Post‐stocking pallid sturgeon Scaphirhynchus albus growth,dispersal, and survival in the lower Missouri River

Hatchery augmentation has been used to mitigate declines in fish populations worldwide, especially for sturgeon species. Information regarding stocking success including survival, dispersal, and growth of sturgeon post‐stocking may refine sturgeon augmentation programs and facilitate recovery. Pallid sturgeon Scaphirhynchus albus populations have been supplemented by hatchery‐reared stocks for 25 years in the Missouri River, USA. We assessed survival, dispersal patterns, and growth characteristics of post‐stocked pallid sturgeon in the lower Missouri River. Hatchery‐reared pallid sturgeon stocked at age‐1 (4.1%) and > age‐1 (2.9%) were recaptured at a higher frequency than fish stocked at age‐0 (0.3%). Post‐stocking dispersal patterns suggested dispersal range increase as age increased, but individuals tended to remain in the same river segment as their stocking location. Growth rates varied by year class with younger year classes having truncated growth trajectories compared to older year classes. Post‐stock survival of pallid sturgeon varied by age‐at‐stocking and suggest age‐1 survival has declined through time. Augmentation of pallid sturgeon may benefit from considering dispersal from stocking location and by stocking older individuals which appear to have increased survival post‐stocking. A better understanding regarding environmental drivers of growth and specific habitat features used is needed to better predict optimal timing and location of future stockings.     

Updated assessment of hatchery‐reared pallid sturgeon (Forbes & Richardson, 1905) survival in the lower Missouri River

As pallid sturgeon, Scaphirhynchus albus (Forbes & Richardson, 1905), natural reproduction and recruitment remains very minimal in the lower Missouri River from Gavins Point Dam (river kilometer [rkm] 1305.2) to the confluence with the Mississippi River (rkm 0.0), hatchery supplementation and river‐wide monitoring efforts have continued. Annual survival estimates of hatchery‐reared pallid sturgeon stocked in the lower Missouri River were previously estimated during 1994–2008. Low recapture rates prior to 2006 limited the data available to estimate survival, which resulted in considerable uncertainty for the estimate of annual survival of age‐1 fish. Therefore, the objective was to provide more precise estimates of annual survival of pallid sturgeon using five additional years of stocking and sampling. The Cormack‐Jolly‐Seber model structure provided in program MARK was used to estimate the age‐specific survival estimates. Over 135 000 hatchery‐reared pallid sturgeon were released during 1994–2011 and recaptured at a rate of 1.9%, whereby estimates for the annual survival of age‐0 (Ø = 0.048) and >age‐1 (Ø = 0.931) were similar to those previously reported, but the age‐1 (Ø = 0.403) survival estimate was 52% lower. Post hoc analysis using time‐specific survival estimates indicated lower survival for age‐1 fish post‐2003 year classes, relative to the pre‐2002 year classes. An analysis confirms that hatchery‐reared pallid sturgeon continue to survive in the wild. However, low survival during the first 2 years of life is a management concern as efforts are aimed at maximizing genetic diversity and population growth. A follow‐up analysis also demonstrated the variability of capture rates and survival over time, which reinforces the need to continue to monitor and evaluate mark‐recapture data. The mark‐recapture efforts have provided demographic parameter estimates that remain a critical component for species recovery as these data are incorporated into population models.     

