Pallid Sturgeon Research Articles

Population size of pallid sturgeon, Scaphirhynchus albus (Forbes & Richardson, 1905), in the lower Missouri River near Kansas City, Missouri, USA

Summary The objectives of this study were to investigate the population size of hatchery-reared and wild pallid sturgeon, Scaphirhynchus albus (Forbes & Richardson, 1905), in a 43.3 river kilometer (rkm) reach of the Missouri River downstream of Kansas City, Missouri, USA and compare these with previous published estimates. This reach has been shown to represent the abundance and distribution of the pallid sturgeon population throughout the lower Missouri River, and was therefore chosen for this study in order to monitor progress towards recovering this federally endangered species. The robust-design approach was used within the Program MARK using mark-recapture data of fish sampled from 2011 to 2013. The annual population estimates of pallid sturgeon varied from 6.1 to 11.1 fish/rkm, of which known hatchery-origin pallid sturgeon (5.5 to 10.2 fish/rkm) were much more abundant than those of wild origin (0.6 to 0.9 fish/rkm). These population estimates are drastically fewer than those published for another reach of the lower Missouri River and represent far less advancement (12–18%) towards meeting the five wild adult fish/rkm criteria for considering reclassification of pallid sturgeon.

In situ and laboratory toxicity of coalbed natural gas produced waters with elevated sodium bicarbonate.

Some tributaries in the Powder River Structural Basin, USA, were historically ephemeral, but now contain water year round as a result of discharge of coalbed natural gas (CBNG)-produced waters. This presented the opportunity to study field sites with 100% effluent water with elevated concentrations of sodium bicarbonate. In situ experiments, static renewal experiments performed simultaneously with in situ experiments, and static renewal experiments performed with site water in the laboratory demonstrated that CBNG-produced water reduces survival of fathead minnow (Pimephales promelas) and pallid sturgeon (Scaphirhynchus albus). Age affected survival of fathead minnow, where fish 2 d posthatch (dph) were more sensitive than 6 dph fish, but pallid sturgeon survival was adversely affected at both 4 and 6 dph. This may have implications for acute assays that allow for the use of fish up to 14 dph. The survival of early lifestage fish is reduced significantly in the field when concentrations of NaHCO(3) rise to more than 1500 mg/L (also expressed as >1245 mg HCO(3) (-) /L). Treatment with the Higgin's Loop technology and dilution of untreated water increased survival in the laboratory. The mixing zones of the 3 outfalls studied ranged from approximately 800 m to 1200 m below the confluence. These experiments addressed the acute toxicity of effluent waters but did not address issues related to the volumes of water that may be added to the watershed.

Seasonal diet composition of juvenile and adult pallid sturgeon,Scaphirhynchus albus(Forbes & Richardson, 1905), in the channelized lower Missouri River

Summary Although habitat alterations and reproductive success are the main contributors to declines of the pallid sturgeon, Scaphirhynchus albus (Forbes & Richardson, 1905) listed in 1990 as federally endangered, disrupted trophic links within diets of pallid sturgeon populations have been hypothesized as partial contributors. The objective of this study was to evaluate pallid sturgeon food habits within a 500 km reach of the lower channelized Missouri River using non-lethal pulsed gastric lavage. Trotlines, gill nets, trammel nets, and benthic otter trawls were used to collect 284 pallid sturgeon, which ranged in fork length from 265 to 1047 mm. Stomach contents of pallid sturgeon included fish (Cyprinidae and Ictaluridae), aquatic insects, copepods, leeches, and mussels. Cyprinids were the most abundant prey item; ictalurids were also of high abundance. Otter trawl catch rates of ictalurids and cyprinids were not spatially correlated to the respective abundances in pallid sturgeon diets; however, the ratio of the average catch rate to the average number of fish per pallid sturgeon indicated preference for cyprinids (1.5 : 1), particularly Macrhybopsis species, relative to ictalurids (7 : 1). Our results support the need for management of native cyprinids, especially Macrhybopsis species, which have been in decline within the entire range of the pallid sturgeon. However, pallid sturgeon are also able to consume ictalurids, a species which has remained in high abundance in the lower Missouri River.

