and PBDEs differs between facility locations and (2) whether changes in whole‐body PBDE concentrations correlate with changes in thyroid hormones (triiodothyronine [T3] and thyroxine [T4]), which could indicate impacts to imprinting. Exposure to CECs and PBDEs differed among sites. The CECs that were detected in water across all sites included atrazine, hexachlorobenzene, N,N‐diethyl‐meta‐toluamide (DEET), desethylatrazine, erythromycin, and metformin, with the highest concentrations (except for DEET) measured at the Maumee River (Ohio) streamside rearing facility. We detected PBDEs in every sample of water, food, and Lake Sturgeon eggs and whole bodies, and there were no differences in lipid‐normalized total PBDE concentrations in whole bodies across sites. Concentrations of total PBDE and the PBDE congeners 47, 99, 100, 153, 154, and 209 in fish tissues did not correlate with serum T3 and T4 levels, indicating that observed concentrations were unlikely to negatively impact Lake Sturgeon rearing for the biological endpoints assessed. Overall, this study exemplifies a cautionary tale since CECs and PBDEs were identified throughout Lake Sturgeon habitat and in hatchery food sources. Fisheries managers should be aware of the potential for CEC and PBDE impacts even though current observed levels do not seem to be impacting Lake Sturgeon rearing success.

Egg lipid and thiamine vary between early and late spawning lake sturgeon

Nutritional deficiency associated with reduced thiamine (vitamin B1) and reduced natural reproduction of salmonid species in the Great Lake Region is well established. The negative relationship between egg thiamine and lipid concentration to post-hatch larval growth and survival in teleost species, coupled with the limited research of egg thiamine in Acipenseriform species of conservation concern, including lake sturgeon, indicates that study of thiamine concentrations lake sturgeon eggs is warranted. Eggs were collected from females (N = 12) during the early and late portion of the spawning run in 2007 in a wild population from Black Lake, MI. Concentrations of thiamine, lipid and fatty acid concentration were measured along with female biological information (body size and egg size) and characteristics of larvae at hatch. Significant differences in egg thiamine concentrations were observed between early- and late-spawning females (mean ± SD: 2.36 nmol·g−1 ± 1.09 vs. 0.73 ± 0.25 nmol·g−1, W = 0.05, p < .01). No significant relationships were observed between female body size or egg size and egg lipid or thiamine concentration. Differences in lipid and thiamine concentrations were not predictive of larval body size or yolk sac volume at hatch. Total and phosphorylated thiamine were correlated with n-3 polyunsaturated fatty acids, suggesting that dietary items were likely partially responsible for provisioning of essential compounds. Given the negative effects of low egg thiamine concentration on larval survival in other fish species globally, results indicate that further research in areas of nutrient acquisition and thiamine effects on larval survival, natural recruitment, and hatchery feeding strategies is warranted for lake sturgeon.

Effects of Water Filtration and Temperature on Microbial Colonization and Survival of Lake Sturgeon Eggs

AbstractPhysical and biotic factors that affect development and survival during the embryonic period of fish are major concerns in aquaculture, particularly when individuals are produced using natural surface water sources. We quantified the effects of bacterial community taxonomic composition and abundance, water filtration treatment, and incubation temperature on the development and survival of embryos from Lake Sturgeon Acipenser fulvescens, a threatened Great Lakes fish species. Eggs were fertilized and incubated using a two‐by‐two treatment design by manipulating water treatments (treated [filtered and UV treated] and untreated stream water) and temperature (12°C and 18°C) during incubation. Egg samples from five full‐sibling families were exposed to each rearing treatment. At different stages during development, eggs were analyzed for egg surface microbial community composition and abundance using terminal restriction fragment length polymorphism methods based on the 16S rRNA gene and quantitative PCR, respectively. Sanger sequencing identified egg‐associated microbial taxa. Microbial community composition derived from terminal restriction fragment length polymorphism was visualized using principal component analysis. Permutational multivariate analysis of variance revealed that the composition of microbial communities that developed on egg surfaces varied as a function of water filtration and temperature. Quantitative PCR analysis revealed that significantly higher microbial abundance was present on surfaces of eggs reared in untreated stream water than on those reared in treated stream water. Temperature did not affect egg surface microbial abundance. Significantly higher egg mortality was documented for eggs reared in unfiltered stream water (mean ± SD = 77.4 ± 17.6%) than for eggs reared in treated stream water (50.3 ± 14.7%). Temperature during incubation did not affect levels of egg mortality. Sequence analysis revealed that certain microbial taxa were associated with eggs characterized by higher survival, including Acidovorax spp. and Massilia spp., suggesting that they may be candidates for natural probiotics. Filtration and UV treatment of surface water was an effective method for modification of egg microbial community composition and quantity and significantly reduced egg mortality.