Age and growth of pallid sturgeon in the free-flowing Mississippi River

Trotlines were used to capture pallid sturgeon in the free‐flowing Mississippi River, which extends from the Gulf of Mexico to the mouth of the Missouri River. Trotlines were baited with worms, and set overnight usually along the channel border. The pectoral fin rays of 165 pallid sturgeon caught in the Mississippi River were aged; 118 were from the lower Mississippi River (LMR) between the Gulf and mouth of the Ohio River, and 47 were from the middle Mississippi River (MMR) between the mouths of the Ohio and Missouri rivers. Initial agreement within ±1 year between two readers ranged from 53% for the LMR specimens, which were read first, to 84% for the MMR. Final age was agreed upon by both readers. For LMR pallid sturgeon, final age estimates ranged from 3 to 21 years with a mean (±SD) of 11.0 ± 4.7. For MMR pallid sturgeon, final age estimates ranged from 5 to 14 years with a mean of 9.5 ± 2.1. Seven pallid sturgeon marked with coded wire tags (CWT), indicating hatchery origin, were collected in the MMR. Age estimates for CWT fish were 7–8 years representing 1997 stocked fish, and 11–12 years representing 1992 progeny stocked in 1994. Von Bertalanffy growth equations for length indicated that pallid sturgeon in the MMR had higher growth rates for a given age than pallid sturgeon in the LMR. However, there were no significant differences (anova , P > 0.5) in the length–weight relationships between reaches. In the LMR, pallid sturgeon fully recruited to trotlines at age 11 and instantaneous total mortality (Z; slope of catch curve) was estimated at −0.12 (n = 10 year classes, r² = 0.55, P = 0.01). Of the 118 sectioned rays from the LMR, 28 could not be reliably aged (only one section from the MMR could not be aged). Therefore, age was predicted from length using the von Bertalanffy equation. The catch curve was re‐calculated using the predicted ages of the 28 pallid sturgeon in the LMR resulting in Z = −0.07. In the MMR, pallid sturgeon fully recruited to trotlines at age 9 and Z was estimated at −0.36 (n = 6 year classes, r² = 0.67, P = 0.04), which was significantly higher (anova , P = 0.04) than the LMR estimate. Higher mortality in the MMR may be due to habitat limitations compared to a larger, more diverse channel in the LMR, and incidental take of larger, older individuals during commercial harvesting of shovelnose sturgeon. Commercial take of shovelnose does not occur in the LMR except in the northern portion of the reach. Considering the presence of pallid sturgeon with CWT, recruitment of older individuals in the MMR may have been influenced by stocking a decade earlier. Management strategies for this endangered species should consider the differences in mortality rates among reaches, the impacts of commercial fishing on recovery of pallid sturgeon in the MMR, and the long‐term effects of hatchery fish now recruiting into the free‐flowing Mississippi River.     

Cohort‐specific estimates of first‐year survival are positively associated with size at stocking for lake sturgeon Acipenser fulvescens (Rafinesque 1817) stocked in Black Lake,Michigan, USA

The authors conducted a gillnet survey in 2013 in Black Lake, Michigan, USA to evaluate the lake sturgeon (Acipenser fulvescens) stocking programme that began in 2001. Objectives were to (i) estimate year‐class specific abundance of juvenile lake sturgeon in Black Lake; and (ii) determine year‐class specific survival of stocked year classes and determine whether year‐class‐specific first‐year survival was related to average size at the time of stocking. Deployed were 15 and 20 cm stretch mesh gillnets at 72 randomly selected sites in Black Lake over a 3‐week survey using a Schnabel multiple‐mark, multiple‐recapture estimator to determine overall abundance of stocked fish. Ages for captured fish were determined from fin ray cross sections and the presence of coded wire tags, and apportioned the overall abundance estimate of juveniles to year class using an age‐length key. Overall survival estimates were calculated by dividing the year‐class specific abundance estimates by the number of fish stocked that year. Also evaluated was the relationship between first‐year survival and average total length (TL) at time of stocking using logistic regression. Overall survival from stocking to 2013 ranged from 0.03 to 0.53. First‐year survival was positively associated with average TL at stocking, and ranged from 0.05 for fish stocked at 9 cm TL to 0.84 for fish stocked at 22 cm TL. Estimation of future cohort‐specific abundance based on size‐based expected survival allows managers to establish annual stocking targets that should lead to the achievement of long‐term population goals for adult abundance.     

Natural growth and diet of known‐age pallid sturgeon (Scaphirhynchus albus) early life stages in the upper Missouri River basin,Montana and North Dakota