Susceptibility of fish and turtles to three ranaviruses isolated from different ectothermic vertebrate classes.

Ranaviruses have been associated with mortality of lower vertebrates around the world. Frog virus 3 (FV3)-like ranaviruses have been isolated from different ectothermic vertebrate classes; however, few studies have demonstrated whether this pathogen can be transmitted among classes. Using FV3-like ranaviruses isolated from the American bullfrog Lithobates catesbeianus, eastern box turtle Terrapene carolina carolina, and Pallid Sturgeon Scaphirhynchus albus, we tested for the occurrence of interclass transmission (i.e., infection) and host susceptibility (i.e., percent mortality) for five juvenile fish and three juvenile turtle species exposed to each of these isolates. Exposure was administered via water bath (10(3) PFU/mL) for 3 d and survival was monitored for 28 d. Florida softshell turtles Apalone ferox experienced no mortality, but 10% and 20% of individuals became infected by the turtle and fish isolate, respectively. Similarly, 5% of Mississippi map turtles Graptemys pseudogeographica kohni were subclinically infected with the turtle isolate at the end of the experiment. Channel Catfish Ictalurus punctatus experienced 5% mortality when exposed to the turtle isolate, while Western Mosquitofish Gambusia affinis experienced 10% mortality when exposed to the turtle and amphibian isolates and 5% mortality when exposed to the fish isolate. Our results demonstrated that interclass transmission of FV3-like ranaviruses is possible. Although substantial mortality did not occur in our experiments, the occurrence of low mortality and subclinical infections suggest that fish and aquatic turtles may function as reservoirs for FV3-like ranaviruses. Additionally, our study is the first to report transmission of FV3-like ranaviruses between fish and chelonians.

Influence of Channel Morphology and Flow Regime on Larval Drift of Pallid Sturgeon in the Lower Missouri River

AbstractThe transition from drifting free embryo to exogenously feeding larvae has been identified as a potential life‐stage bottleneck for the endangered Missouri River pallid sturgeon. Previous studies have indicated that river regulation and fragmentation may contribute to the mortality of larval pallid sturgeon by reducing the extent of free‐flowing river available to free embryos to complete ontogenetic development. Calculations of total drift distance based on mean velocity, however, do not address the potential for complex channels and flow patterns to increase retention or longitudinal dispersion of free embryos. We use a one‐dimensional advection–dispersion model to estimate total drift distance and employ the longitudinal dispersion coefficient as a metric to quantify the tendency towards dispersion or retention of passively drifting larvae. We describe the effects of different styles of channel morphology on larval dispersion and consider the implications of flow regime modifications on retention of free embryos within the Lower Missouri River. The results illustrate the complex interactions of local morphology, engineered structures, and hydraulics that determine patterns of dispersion in riverine environments and inform how changes to channel morphology and flow regime may alter dispersion of drifting organisms. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Using mark–recapture information to validate and assess age and growth of long-lived fish species

Long-lived species from marine and freshwater environments have experienced declines linked to anthropogenic effects such as overexploitation, dam construction, and habitat modification. An understanding of the age structure and the associated dynamics determined from these data for long-lived species is critical for both perseverance of at-risk species and maintenance of exploited species. We used pallid sturgeon (Scaphirhynchus albus) to evaluate the efficacy of mark–recapture data from known-age, hatchery-reared fish (ages 1 to 7) to corroborate age and growth estimates obtained from sectioned pectoral fin rays. Accuracy of age estimates from known-age fish was 13%, whereas 72% of estimates were within 2 years of the true age. Annual growth was significantly different between estimated growth (back-calculated) and actual observations of tagged pallid sturgeon. Age for pallid sturgeon of any given size was estimated with parameters derived from mark–recapture data, and the predicted length-at-age relation was similar to observations from known individuals. In instances where age determination for all ages of interest cannot be verified, mark–recapture appears to be a viable solution for examining growth and has shown promise as a tool for estimating ages in long-lived species with calcified structures that are difficult to read.