Observations regarding Lake Sturgeon spawning below a hydroelectric generating station on a large river based on egg deposition studies

AbstractSpawning behaviour of the Lake Sturgeon (Acipenser fulvescens) in large rivers is poorly understood, complicating the approach to fish‐friendly hydroelectric design and mitigation. In 2006, dam safety concerns prompted the need to modernize the spillway infrastructure of the 100‐year old Pointe du Bois Generating Station on the Winnipeg River, Manitoba. The associated regulatory process provided an opportunity to study Lake Sturgeon spawning in a location characterized by water depths &gt;5 m, high velocities, and hydraulic instability. Over six spawning periods (2007–2012), a wide range of flow conditions occurred, and spawning was documented using egg mats in both the powerhouse tailrace and downstream of the spillway rapids. Herein, we consider “….the preferential utilization by sturgeon of certain ranges of the physical variables studied, but within habitats considered favourable for the reproduction of the species” conclusion forwarded by La Haye et al. as our working hypothesis. Overall, 27,362 of 30,085 (90.1%) Lake Sturgeon eggs were captured during the primary spawning intervals, defined based on 6‐day annual periods encompassing the date of peak deposition. Of the 2,200 mats retrieved, 74.4% captured 0 eggs, 12.0% captured 1–5 eggs, 5.2% captured 6–25 eggs, 6.1% captured 26–99 eggs, and just 2.2% captured ≥100 eggs (high‐yield). Data were examined in relation to status‐quo habitat variables (depth, velocity, and substrate), as well as two additional variables hypothesized to have predictive power: distance from physical and/or energetic barriers and hydraulic complexity. Distance‐based analyses revealed upstream to downstream redistribution of eggs via flow. Spawning (as inferred based on high‐yield mats) was spatially discrete during each spawning period as opposed to well‐distributed among habitats broadly considered to be suitable for the species. We suggest that the current‐edges located proximal to physical and/or energetic barriers (i.e., at the upstream extent of usable habitat) drive Lake Sturgeon spawning site selection in large rivers, and advise caution prior to making fine‐scale inferences when only small quantities of Lake Sturgeon eggs are captured.

Lake sturgeon (Acipenser fulvescens) spawn in the St. Marys River Rapids, Michigan

The St. Marys River connects Lake Superior to Lake Huron, comprising the international border between Michigan, United States, and Ontario, Canada. This Great Lakes connecting channel naturally encompasses various habitats including lakes, wetlands, islands, tributaries, side channels, and main channels. The St. Marys River Rapids are shallow rock areas with high flow velocities (>1 m/s) in the upper river adjacent to the navigation locks and electric power generating stations, while the Little Rapids are shallow, recently restored rocky areas with lower velocities located about 7 km downstream. The St. Marys River Rapids provide important spawning habitat for several native and introduced fishes, but spawning by lake sturgeon (Acipenser fulvescens) was not previously documented. We sampled for lake sturgeon eggs and larvae in both locations during June and July 2018–2019 using weekly benthic egg mat lifts and overnight D-frame larval fish drift nets. Viable lake sturgeon eggs (11 in 2018, 45 in 2019) were collected in the tailrace of a hydroelectric power facility adjacent to the St. Marys River Rapids. Larval lake sturgeon (21 in 2018, 1 in 2019) were collected in the same area as the eggs. Neither lake sturgeon eggs nor larvae were collected at Little Rapids in either year. Our results are the first documentation of successful lake sturgeon spawning and larval drift in the upper St. Marys River. While our observations showed spawning in a human-made tailrace area, the fate of larvae produced here is unknown and warrants further research.

