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We used mark-recapture data from shovelnose sturgeon (Scaphirhynchus platorynchus) to describe range-wide growth characteristics and developed a model to estimate ages. Data were solicited throughout much of the current distribution of shovelnose sturgeon, specifically from the mainstem Missouri and Mississippi rivers and their tributaries. Shovelnose sturgeon exhibited variable growth among locations; however, adult fish exhibited almost no growth after they reached a particular size, presumably the size at sexual maturity. Shovelnose sturgeon from the Mississippi River basin attained greater maximum sizes and ages compared with the Missouri River basin. However, two populations from the Mississippi River that received high exploitation from commercial harvest had truncated age distributions with smaller asymptotic lengths. Lower Missouri River populations were characteristic of exploited populations (i.e., smaller fish and reduced longevity), presumably a result of anthropogenic effects. Wide discrepancies in maximum age and size suggest shovelnose sturgeon are capable of displaying phenotypic plasticity in response to exploitation or environmental influences. Determining metapopulation dynamics is a priority because it is unknown how population connectivity may influence dynamic rate functions and persistence of large-river fishes. Identifying potential source-sink connections in terms of population dynamics may provide a template for direction of future restoration and recovery efforts. Nous avons utilise des donnees de marquage-recapture d'esturgeons scaphirhynques (Scaphirhynchusplatorynchus) pour en decrire les caracteristiques de croissance sur l'ensemble de leur aire de repartition et elaborer un modele pour estimer les ages. Des donnees ont ete sollicitees dans la majeure partie de l'aire de repartition actuelle de l'espece, plus precisement des bras principaux de la riviere Missouri et du fleuve Mississippi et leurs affluents. Si la croissance des esturgeons scaphirhynques varie selon la localite, les poissons adultes ne presentent presque aucune croissance apres avoir atteint une taille donnee, vraisemblablement leur taille a maturite sexuelle. Les esturgeons scaphirhynques du bassin du Mississippi atteignent des tailles et des ages maximums superieurs a ceux du bassin de la riviere Missouri. Cependant, deux populations du Mississippi faisant l'objet d'une forte exploitation commerciale presentent des distributions d'ages tronquees et des longueurs asymptotiques plus faibles. Les populations du cours inferieur de la riviere Missouri sont caracteristiques des populations exploitees (c.-a-d. poissons plus petits de longevite reduite), vraisemblablement le resultat d'effets d'origine humaine. De grandes divergences sur le plan de l'age et de la taille maximums donnent a penser que les esturgeons scaphirhynques peuvent faire preuve de plasticite phenotypique en reaction a l'exploitation ou a des influences environnementales. La determination de la dynamique des metapopulations constitue une priorite puisque l'influence de la connectivite des populations sur les fonctions de taux dynamiques et la persistance des poissons de grands cours d'eau demeure inconnue. La determination d'eventuelles connexions source-puits en terme de dynamique des populations pourrait permettre d'orienter les efforts futurs de restauration et de retablissement. [Traduit par la Redaction], Introduction Determining growth is commonly assessed throughout an individual fish's life by back-calculating body length from annuli on calcified structures (e.g., scales, otoliths, fin ray or spine sections, etc.). Back-calculation [...]

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. Les especes longevives de milieux marins et d'eau douce ont connu des baisses d'abondance associees a des effets anthropiques tels que la surexploitation, la construction de barrages et la modification des habitats. La comprehension de la structure par age et de la dynamique associee determinee a partir de ces donnees pour les especes longevives est essentielle tant pour la perseverance des especes en peril que pour le maintien des especes exploitees. Nous avons utilise le scaphirhynque blanc (Scaphirhynchus albus) pour evaluer l'efficacite de donnees de marquage-recapture pour des poissons d'age connu (ages de 1 a 7 ans) eleves en aleviniere pour la verification des estimations de l'age et du taux de croissance obtenues a partir de coupes de rayon de nageoire pectorale. L'exactitude des estimations de l'age pour les poissons d'age connu etait de 13 %, alors que 72 % des estimations differaient de moins de 2 ans de l'age reel. Il y avait une difference significative entre la croissance annuelle estimee (par retrocalcul) et la croissance obtenue a partir d'observations sur des scaphirhynques blancs marques. L'age de scaphirhynques blancs de toute taille a ete estime en utilisant des parametres tires de donnees de marquage-recapture, et la relation predite de la longueur selon l'age etait semblable aux observations pour des individus d'age connu. Dans les cas ou la determination de l'age pour tous les ages d'interet ne peut etre verifiee, l'approche de marquage-recapture semble etre une solution valable pour examiner la croissance et s'annonce prometteuse comme outil pour estimer les ages chez les especes longevives dont les structures calcifiees sont difficiles a dechiffrer. [Traduit par la Redaction], Introduction Long-lived fish species (>20 years) pose a unique set of challenges for assessment and monitoring, as population-level responses may take years to be realized. In marine fisheries, long-lived species [...]