Prior to anthropogenic modifications, the historic Missouri River provided ecological conditions suitable for reproduction, growth, and survival of pallid sturgeon Scaphirhynchus albus. However, little information is available to discern whether altered conditions in the contemporary Missouri River are suitable for feeding, growth and survival of endangered pallid sturgeon during the early life stages. In 2004 and 2007, nearly 600 000 pallid sturgeon free embryos and larvae were released in the upper Missouri River and survivors from these releases were collected during 2004–2010 to quantify natural growth rates and diet composition. Based on genetic analysis and known‐age at release (1–17 days post‐hatch, dph), age at capture (dph, years) could be determined for each survivor. Totals of 23 and 28 survivors from the 2004 and 2007 releases, respectively, were sampled. Growth of pallid sturgeon was rapid (1.91 mm day^?1) during the initial 13–48 dph, then slowed as fish approached maximum length (120–140 mm) towards the end of the first growing season. The diet of young‐of‐year pallid sturgeon was comprised of Diptera larvae, Diptera pupae, and Ephemeroptera nymphs. Growth of pallid sturgeon from ages 1–6 years was about 48.0 mm year^?1. This study provides the first assessment of natural growth and diet of young pallid sturgeon in the wild. Results depict pallid sturgeon growth trajectories that may be expected for naturally produced wild stocks under contemporary habitat conditions in the Missouri River and Yellowstone River.     

Evaluation of passive integrated transponder tag retention from two tagging locations in juvenile pallid sturgeon

Population augmentation and propagation of pallid sturgeon (Scaphirhynchus albus) have been a focus of scientists since the mid‐1990s. Various tag types have been used to gain a better understanding of population characteristics, stocking success, and movement patterns. Passive integrated transponder (PIT) tags have been consistently used since the inception of recovery efforts to mark age‐1 and older pallid sturgeon. This tag has been successfully used with other sturgeon species, and tagging protocols for pallid sturgeon were developed in response to those successes. Tag retention rates in pallid sturgeon have been reported as variable or unknown and there has been no formal study to determine PIT tag retention in pallid sturgeon, particularly with age‐1 individuals that are propagated in hatcheries to be stocked into the wild. The objective was to evaluate retention rates of PIT tags inserted into the operculum and along the base of the dorsal fin of age‐1 pallid sturgeon (total fork length [FL] range = 214–358 mm). Tagged sturgeon (n = 80) were held in a large holding tank and inspected for tag loss twice a month for a total of 189 days. Final tag retention was 83% for tags inserted into the operculum and 85% for tags inserted near the dorsal fin. Tags shed from the operculum were from smaller fish (mean FL = 265 mm) and losses occurred during the first 60 days of the experiment. Tags shed from the dorsal site were predominantly from larger individuals (mean FL = 305 mm) and losses were continual throughout the experiment. Future research should determine size‐specific tag retention rates so that hatcheries can maximize retention in either tag placement location.     

Ontogenetic patterns in prey use by pallid sturgeon in the Missouri River, South Dakota and Nebraska

The pallid sturgeon ( Scaphirhynchus albus ) is an endangered species native to the Missouri and Mississippi rivers. To date, recovery efforts have focused on stocking juvenile fish, but little is known about ontogenetic changes in diet composition. Although diet composition for pallid sturgeon is believed to change from macroinvertebrates to fish, it is unclear at what size and/or age these ontogenetic diet shifts occur. To evaluate diet composition, 29 hatchery-stocked pallid sturgeon (range 356–720 mm fork length [FL]; mean = 549; SE = 23) were collected from the Missouri River downstream of Fort Randall Dam, South Dakota and Nebraska during summer 2006. The majority of pallid sturgeon (72%) were captured within a large delta region formed by the Niobrara River in the headwaters of Lewis and Clark Lake. Predominant prey of pallid sturgeon based on percent occurrence was Ceratopogonidae (81%), Isonychiidae (67%), Chironomidae (52%), and fishes (24%). Percent composition by wet weight showed that diets were composed of fishes (68%), Ephemeroptera (23%), Decapoda (6%), and Diptera (3%). Graphical analysis of combined data showed that mayflies, particularly Isonychiidae, were an important component of pallid sturgeon diets. Nonetheless, the percent composition of fishes in the diet increased with pallid sturgeon body size; for fish > 600 mm FL (5–7 years of age) diets were composed primarily of fish prey (66%, mostly johnny darters Etheostoma nigrum ). These findings highlight the importance of ontogenetic changes in diet composition for pallid sturgeon. Moreover, the unique habitat formed in the delta region is characterized by higher fish and invertebrate densities that may enhance foraging opportunities and thus improve recovery efforts for stocked pallid sturgeon.     