High-stress rearing temperature in Acipenser fulvescens affects physiology, behaviour and predation rates

Early life stress can lead to long-term behavioural and physiological phenotypic alterations that impact fitness. Understanding effects of environmental stressors on wildlife is important to predict individual and population-level responses to stressors associated with climate change. Lake sturgeon, Acipenser fulvescens, are a regionally threatened fish species that experience high predation rates during larval stages. To investigate effects of a high temperature stressor, we exposed lake sturgeon eggs from four families to 10 °C (low-stress) or 18 °C (high-stress) rearing temperatures. At egg, free embryo and larval stages, we quantified stress levels for individuals from each treatment using whole-body cortisol analysis at baseline and after an acute stressor. At the larval stage, we videorecorded behaviour trials to quantify swimming activity, and we conducted predation trials to quantify survival outcomes for individuals from high-stress and low-stress temperature treatments. Free embryos reared at 18 °C had a significantly smaller cortisol response after exposure to an acute stressor, indicating that chronic high temperature stress may reduce stress reactivity in lake sturgeon. In addition, larvae reared at 18 °C had significantly higher activity levels during behaviour trials and significantly higher survival rates when exposed to crayfish predation, indicating that behavioural alterations induced by early life stress may be adaptive in high-stress contexts such as predation. These findings illustrate the need to experimentally evaluate fitness effects of stressors within ecologically relevant contexts in order to predict population- and community-level outcomes of climate change.

Discovery of an Undocumented Lake Sturgeon Spawning Site in the Headwaters of the Niagara River

Abstract Information about spawning fish is important to stock-assessment data needs (i.e., recruitment and fecundity) and management (i.e., habitat connectivity and protection). In Lake Erie, information about Lake Sturgeon Acipenser fulvescens early-life history is available for the Detroit River and Lake St. Clair system in the western basin, but fisheries biologists know comparatively little about Lake Sturgeon in the eastern basin. Although researchers have summarized historical spawning areas, no known natural Lake Sturgeon spawning site is described in Lake Erie proper. Researchers documented a remnant population of reproductively mature Lake Sturgeon near the headwaters of the Niagara River in eastern Lake Erie in 2011. Researchers hypothesized that a spawning site was likely in the immediate vicinity of the Niagara River headwaters near Buffalo Harbor, New York; however, its exact location was unknown. We attempted to locate spawning sites near the confluence of the Niagara River using egg traps at three potential spawning sites. We identified Lake Sturgeon eggs at one of these sites using morphological and genetic techniques. Lake Sturgeon eggs collected on one sampling trip began to emerge when placed in preservative, confirming that eggs deposited at this site are fertilized and viable, and that the area supports viable embryos. This discovery fills data gaps in the early-life history for this population, which has domestic and international management implications with respect to proposed recovery targets, stock assessment models, habitat remediation efforts, and status determinations of a protected species in a geographic region designated as an Area of Concern by the International Joint Commission.

Effects of crayfish density, body size and substrate on consumption of lake sturgeon (Acipenser fulvescens Rafinesque, 1817) eggs by invasive rusty crayfish [(Orconectes rusticus (Girard, 1852)

The density and size of benthic predators such as crayfish and the physical characteristics of aquatic habitats including benthic substrate size have been hypothesized to significantly affect levels of lake sturgeon (Acipenser fulvescens) egg consumption. The invasive rusty crayfish (Orconectes rusticus) was used to quantify consumption and apportion variation in egg loss in an experimental setting. Experiments consisted of large flow-through rectangular tanks (0.8 m wide, 2.96 m2 total bottom surface area) receiving river water to mimic natural diel temperature regimes. Four crayfish densities were tested (5, 10, 15, 30 individuals or 1.7, 3.4, 5.1, 10.1 individuals/m2) that span the range of densities observed in natural settings. Crayfish were allowed to freely move among three substrates commonly found at spawning locations where lake sturgeon eggs are deposited (cobble, gravel and sand). After an acclimation period (15 min), 200 lake sturgeon eggs were randomly scattered over each substrate category (600 eggs per tank). Mean (± SE) egg consumption over 48 hr was 80 ± 3% (range 19–100% across 16 replicate trials). Egg consumption increased significantly as a function of increasing crayfish density. The effect of substrate size, however, depended significantly on crayfish density (substrate size × predator density interaction). Egg consumption significantly increased as substrate size decreased (e.g. from gravel to sand), at both high and low crayfish densities. Egg consumption also increased with increasing mean crayfish body size. Our results revealed that levels of lake sturgeon egg consumption by rusty crayfish are high in some settings. Further work is needed to determine if egg consumption in natural river settings is similarly high and whether egg consumption by crayfish and other egg predators could negatively affect population levels of recruitment.