Summary: The recovery criterion for pallid sturgeon Scaphirhynchus albus consists of attaining a self‐sustaining genetically diverse population for two generations. The suppressed pallid sturgeon population is theorized as a potential factor limiting recovery; therefore, the Pallid Sturgeon Conservation and Augmentation Program (PSCAP) was implemented to proliferate the overall population. The pallid sturgeon population has been quantified in the lower basin of the Missouri River (Gavins Point Dam [rkm 1,305.2] to the confluence of the Missouri and Mississippi rivers [rkm 0.0]), but previous population estimates have only covered less than ten percent of the lower basin. Therefore, the objectives of this study were to quantify the annual pallid sturgeon population (2015–2017) in a novel, unquantified 30.1 rkm reach of the lower Missouri River basin and compare these results to previously published population estimates in the lower Missouri River basin. The study area included a six‐bend reach in the upper channelized Missouri River, approximately 226.3 rkm below the last main‐stem dam. Population estimates (Nsp) for the "super‐population" of pallid sturgeon within the 30.1 rkm study area varied from 593 (95% CI 471–716) in 2015 to 471 (373–569) in 2016 and 608 (482–734) in 2017. The population estimates (fish/rkm ± SE) ranged from 15.6 ± 1.0 to 20.2 ± 1.3 fish/rkm. This study aligned with a previously published estimate in the same proximal reach but was two or three times higher compared to an estimate reported from approximately 500 rkm downstream. Understanding the temporal and spatial variations of the pallid sturgeon population is critical as recovery efforts continue, especially to seed input parameters into population prediction models that provide management guidance. [ABSTRACT FROM AUTHOR]

Blue Sucker Cycleptus elongatus are a large-bodied, benthic fish that are considered an indicator species for riverine health. A combination of historic commercial fishing and anthropogenic modifications to riverine habitat led to blue suckers being listed as a candidate species for the federal threatened or endangered species list in 1993. However, they were never designated a federally protected species. Locally, Blue Suckers are currently listed as a Nebraska Natural Legacy Project's Tier 1 species but population changes and trends have not been quantified. Therefore, the objective of this paper was to evaluate the current population status of Blue Sucker in the Missouri River along Nebraska's border. Over 12,000 Blue Suckers were sampled in Nebraska from 2003 to 2012 as part of a targeted effort to characterize the benthic fish community in the Missouri River. Blue Suckers were rarely sampled upstream of Gavins Point Dam. Sampling results from this reach indicate this remnant population is comprised of mostly large adults with very limited reproduction. Capture frequency increased downstream of Gavins Point Dam with adequate reproduction and recruitment to sustain the population in these reaches. Gill net catch consisted of 14% Blue Suckers in the unchannelized reach downstream of Gavins Point and 23% of the benthic fish community in the channelized reach upstream of the Platte River. Age-0 Blue Suckers were most frequently detected in 2011 during the extreme flooding conditions but were also detected in higher abundance in 2006 when the river remained in its channel. The overall population downstream of Gavins Point Dam appears stable or perhaps slightly increasing. Blue Suckers, as with most native fish populations, were negatively affected when the Missouri River was highly modified through dam construction and channelization. However, reproduction and recruitment is occurring and Blue Sucker are not as imperiled as Pallid Sturgeon Scaphirhynchus albus or the native Macrhybopsis species. [ABSTRACT FROM AUTHOR]