Stress Responses in Pallid Sturgeon Following Three Simulated Hatchery Stressors

AbstractBecause sturgeon populations are in critical decline, many species are artificially propagated in hatcheries with the goal of increasing wild stocks. Capture, transport, handling, confinement, and environmental fluctuations are just a few of the possible stressors Pallid Sturgeon Scaphirhynchus albus can be exposed to in conservation hatcheries. The objectives of the present study were to elucidate the effects of acute exposure to high ammonia concentrations, low dissolved oxygen (DO) concentrations, and crowding on stress responses in Pallid Sturgeon, quantified by changes in plasma cortisol and glucose. Exposure to un‐ionized ammonia‐nitrogen concentrations of 0.6 mg/L for 24 h resulted in no significant (P > 0.05) change in plasma cortisol concentrations, suggesting these fish do not perceive the buildup of toxins. Exposure to 2 mg/L DO over a 0.5‐h period resulted in a significant (P < 0.05) increase in plasma cortisol concentrations during the low DO challenge, with levels decreasing (P > 0.05) within 30 min of recovery and returning to prestress levels within 2.5 h of recovery. Plasma cortisol concentrations increased (P < 0.05) within 0.25 h of crowding and remained elevated after 0.5 h of crowding. Removal of the crowding stressor did not result (P > 0.05) in decreased circulating cortisol within 30 min. Regardless of the stressor, Pallid Sturgeon plasma glucose levels were unaffected (P > 0.05). As such, glucose does not appear to be a reliable indicator of stress in Pallid Sturgeon. Defining the effects of stress on Pallid Sturgeon physiology is a critical first step toward understanding how stress affects fish health and well being and optimization of propagation practices.

Nutrient Contributions from Alluvial Soils Associated with the Restoration of Shallow Water Habitat in the Lower Missouri River

AbstractThe Missouri River has been extensively altered as the result of channelization, bank stabilization, and the construction of six main stem reservoirs. In response to the resultant habitat loss, the US Army Corps of Engineers was tasked with restoring approximately 8100 ha of shallow water habitat (SWH), in part, for the benefit of the endangered pallid sturgeon (Scaphirhynchus albus). Construction of off‐channel habitats involves the removal and disposal of excavated alluvium either by direct discharge into the river or by secondary erosion, which raised concerns regarding the introduction of sediment and associated nutrients into the Missouri River.Soils from nine side‐channel chutes were sampled to represent nutrient concentrations from habitat restoration activities. Soils from 12 historically undisturbed sites were also sampled to represent reference conditions in the Missouri River flood plain. The results of this study indicate that nutrient characteristics of soils from selected SWH locations generally are similar to those of historically undisturbed soils. The estimated mass of total phosphorus from chutes accounted for 1.9% of Missouri River and 0.5% of Mississippi River total phosphorus loads during the 1993–2012 analysis period. The mass of nitrate, the constituent most closely related to gulf hypoxia, was 0.01% or less of the Missouri and Mississippi River nitrate loads. Sediment volumes from the chutes accounted for 3.1 and 1.5% of total suspended loads from the Missouri and Mississippi Rivers. Overall, the introduced sediment from side‐channel chute construction associated with SWH restoration accounts for a small portion of total nutrient and sediment transport in the Missouri and Mississippi Rivers. Published 2014. This article is a U.S. Government work and is in the public domain in the USA. River Research and Applications published by John Wiley & Sons, Ltd.

Acute toxicity of sodium bicarbonate, a major component of coal bed natural gas produced waters, to 13 aquatic species as defined in the laboratory