Lake Sturgeon, Lake Whitefish, and Walleye Egg Deposition Patterns with Response to Fish Spawning Substrate Restoration in the St. Clair–Detroit River System

AbstractEgg deposition and use of restored spawning substrates by lithophilic fishes (e.g., Lake SturgeonAcipenser fulvescens, Lake WhitefishCoregonus clupeaformis, and WalleyeSander vitreus) were assessed throughout the St. Clair–Detroit River system from 2005 to 2016. Bayesian models were used to quantify egg abundance and presence/absence relative to site‐specific variables (e.g., depth, velocity, and artificial spawning reef presence) and temperature to evaluate fish use of restored artificial spawning reefs and assess patterns in egg deposition. Lake Whitefish and Walleye egg abundance, probability of detection, and probability of occupancy were assessed with detection‐adjusted methods; Lake Sturgeon egg abundance and probability of occurrence were assessed using delta‐lognormal methods. The models indicated that the probability of Walleye eggs occupying a site increased with water velocity and that the rate of increase decreased with depth, whereas Lake Whitefish egg occupancy was not correlated with any of the attributes considered. Egg deposition by Lake Whitefish and Walleyes was greater at sites with high water velocities and was lower over artificial spawning reefs. Lake Sturgeon eggs were collected least frequently but were more likely to be collected over artificial spawning reefs and in greater abundances than elsewhere. Detection‐adjusted egg abundances were not greater over artificial spawning reefs, indicating that these projects may not directly benefit spawning Walleyes and Lake Whitefish. However, 98% of the Lake Sturgeon eggs observed were collected over artificial spawning reefs, supporting the hypothesis that the reefs provided spawning sites for Lake Sturgeon and could mitigate historic losses of Lake Sturgeon spawning habitat.

Determination of cortisol in lake sturgeon (Acipenser fulvescens) eggs by liquid chromatography tandem mass spectrometry.

Quantifying cortisol concentrations in fish eggs is important to understand the effects of environmental conditions on maternal physiological condition and on egg provisioning and quality. Data are particularly relevant to studies of the ecology of threatened species such as lake sturgeon (Aciperser fulvescens) as well as assessments of larval physical and behavioral phenotypes, fish health and caviar quality in sturgeon aquaculture. This study focuses on development of bioanalytical methods for high sensitivity and robust determination of cortisol in sturgeon eggs. Sample preparation was optimized after investigating protein precipitation and liquid-liquid extraction techniques. Ethyl acetate was found to be the most efficient solvent (recovery parameter) and also provided the best sample clean up (matrix effect parameter). The method was determined to be linear for cortisol concentrations between 0.025 and 100ng/mL. The limits of detection and quantification were 0.025 and 0.1ng/mL respectively. Intra- and inter-day performances of the method were validated at three concentrations (0.25; 10 and 100ng/mL). The method was applied to field-collected samples for the determination of endogenous cortisol in lake sturgeon eggs. Cortisol was detected in all egg samples and statistical analysis showed significant differences between fertilized and non-fertilized eggs.

Efficacy of Iodine for Disinfection of Lake Sturgeon Eggs from the St. Lawrence River, New York

AbstractOptimal fish husbandry to reduce the risk of disease is particularly important when using wild fish as the source for gametes. The propagation and reestablishment of Lake Sturgeon Acipenser fulvescens in New York waters to become a viable self‐sustaining population is considered a high priority by managers. While standard hatchery egg disinfection practices have been used to prevent the transmission of diseases, data on the bacterial loads present on egg surfaces following iodine disinfection is lacking. Our study investigated the bacteria present on the outer surface of Lake Sturgeon eggs and the effectiveness of an iodine disinfection treatment in eliminating bacteria that could pose a threat to egg survival and cause hatchery disease outbreaks. During the springs of 2011–2013, 12 to 41 different species of bacteria were recovered from the outer egg surfaces prior to an iodine treatment; Aeromonas, Pseudomonas, Shewanella, and Chryseobacterium were the most common genera identified. Cohort eggs treated using the standard protocol of a single treatment of 50 mg/L iodine for 30 min resulted in an average of 57.8% reduction in bacterial CFU/g. While this is a significant reduction, bacteria were not completely eliminated and hatchery managers should be aware that pathogens could remain on Lake Sturgeon eggs following the standard iodine disinfection treatment.