The Shovelnose Sturgeon Scaphirhynchus platorynchus remains the most abundant riverine sturgeon species in North American despite the anthropogenic modifications that have occurred throughout their historic range; however, their populations have declined throughout Nebraska since the construction of Fort Randall and Gavins Point Dams. Therefore, the objective of this study was to present the current status of Shovelnose Sturgeon in the Missouri River along Nebraska's border. Data was acquired from 2003 to 2012 from all reaches of the Missouri River along Nebraska's eastern border. Catch rates of Shovelnose Sturgeon increased in a downstream trend and were highest in the reach below the Missouri and Platte River confluence. Based on gill net samples which collected the majority (39%) of Shovelnose Sturgeon, annual catch per unit efforts indicate a declining population above Gavins Point Dam and a stable population below in the open Missouri River. The length frequency distributions of Shovelnose Sturgeon collected were similar across all reaches with the exception of those captured between Fort Randall and the headwaters of Lewis and Clark Lake which were significantly larger than fish captured below the Platte River confluence. Although no age-0 Shovelnose Sturgeon were captured in the unchannelized reaches, age-0 abundance increased in a downstream trend throughout the channelized reaches. Preferred-sized fish (510-640 mm, N = 53,741) were the most common size category of Shovelnose Sturgeon captured throughout all reaches and across all years followed by quality-sized (380-510 mm, N = 12,089) and memorablesized (640-810 mm, N = 4,569) fish. Our data concludes the overall population of Shovelnose Sturgeon above Gavins Point Dam appears to be slightly declining while the population in the open, lower river appears to be stable. [ABSTRACT FROM AUTHOR]

Anthropogenic alterations to the Missouri River have placed the Pallid Sturgeon (Scaphirhynchus albus) population in jeopardy and contributed to their listing as an endangered species. Pallid sturgeon were always less common than the sympatric Shovelnose Sturgeon (S. platorynchus); however, Pallid Sturgeon seemed to be more affected by river alterations as the river sturgeon ratio has become more skewed towards Shovelnose Sturgeon. Shortly after listing, population augmentation with hatchery produced Pallid Sturgeon began to supplement the diminishing wild population. Therefore, the objective of this study was to present the current population status of the Pallid Sturgeon in the Missouri River along Nebraska's border. Moving upstream along Nebraska's eastern border the population of wild Pallid Sturgeon declines and appears very minimal to non-existent upstream of Gavins Point Dam. The wild Pallid Sturgeon population below Gavins Point Dam appears unchanged over the past decade. Hatchery supplementation has stocked almost 12,000 hatchery-reared Pallid Sturgeon above Gavins Point Dam and over 135,000 below, these hatchery-reared fish are surviving and contributing to the overall population throughout all reaches as the capture frequency has increased annually. Currently, the Pallid Sturgeon population consists primarily of stock (66%) and quality- sized (22%) fish, most of which are of hatchery origin. Mean relative condition of quality and preferred-size Pallid Sturgeon varied spatially and temporally. As the Pallid Sturgeon population increases several population recruitment obstacles still exist. Until the bottleneck preventing natural recruitment is lessened, continued listing of the Pallid Sturgeon as an endangered species is critical to drive river management and restoration efforts which are likely to influence species recovery. [ABSTRACT FROM AUTHOR]

Lake Sturgeon (Acipenser fulvescens) occurrences in the Missouri River along Nebraska's eastern border are historically sporadic and rare. Presently, the wild Lake Sturgeon population in this river reach may be extirpated. A Recovery Program initiated by the Missouri Department of Conservation (MDC) has stocked almost 150,000 hatchery-reared Lake Sturgeon into the lower Missouri River at several sites in Missouri. As a result, the number of Lake Sturgeon collected has increased. Since monitoring began in 2003, no Lake Sturgeon have been collected above Gavins Point Dam while 40 fish were collected downstream of Gavins Point Dam. The majority of captures occurred in the lower channelized reach downstream of the confluence of the Platte and Missouri rivers. All fish collected are assumed to be progeny of MDC's Recovery Program as either they were hatchery marked or their size (mean fork length = 764 mm, range = 602-997 mm) correlated with the expected growth rates. At present, their rarity warrants continued listing as a state threated species. [ABSTRACT FROM AUTHOR]