Water produced during coal bed natural gas (CBNG) extraction in the Powder River Structural Basin of Wyoming and Montana (USA) may contain concentrations of sodium bicarbonate (NaHCO3) of more than 3000 mg/L. The authors evaluated the acute toxicity of NaHCO3, also expressed as bicarbonate (HCO3(-)), to 13 aquatic organisms. Of the 13 species tested, 7 had a median lethal concentration (LC50) less than 2000 mg/L NaHCO3, or 1300 mg/L HCO3(-). The most sensitive species were Ceriodaphnia dubia, freshwater mussels (Lampsilis siliquoidea), pallid sturgeon (Scaphirhynchus albus), and shovelnose sturgeon (Scaphirhynchus platorynchus). The respective LC50s were 989 mg/L, 1120 mg/L, 1249 mg/L, and 1430 mg/L NaHCO3, or 699 mg/L, 844 mg/L, 831 mg/L, and 1038 mg/L HCO3(-). Age affected the sensitivity of fathead minnows, even within life stage. Two days posthatch, fathead minnows were more sensitive to NaHCO3 and HCO3(-) compared with 4-d-old fish, even though fish up to 14 d old are commonly used for toxicity evaluations. The authors recommend that ion toxicity exposures be conducted with organisms less than 24 h posthatch to ensure that experiments document the most sensitive stage of development. The results of the present study, along with historical and current research regarding the toxicity of bicarbonate, may be useful to establish regulatory standards for HCO3(-). This article is a US Government work and is in the public domain in the USA.

Habitat Use and Selection by Adult Pallid Sturgeon in the Lower Mississippi River

AbstractThe Pallid Sturgeon Scaphirhynchus albus is an endangered riverine sturgeon with historical distribution restricted to the Yellowstone, Missouri, Mississippi, and Atchafalaya rivers. Although not abundant, Pallid Sturgeon in the lower Mississippi River appear to be naturally recruiting, and information about habitat use is important to conserve this species. Thirty‐four adult Pallid Sturgeon (612–1,013‐mm FL) were tagged with acoustic transmitters and relocated a total of 272 times in a 40‐km reach of the lower Mississippi River from April 2009 through December 2012. Pallid Sturgeon strongly selected island tip and natural bank habitats, and, to a lesser degree, revetted bank habitat. Although frequently used, Pallid Sturgeon exhibited negative selection for the expansive main channel habitat. Secondary channel habitat was seasonally available and excluded from habitat selection analysis, but this habitat was frequently used in the spring when available. Fifty percent of Pallid Sturgeon detections were in relatively narrow ranges of depths (6.2–13.6 m) and surface current velocities (0.64–1.05 m/s). Use of different habitats was related to river stage and water temperature, suggesting use of some habitats was seasonal. Results suggest that maintaining natural bank habitat and secondary channel–island complexes will benefit conservation of this endangered species in the lower Mississippi River.

Evaluating Growth, Survival and Swimming Performance to Determine the Feasibility of Telemetry for Age-0 Pallid Sturgeon (Scaphirhynchus albus)

Abstract Telemetry is valuable for understanding animal ecology and assessing conservation priorities. Sturgeon species worldwide are imperiled and telemetric methods have been applied to adults, but the feasibility of using this methodology on age-0 sturgeon remains unclear. The pallid sturgeon (Scaphirhynchus albus) is a federally endangered species in the central United States and little is known about its early life ecology. The use of telemetry on age-0 pallid sturgeon would greatly increase understanding of their early life ecology. We assessed growth, survival, and swimming performance of age-0 pallid sturgeon tagged with 0.2 g, nonfunctioning radio telemetry tags to determine whether radio telemetry can be used on such small sturgeon. Tags were surgically implanted internally and attached externally, with a control group that only experienced handling. Age-0 sturgeon with internally implanted tags grew slowly and had low survival, while counterparts within the control group and those with external...

Efficacy of AQUI‐S 20E as a Sedative for Handling and Cortisol Suppression in Pallid Sturgeon

AbstractChallenges and regulations associated with handling fish during fisheries management activities have increased efforts to achieve U.S. Food and Drug Administration approval for an immediate‐release sedative for fish. The objectives of this study were to (1) identify the target concentration of AQUI‐S 20E for sedation of Pallid Sturgeon Scaphirhynchus albus to a handleable state followed by rapid recovery, and (2) to compare sedation and recovery times and cortisol stress response in sturgeon treated with the identified target concentration to those treated with MS‐222. Juvenile Pallid Sturgeon from two size‐classes were exposed to five concentrations of AQUI‐S 20E: 70, 153, 364, 598, and 779 mg/L of water. The target concentrations of AQUI‐S 20E for optimal sedation (<3 min) and recovery times (<5 min) identified for Pallid Sturgeon were 476 mg/L for small and 537 mg/L for large size‐classes. Cortisol secretion in relation to presedation plasma cortisol levels was suppressed at the AQUI‐S 20E target concentration of 500 mg/L but was not for MS‐222. These data suggest an AQUI‐S 20E concentration of 500 mg/L is efficacious while blocking the cortisol stress response for sedation to a handleable state in Pallid Sturgeon.Received February 6, 2013; accepted July 24, 2013