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.

Microbial Community Assembly and Succession on Lake Sturgeon Egg Surfaces as a Function of Simulated Spawning Stream Flow Rate

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.

Experimental Assessment of the Magnitude and Sources of Lake Sturgeon Egg Mortality

AbstractMortality 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 of mortality (84%) than the combined effect of predation and scour or de‐adhesion (16%). We also documented a significant treatment by time (day of incubation) interaction, indicating that although cumulative rates of mortality may not vary significantly among spawning sites, the relative contributions of different sources of mortality can vary greatly at different times during egg incubation.

Lake sturgeon response to a spawning reef constructed in the Detroit river

Summary Prior to the First World War, the bi-national Detroit River provided vast areas of functional fish spawning and nursery habitat. However, ongoing conflicting human uses of these waters for activities such as waste disposal, water withdrawals, shoreline development, shipping, recreation, and fishing have altered many of the chemical, physical, and biological processes of the Detroit River. Of particular interest and concern to resource managers and stakeholders is the significant loss and impairment of fish spawning and nursery habitat that led to the decline in abundance of most fish species using this ecosystem. Lake sturgeon (Acipenser fulvescens) populations for example, were nearly extirpated by the middle of the 20th century, leaving only a small fraction of their former population. Fisheries managers recognized that the loss of suitable fish spawning habitat is a limiting factor in lake sturgeon population rehabilitation in the Detroit River. In efforts to remediate this beneficial water use impairment, a reef consisting of a mixture of natural rock and limestone was constructed at the upstream end of Fighting Island in 2008. This paper focuses on the response by lake sturgeon to the different replicates of suitable natural materials used to construct the fish spawning habitat at Fighting Island in the Detroit River. Pre-construction fisheries assessment during 2006–2008 showed that along with the presence of adult lake sturgeon, spawning conditions were favorable. However, no eggs were found in assessments conducted prior to reef construction. The 3300 m2 Fighting Island reef was placed at the upstream end of the island in October of 2008. The construction design included 12 spawning beds of three replicates each consisting of either round rock, small or large (shot-rock) diameter limestone or a mixture thereof. An observed response by spawning lake sturgeon occurred the following year when spawning-ready adults (ripe), viable eggs, and larvae were collected during May and June 2009. Additional eggs and spawning-ready adults were found in 2010 (no larval sampling occurred in 2010) as well as collection of three age-0 juvenile lake sturgeon in bottom trawls fished downstream of the reef during July 2010. Spawning lake sturgeon showed no repeatable preference for any of the four particular substrate types but showed a high degree of preference for the island side of the channel, where faster water current velocities occurred. In 2009, overall lake sturgeon egg densities across all replicates averaged 102 m−2 and seven larvae were found in night drift-net samples. In 2010, average lake sturgeon egg density was 12 m−2 and three age-0 lake sturgeon averaging 120 mm TL were collected in bottom trawls in deepwater (∼8 m depth) downstream from the constructed reef. These results demonstrated successful reproduction by lake sturgeon on a man-made reef and suggested that additions and improvements to fish spawning habitat could enhance reproduction and early life history survival of lake sturgeon in the Detroit River.

Predation on Early Life Stages of Lake Sturgeon in the Peshtigo River, Wisconsin

AbstractMortality of early life stages can limit recruitment of fishes, and understanding the impacts of various sources of mortality has long been a goal of fisheries management. The impacts of predation on lake sturgeon Acipenser fulvescens are not well understood. The objective of this study was to identify and quantify sources of predation that affect lake sturgeon eggs, larvae, and age‐0 juveniles in the Peshtigo River, Wisconsin, during 2006 and 2007. Egg bags were used to assess the rate of lake sturgeon egg consumption by crayfishes Orconectes spp. Potential piscine predators on eggs, larvae, or age‐0 juveniles were captured using fyke nets, gill nets, hoop nets, and electrofishing for analysis of stomach contents. Crayfish consumed lake sturgeon eggs at an average rate of 9.4 eggs/d, and the population of crayfish within the lake sturgeon spawning habitat consumed an estimated 300,000 eggs during the incubation period. Numerous fish species were observed consuming lake sturgeon eggs, and piscine predators likely consumed most eggs that settled on the surface of the substrate. Within 862 predator stomachs, only a single lake sturgeon larva was observed, and there was no evidence of predation on age‐0 juveniles. These results suggest that predation could limit recruitment at the egg stage, but it does not appear to be limiting to the larval and age‐0 juvenile life stages in the Peshtigo River.