Resource selection by juvenile pallid sturgeon Scaphirhynchus albus (Forbes and Richardson, 1905) in the channelized Missouri River,Nebraska, USA

Habitat selection has been quantified for age‐0 and adult pallid sturgeon Scaphirhynchus albus Bull. Illinois State Lab. Nat. Hist., 7, 1905, 37, but little is known regarding habitat use of the juvenile fish. The objective of this study was to quantify habitat use and selection of juvenile pallid sturgeon in the Missouri River, Nebraska, USA. Thirty‐seven age‐4 pallid sturgeon with transmitters were released in July of 2014, plus an additional 21 in September, with habitat monitored using biotelemetry. Age‐1 and age‐4 hatchery reared pallid sturgeon were found to avoid areas associated with the outside bend and thalweg habitats that were characterized by rapid water velocity (>1 ms^?1), which accounted for 50% of the area in the channelized Missouri River. Age‐1 pallid sturgeon selected an off‐channel habitat and inside bend habitat while age‐4 pallid sturgeon selected an off‐channel and inside bend channel border habitat. Juvenile pallid sturgeon in unaltered rivers have been shown to associate with island tips and sand bars, habitat that is largely absent in the channelized Missouri River. This study indicates that juvenile pallid sturgeon in the Missouri River, Nebraska are selecting habitats with shallow water and slow water velocity, similar to those associated with island tips and sand bars in unaltered reaches.     

The effect of stocking with 0+ year age‐class Atlantic salmon Salmo salar fry: a case study from the River Bush,Northern Ireland

An enhancement programme based on stocking 0+ year age‐class Atlantic salmon Salmo salar, conducted in the River Bush, Northern Ireland, U.K. over the period 1996–2005, was reviewed with reference to the performance and biological characteristics of wild fish. Wild ova to 0+ year fry (summer) survival was c. 8% with subsequent wild 0+ year fry‐to‐smolt survival c. 9%. Stocked unfed 0+ year juveniles gave c. 1% survival to smolt whilst fed 0+ year S. salar stocked in late summer exhibited survival at c. 5%. Stocking with unfed and fed fry contributed to increased smolt production and helped attain local management objectives between 2001 and 2005. Significant differences in biological characteristics were observed between wild and stocked‐origin fish. Wild‐smolt cohorts were dominated by 2+ year age‐class fish on the River Bush whilst smolts originating from fed fry mostly comprised younger 1+ year individuals. The mean mass of 1+ year smolts derived from stocked fed fry was significantly lower than that of wild 1+ year smolts, although these differences were not evident between older age classes. Differences in run timing between wild smolts and smolts derived from stocked fry were also apparent with the stocked‐origin fish tending to run earlier than wild fish. Although the stocking exercise was useful in terms of maximizing freshwater production, concerns over the quality of stocked‐origin recruits and the long term consequences for productivity are highlighted.     

Population viability analysis of Lower Missouri River shovelnose sturgeon with initial application to the pallid sturgeon

Demographic models for the shovelnose (Scaphirhynchus platorynchus) and pallid (S. albus) sturgeons in the Lower Missouri River were developed to conduct sensitivity analyses for both populations. Potential effects of increased fishing mortality on the shovelnose sturgeon were also evaluated. Populations of shovelnose and pallid sturgeon were most sensitive to age‐0 mortality rates as well as mortality rates of juveniles and young adults. Overall, fecundity was a less sensitive parameter. However, increased fecundity effectively balanced higher mortality among sensitive age classes in both populations. Management that increases population‐level fecundity and improves survival of age‐0, juveniles, and young adults should most effectively benefit both populations. Evaluation of reproductive values indicated that populations of pallid sturgeon dominated by ages ≥35 could rapidly lose their potential for growth, particularly if recruitment remains low. Under the initial parameter values portraying current conditions the population of shovelnose sturgeon was predicted to decline by 1.65% annually, causing the commercial yield to also decline. Modeling indicated that the commercial yield could increase substantially if exploitation of females in ages ≤12 was highly restricted.     