Effect of Altering Dietary Protein: Energy Ratios on Juvenile Pallid Sturgeon Growth Performance

AbstractPallid Sturgeon Scaphirhynchus albus are endemic to the large, freshwater, river systems of North America and have long been prized for caviar production. Declining wild populations and fishing prohibitions have created interest in the culture of these fish. Protein and energy are often the first nutrients examined when attempting to identify diets appropriate for a novel culture species. Therefore, the present study evaluated the effects of different dietary protein: energy ratios on Pallid Sturgeon growth and body composition. Twelve semipurified diets composed of four crude protein (CP) levels (32, 39, 46, and 53%) and three gross energy (GE) levels (3,600, 4,200, and 4,800 kcal/kg) were fed to 180 juvenile Pallid Sturgeon for 18 weeks. Diets were offered to triplicate groups of five fish each in separate tanks. Fish were fed 2% body weight daily and sampled every 3 weeks. Mean weight gain and body composition were significantly affected by GE content of the dietary treatment (P ≤ 0.05), but not by dietary CP or protein and energy interactions (P > 0.05). The most energetically dense diets yielded significantly larger fish than the least energetically dense diets and the intermediate diets were not significantly different from either extreme. These results suggest that Pallid Sturgeon are able to perform similarly across a wide range of protein: energy ratios (79–147 mg protein/kcal), as long as adequate dietary energy (≥3,800 kcal GE/kg) is provided and essential amino acids are not limiting. This research is the first to evaluate dietary protein: energy ratios for Scaphirhynchus sturgeon culture.

The effect of temperature on embryo survival and development in pallid sturgeon Scaphirhynchus albus (Forbes & Richardson 1905) and shovelnose sturgeon S. platorynchus (Rafinesque, 1820)

The thermal response of pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon S. platorynchus embryos was determined at incubation temperatures from 8 to 26°C and 8 to 28°C, respectively. The upper and lower temperatures with 100% (LT100) embryo mortality were 8 and 26°C for pallid sturgeon and 8 and 28°C for shovelnose sturgeon. It was concluded that 12–24°C is the approximate thermal niche for embryos of both species. Generalized additive and additive-mixed models were used to analyze survival, developmental rate and dry weight data, and predict an optimal temperature for embryo incubation. Pallid sturgeon and shovelnose sturgeon embryo survival rates were different in intermediate and extreme temperatures. The estimated optimal temperature for embryo survival was 17–18°C for both species. A significant interaction between rate of development and temperature was found in each species. No evidence was found for a difference in timing of blastopore, neural tube closure, or formation of an S-shaped heart between species at similar temperatures. The estimated effects of temperature on developmental rate ranged from linear to exponential shapes. The relationship for rate of development to temperature was relatively linear from 12°C to 20°C and increasingly curvilinear at temperatures exceeding 20°C, suggesting an optimal temperature near 20°C. Though significant differences in mean dry weights between species were observed, both predicted maximum weights occurred at approximately 18°C, suggesting a temperature optimum near 18°C for metabolic processes. Using thermal optimums and tolerances of embryos as a proxy to estimate spawning distributions of adults in a river with a naturally vernalized thermal regime, it is predicted that pallid sturgeon and shovelnose sturgeon spawn in the wild from 12°C to 24°C, with mass spawning likely occurring from 16°C to 20°C and with fewer individuals spawning from 12 to 15°C and 21 to 24°C. Hypolimnetic releases from Missouri River dams were examined; it was concluded that the cooler water has the potential to inhibit and delay sturgeon spawning and impede embryo incubation in areas downstream of the dams. Further investigations into this area, including potential mitigative solutions, are warranted.