Early Life Stage Mortality Rates of Lake Sturgeon in the Peshtigo River, Wisconsin

AbstractA thorough understanding of the early life history of lake sturgeon Acipenser fulvescens is critical for rehabilitation of this species. Recruitment of lake sturgeon is known to be variable, but the extent of that variation and mortality rates experienced by early life stages are unclear. The objective of this study was to quantify early life stage mortality and explore the variability in year‐class strength by estimating total egg deposition and abundance of larval and age‐0 juvenile lake sturgeon from the 2006 and 2007 year‐classes in the Peshtigo River, Wisconsin. Egg mats, drift nets, and visual surveys were used to collect lake sturgeon eggs, larvae, and age‐0 juveniles, respectively. Total egg deposition, larval abundance, and age‐0 juvenile abundance were higher in 2007 than in 2006. The magnitude of difference ranged from 2 times for eggs to 11 times for age‐0 juveniles. The rate of mortality from the larval stage to the age‐0 juvenile stage was higher in 2006 (98.26%) than in 2007 (90.46%); overall mortality from the egg stage to the age‐0 juvenile stage was also higher in 2006 (99.98%) than 2007 (99.93%). These results suggest that mortality rates for these life stages of lake sturgeon are high, and large variation in early life stage abundance may be common. Management strategies to reduce these mortality rates may increase recruitment and aid population recovery.

Lake Sturgeon Spawning Habitat in the Big Manistee River, Michigan

AbstractSpawning sites of lake sturgeon Acipenser fulvescens were verified using egg collection mats in the Big Manistee River in northwestern lower Michigan. Photographs taken by a fixed‐position underwater video camera were used to characterize the substrate at egg mat locations. A total of 3,913 lake sturgeon eggs were captured at two discrete spawning locations in 2003 and 2004. Spawning locations consisted of 34–44% cobble and 0.04–8% sand, and nonspawning locations consisted of 2–43% cobble and 0.16–7% sand. Shannon diversity indices describing substrate heterogeneity at spawning locations were statistically higher than those for nonspawning locations in 2003 (P = 0.002). Four spawning events (one in 2003 and three in 2004) were documented at water temperatures ranging from 11.1°C to 14.8°C and egg incubation periods ranging from 6 to 10 d. Depth at spawning sites was 1.5–3.0 m, average water velocity was 0.34–1.32 m/s, and near‐substrate water velocity was 0.08–1.26 m/s. The topography of the Big Manistee River channel appears to have been altered by manipulated river flows, resulting in the development of barchans (ridges or shelves along the river bottom) in the region utilized for spawning. This study is the first to document lake sturgeon spawning success in the Big Manistee River and identify the specific characteristics of spawning bed material used as well as the presence of barchans that may produce eddies or turbulent irregular flows that affect egg dispersal and survival.

Fecundity of Lake Sturgeon (Acipenser fulvescens, Rafinesque) in Lake Winnebago, Wisconsin, USA

Summary Sturgeon species are known for their relatively high fecundity, with some reported to carry as many as 7.7-million eggs. However, the fecundity of lake sturgeon (Acipenser fulvescesn Rafinesque) has not been thoroughly studied, with limited information available primarily in gray literature and agency reports. Our objectives were to quantify (1) the fecundity and gonadosomatic index (GSI) of female lake sturgeon in a winter F4 stage of development; 2) the average size and weight of F4 lake sturgeon eggs; and 3) relationships between lake sturgeon fecundity and fish weight, length, and age. Total length, weight, age, gonad weight, fecundity, egg diameter, and egg weight were sampled from 14 female lake sturgeon in an F4 stage of egg development in February 2005 from the Lake Winnebago System in Wisconsin. Mean fecundity was 383,529 eggs and the mean GSI was 22.9. Egg diameter averaged 2.74 mm and egg weight averaged 17.34 mg. Weight was the best predictor of fecundity (r 2 = 0.66). Fecundity data for lake sturgeon larger than 35 kg are needed to allow better estimation of fecundity for larger fish.