First maturity and spawning periodicity of hatchery‐origin pallid sturgeon in the upper Missouri River above Fort Peck Reservoir,Montana

The pallid sturgeon Scaphirhynchus albus conservation propagation program has augmented declining wild populations since the 1990s and the older age classes of hatchery‐origin fish are beginning to reach sexual maturity in the wild. Currently, the majority of the information available on the age and size at first maturity and spawning periodicity for pallid sturgeon in the upper basin is from captive hatchery‐origin pallid sturgeon (i.e. age and size at first maturity and spawning periodicity) or from wild pallid sturgeon artificially spawned in the propagation program (i.e. spawning periodicity). The purpose of this study was to document age and size at first maturity and spawning periodicity of known age hatchery‐origin pallid sturgeon that have reached maturity in the wild. Radio‐tagged pallid sturgeon in the upper Missouri River upstream of Fort Peck Reservoir were serially sampled in the early‐spring over multiple years and assigned to reproductive classifications each year based on sex‐steroid concentrations. The youngest reproductively‐active male hatchery‐origin pallid sturgeon sampled was 14.5 years old and the youngest female was 18. Hatchery‐origin males were observed having annual (N = 3) and biennial (N = 2) reproductive cycles. The observed spawning periodicity was similar to what has been reported elsewhere for the species. The youngest mature fish in this study are older and larger than what has been reported for those retained in captivity, indicating that body size alone is not a reliable predictor of maturity for pallid sturgeon.     

An experimental test and models of drift and dispersal processes of pallid sturgeon (<Emphasis Type="Italic">Scaphirhynchus albus</Emphasis>) free embryos in the Missouri River

Free embryos of wild pallid sturgeon Scaphirhynchus albus were released in the Missouri River and captured at downstream sites through a 180-km reach of the river to examine ontogenetic drift and dispersal processes. Free embryos drifted primarily in the fastest portion of the river channel, and initial drift velocities for all age groups (mean = 0.66–0.70 m s⁻¹) were only slightly slower than mean water column velocity (0.72 m s⁻¹). During the multi-day long-distance drift period, drift velocities of all age groups declined an average of 9.7% day⁻¹. Younger free embryos remained in the drift upon termination of the study; whereas, older age groups transitioned from drifting to settling during the study. Models based on growth of free embryos, drift behavior, size-related variations in drift rates, and channel hydraulic characteristics were developed to estimate cumulative distance drifted during ontogenetic development through a range of simulated water temperatures and velocity conditions. Those models indicated that the average free embryo would be expected to drift several hundred km during ontogenetic development. Empirical data and model results highlight the long-duration, long-distance drift and dispersal processes for pallid sturgeon early life stages. In addition, results provide a likely mechanism for lack of pallid sturgeon recruitment in fragmented river reaches where dams and reservoirs reduce the length of free-flowing river available for pallid sturgeon free embryos during ontogenetic development.     

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.     

Range‐wide assessment of pallid sturgeon Scaphirhynchus albus (Forbes & Richardson, 1905) relative condition

Pallid sturgeon Scaphirhynchus albus relative condition has been observed to be declining along the Nebraska reach (rkm 1212.6–801.3) of the Missouri River over the past several years; therefore, pallid sturgeon capture data was synthesized from the entire Missouri and Middle Mississippi rivers to document and compare how pallid sturgeon condition varies spatially and temporally throughout much of their current range. The study area was subdivided into four river reaches based on a priori statistical differences for pallid sturgeon catches from 2003 to 2015. Pallid sturgeon in the Middle Mississippi River (Alton Dam [rkm 321.9]) to the confluence of the Ohio River (rkm 0.0) were in the best condition while pallid sturgeon in the Middle Missouri River (Fort Randall Dam [rkm 1416.2]) to the Grand River confluence (rkm 402.3) were in the poorest condition. Furthermore, pallid sturgeon condition in the Upper Missouri River (Fort Peck Dam [rkm 2850.9] to the headwaters of Lake Sakakawea [rkm 2523.5] and lower Yellowstone River) and the Lower Missouri River (Grand River confluence to the Mississippi River confluence [rkm 0.0]) were significantly less than in the Middle Mississippi River but significantly higher than the Middle Missouri River. Temporally, pallid sturgeon condition was highly variable. Relative condition in the Middle Mississippi River was consistently above average (Kn = 1.1). Comparatively, Kn throughout the Missouri River rarely exceeded “normal” (Kn = 1.0), with Kn in the middle and lower reaches of the Missouri River having declined to the lowest observed. As pallid sturgeon recovery efforts continue, understanding the range‐wide differences and effects on condition could be critical, as poor condition may cause maturation delays, reproductive senescence or even mortality, which affects the likelihood of natural reproduction and recruitment.     