Vulnerability of age-0 pallid sturgeon Scaphirhynchus albus to predation; effects of predator type, turbidity, body size, and prey density

Predation can play an important role in the recruitment dynamics of fishes with intensity regulated by behavioral (i.e., prey selectivity) and/or environmental conditions that may be especially important for rare or endangered fishes. We conducted laboratory experiments to quantify prey selection and capture efficiency by three predators employing distinct foraging strategies: pelagic piscivore (walleye Sander vitreus); benthic piscivore (flathead catfish Pylodictis olivaris) and generalist predator (smallmouth bass Micropterus dolomieu) foraging on two size classes of age-0 pallid sturgeon: large (75–100 mm fork length [FL]) and small (40–50 mm FL). Experiments at high (> 70 nephalometric turbidity units [NTU]) and low (< 5 NTU) turbidity for each predator were conducted with high and low densities of pallid sturgeon and contrasting densities of an alternative prey, fathead minnow Pimephales promelas. Predator behaviors (strikes, captures, and consumed prey) were also quantified for each prey type. Walleye and smallmouth bass negatively selected pallid sturgeon (Chesson’s α = 0.04–0.1) across all treatments, indicating low relative vulnerability to predation. Relative vulnerability to predation by flathead catfish was moderate for small pallid sturgeon (α = 0.44, neutral selection), but low for large pallid sturgeon (α = 0.11, negative selection). Turbidity (up to 100 NTU) did not affect pallid sturgeon vulnerability, even at low density of alternative prey. Age-0 pallid sturgeon were easily captured by all predators, but were rarely consumed, suggesting mechanisms other than predator capture efficiency govern sturgeon predation vulnerability.

Population prediction and viability model for pallid sturgeon (Scaphirhynchus albus , Forbes and Richardson, ) in the lower Missouri River

Long-term population trends of pallid sturgeon Scaphirhynchus albus in the lower Missouri River were evaluated via a discrete and stochastic age-structure population viability model. The intent of this model was to (i) estimate the local pallid sturgeon population size, (ii) quantify the contribution of hatchery-reared fish to the overall population, (iii) predict the level of natural production needed to create a self-sustaining population, and (iv) determine the parameters that produce the largest model sensitivity. The model estimated that the wild, adult population size was approximately 6000 fish that remained in the lower Missouri River in 2012 compared to approximately 42 000 hatchery-reared pallid sturgeon. Under the assumption of no natural recruitment, the population size will continue to decline at approximately 8% annually, with an annual egg to age-1 survival rate of 0.00011 predicted to maintain a stable population. The model was most sensitive to survival rates of fish ≥ age-1 and less sensitive to age-0 survival rates and fecundity. Decreasing or increasing the female spawning interval by 1 year had minimal effect on the overall population trajectory. Recovery management planning for a species such as pallid sturgeon, which is slow-growing, late-maturing, and has intermittent spawning would require several years to access recovery potential and management decisions. Barring any unforeseen natural catastrophe, the pallid sturgeon population in the lower Missouri River is not in immediate danger of local extirpation; however, the population appears to be far from viable and self-sustaining.

Size-Dependent Trophic Patterns of Pallid Sturgeon and Shovelnose Sturgeon in a Large River System

Abstract This study compared patterns of δ15N and δ13C enrichment of pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon S. platorynchus in the Missouri River, United States, to infer their trophic position in a large river system. We examined enrichment and energy flow for pallid sturgeon in three segments of the Missouri River (Montana/North Dakota, Nebraska/South Dakota, and Nebraska/Iowa) and made comparisons between species in the two downstream segments (Nebraska/South Dakota and Nebraska/Iowa). Patterns in isotopic composition for pallid sturgeon were consistent with gut content analyses indicating an ontogenetic diet shift from invertebrates to fish prey at sizes of &amp;gt;500-mm fork length (FL) in all three segments of the Missouri River. Isotopic patterns revealed shovelnose sturgeon did not experience an ontogenetic shift in diet and used similar prey resources as small (&amp;lt;500-mm FL) pallid sturgeon in the two downstream segments. We found stable isotope analysis to be an effective tool for evaluating the trophic position of sturgeons within a large river food web.