Evaluation of pulsed gastric lavage on the survival of captive shovelnose sturgeon

Little is known about the diet of the endangered pallid sturgeon, Scaphirhynchus albus. Because of this endangered status non‐lethal methods to ascertain their food habits must be evaluated. Tests of pulsed gastric lavage (PGL) were conducted on shovelnose sturgeon S. platorynchus, as a surrogate for the pallid sturgeon, to determine if PGL negatively affected their survival. Nine sequential trials containing eight shovelnose sturgeon (N = 72) were conducted with wild fish collected from the Platte River near Louisville, Nebraska. Each trial group was placed into one of two tanks, with each tank containing three pulsed gastric lavaged fish and one control fish. Fish were weighed, measured, and tagged with a passive integrated transponder (PIT tag) before being transported to holding tanks for acclimation and PGL treatment. Sturgeon were acclimated 4–6 days prior to PGL, then held for 15 days after treatment. Temperature, dissolved oxygen, ammonia, and nitrite were monitored daily. No significant difference between the survival of PGL fish and control fish was detected. Because the test required these fish to endure the additional stress of transport and handling, PGL seems a viable technique that can be safely used to evaluate food habits of shovelnose sturgeon, and could be considered safe for pallid sturgeon food habit studies.     

Stock structure of pallid sturgeon analyzed with microsatellite loci

Recovery efforts for the endangered pallid sturgeon (Scaphirhynchus albus) include supplementation of wild stocks with hatchery reared progeny. Identifying the extent of genetic stock structure, which has previously been detected in samples from the range extremes, will help to determine whether stock transfers might be harmful. DNA microsatellite genotypes were screened in pallid sturgeon from the upper Missouri River, lower Missouri River, middle Mississippi River and Atchafalaya River and analyzed using a combination of Bayesian model‐based and more traditional F‐statistic based methods to characterize genetic differentiation. Scaphirhynchus specimens were collected by researchers active in the recovery effort and genotypes were screened at 16 microsatellite loci. Because there is considerable genetic and morphological overlap between pallid sturgeon, shovelnose sturgeon, and their hybrids, a combination of morphological and genetic techniques were used to eliminate shovelnose and possible hybrids from the sample. Genetic differentiation was detected among samples (overall θ = 0.050, P = 0.001). Pairwise θ, genetic distances, and Bayesian assignment testing reveal that pallid sturgeon from the upper Missouri River are the most distinct group with pairwise comparisons of pallid sturgeon among all the remaining samples exhibiting lower θ values, higher genetic distances, and self assignment scores. Our results indicate that using local broodstock, when available, should be used for pallid sturgeon propagation. If local broodstock are not available, geographically proximate individuals would limit genetic differences between native and stocked individuals.     

Reproductive ecology and movement of pallid sturgeon in the upper Missouri River,Montana

Successful recruitment of endangered pallid sturgeon has not been documented in the upper Missouri River basin for decades, and research on the reproductive ecology of pallid sturgeon has been hindered by low sample size. A conservation propagation program was initiated in the 1990s, and the oldest age class of hatchery‐origin pallid sturgeon are becoming sexually mature increasing the number of reproductively‐active fish in the system. However, it is currently unknown how the reproductive ecology of hatchery‐origin pallid sturgeon relates to the few remaining wild fish. Following spring reproductive assessments, weekly relocations were recorded for each individual from late‐May to mid‐July to facilitate comparisons of spawning season movements among reproductive classifications and between spring hydrographs (2015 and 2016) for male pallid sturgeon. Mean total movement distances (±SE) were 104.5 km (18.9) for reproductively‐active wild males, 116.0 km (18.1) for reproductively‐active 1997‐year class males, and 20.6 km (3.0) for non‐reproductively‐active fish of unconfirmed sex. Movement characteristics of reproductively‐active males did not differ between 2015 and 2016 despite a difference of eight days in the timing of peak discharge and a difference of 79 m³/s (16.7%) in magnitude. Male aggregations were observed on the descending limb of the hydrograph in 2016 during temperatures suitable for spawning, but female pallid sturgeon underwent follicular atresia, similar to the other years of the study. Hatchery‐origin pallid sturgeon from the conservation propagation program appear to have retained reproductive characteristics from the wild broodstock, a key finding for a population where local extirpation of the wild stock is imminent.     