Gonadosomatic index and fecundity of Lower Missouri and Middle Mississippi River endangered pallid sturgeon estimated using minimally invasive techniques

Summary Minimally invasive, non-lethal methods of ultrasonography were used to assess sex, egg diameter, fecundity, gonad volume, and gonadosomatic index, as well as endoscopy to visually assess the reproductive stage of Scaphirhynchus albus. Estimated mean egg diameters of 2.202 ± 0.187 mm and mean fecundity of 44 531 ± 23 940 eggs were similar to previous studies using invasive techniques. Mean S. albus gonadosomatic indices (GSI) for reproductive and non-reproductive females were 16.16 and 1.26%, respectively, while reproductive and non-reproductive male GSI were 2.00 and 0.43%, respectively. There was no relationship between hybrid status or capture location and GSI. Mean fecundity was 48.5% higher than hatchery spawn estimates. Fecundity increased as fork length increased but did so more dramatically in the upper river kilometers of the Missouri River. By examining multiple fish over multiple years, the reproductive cycle periodicity for hatchery female S. albus was found to be 2–4 years and river dwelling males 1–4 years. The use of ultrasonic and endoscopic methods in combination was shown to be helpful in tracking individual gonad characteristics over multi-year reproductive cycles.

Population characteristics of pallid sturgeon (Scaphirhynchus albus (Forbes &amp; Richardson, )) in the Lower Missouri River

Population characteristics of pallid sturgeon Scaphirhynchus albus in the lower Missouri River are relatively unknown. Therefore, data collected from the Nebraska Game and Parks Commission Pallid Sturgeon Population Assessment Program was synthesized to (i) document the population structure of pallid sturgeon by origin (hatchery-reared or wild), gender, and reproductive readiness, (ii) document the minimum size and age-at-maturity by gender, and (iii) document the fecundity rates of the fish that were successfully spawned in the hatchery. During this 4-year study (2008–2011), relative abundance for wild and hatchery-reared pallid sturgeon collected with gill nets did not significantly change whereas relative abundance for wild fish using trot lines declined significantly. The proportion of hatchery-reared pallid sturgeon increased annually, with the population being composed primarily of hatchery-reared fish. The proportion of reproductively ready females to non-reproductively ready females was 1 : 2.0, compared to male ratios at 1 : 0.9. Minimum fork length-at-maturity was estimated for females at 788 mm and for males at 798 mm. Minimum age-at-maturity for hatchery-reared released fish was age-9 for females and age-7 for males. Highest relative fecundity, based on the ovosomatic index, was 10% with an overall mean of 7%. The number of eggs per ml (egg size) was not correlated with fork length (P = 0.0615) or weight (P = 0.0957). Relative condition factor (Kn) for females was significantly different by reproductive condition (P = 0.0014) and Kn for males did not differ between reproductive conditions (P = 0.2634). Detecting shifts in population characteristics are essential not only to understand population dynamics since hatchery inputs and natural perturbations continue to change the population structure but also to assess species recovery efforts to ensure long-term species sustainability.

Observations on the Identification of Larval and JuvenileScaphirhynchusspp. in the Lower Mississippi River

Abstract Scaphirhynchus albus (Pallid Sturgeon) and S. platorynchus (Shovelnose Sturgeon) are sympatric and not uncommon in the lower Mississippi River from the confluence of the Ohio River to the Gulf of Mexico, and in its distributary, the Atchafalaya River. Reports of sturgeon larvae have been rare in the Mississippi River but have been increasing with more effective collection methods. A suite of characters identified in hatchery-reared larval Pallid Sturgeon and Shovelnose Sturgeon from the Yellowstone and upper Missouri rivers has been used to distinguish larval Scaphirhynchus spp. In the Mississippi River; however, a large proportion of wild Scaphirhynchus spp. larvae are intermediate in these characters and have been identified by some as hybridized Pallid Sturgeon and Shovelnose Sturgeon. We applied three diagnostic characters developed from Missouri River sturgeon larvae to hatchery-reared progeny of Atchafalaya River Pallid Sturgeon and found them inadequate to identify most of the known Pallid...