Application of non‐lethal stable isotope analysis to assess feeding patterns of juvenile pallid sturgeon Scaphirhynchus albus: a comparison of tissue types and sample preservation methods

Traditional techniques for stable isotope analysis (SIA) generally require sacrificing animals to collect tissue samples; this can be problematic when studying diets of endangered species such as the pallid sturgeon Scaphirhynchus albus. Our objectives were to (i) determine if pectoral fin tissue (non‐lethal) could be a substitute for muscle tissue (lethal) in SIA of juvenile pallid sturgeon, and (ii) evaluate the influence of preservation techniques on stable isotope values. In the laboratory, individual juvenile pallid sturgeon were held for up to 186 day and fed chironomids, fish, or a commercially available pellet diet. Significant, positive relationships (r² ≥ 0.8) were observed between fin and muscle tissues for both δ¹⁵N and δ¹³C; in all samples isotopes were enriched in fins compared to muscle tissue. Chironomid and fish based diets of juvenile pallid sturgeon were distinguishable for fast growing fish (0.3 mm day^?1) using stable δ¹⁵N and δ¹³C isotopes. Frozen and preserved fin tissue δ¹⁵N isotopes were strongly related (r² = 0.89) but δ¹³C isotopes were weakly related (r² = 0.16). Therefore, freezing is recommended for preservation of fin clips to avoid the confounding effect of enrichment by ethanol. This study demonstrates the utility of a non‐lethal technique to assess time integrated food habits of juvenile pallid sturgeon and should be applicable to other threatened or endangered species.     

Potential responses of the Lower Missouri River Shovelnose Sturgeon (Scaphirhynchus platorynchus) population to a commercial fishing ban

We developed an age‐structured population matrix model to perform population viability analysis for Lower Missouri River (LMR) shovelnose sturgeon (Scaphirhynchus platorynchus). We investigated potential effects of the commercial fishing moratorium put in place to help protect the similar‐appearing pallid sturgeon (S. albus). The model applies different components of total variance in life history parameters at different levels: sampling variance (parameter uncertainty) between model iterations; temporal variance (temporal environmental fluctuations) between time steps within iterations; and individual variance (individual differences) within each time‐step. The model predicted annual rates of population increase of 1.96% under historic fishing and 2.67% with removal of historic fishing. We identified combinations of fishing and harvest size restrictions that would permit a sustainable harvest of shovelnose sturgeon. Overall, the ban on commercial fishing of shovelnose sturgeon in the LMR due to similarity of appearance to pallid sturgeon should help the LMR shovelnose sturgeon population begin to rebound while decreasing any negative effects it may have had on pallid sturgeon populations.     

Growth and contribution of stocked channel catfish,Ictalurus punctatus (Rafinesque, 1818): the importance of measuring post‐stocking performance

In this study it was sought to quantify post‐stocking growth, survival, and contribution of advanced size (178 mm total length [TL]) channel catfish Ictalurus punctatus fingerlings, something rarely done. Channel catfish populations were evaluated before (May 2010) and after (May to August 2011 and 2012) stocking. Relative abundance, stocking contribution, and growth were different (P < 0.05) in the two study impoundments (lakes Lone Chimney and Greenleaf, Oklahoma). For fish stocked in Lake Lone Chimney, stocking contribution was lower (3–35%), and average length and weight of stocked fish by age‐2 reached 230 mm TL and 85 g, whereas the stocking contribution (84–98%) and growth in length (340 mm TL) and weight (280 g) were higher by age‐2 in Lake Greenleaf. Given these unambiguous differences of post‐stocking performance, benchmark metrics that represent population‐level information such as relative abundance and average length and weight of the sample masked these significant differences, highlighting the importance of marking hatchery‐fish and then following them through time to determine the effectiveness of stocking. These results suggest that stock enhancement programmes would benefit from studies that quantify post‐stocking performance of hatchery fish.