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.U.S.

Summary 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.

Pallid Sturgeon Scaphirhynchus albus are endemic to the Missouri and Mississippi river basins and are rare throughout their range. The species was listed as federally endangered with little to no evidence of natural recruitment. Since population augmentation was initiated as a recovery objective in the early 1990s, thousands of hatchery-origin Pallid Sturgeon have been stocked in the lower Missouri River (Gavins Point Dam [river kilometer 1,305.1] to the confluence of the Mississippi River [river kilometer 0.0]). Efforts to discriminate natural reproduction and recruitment of wild-origin Pallid Sturgeon from hatchery-origin fish has been hampered by tag loss in hatchery-origin sturgeon, inconsistent documentation of hatchery parental crosses, and the failure to collect tissue samples for genotyping all broodstock. However, the recent reconstruction of missing parental genotypes from known hatchery-origin progeny and from cryopreserved milt made it possible to examine Pallid Sturgeon recruitment. Therefore, our objectives were to 1) determine the likelihood that unmarked Pallid Sturgeon captured from the lower Missouri River were the result of natural recruitment and 2) examine the length distribution of wild- and hatchery-origin fish to determine if a difference exists by origin and examine the life-stage distribution. Genetic analysis showed that from 2003 to 2015, 358 “presumptive wild-origin” Pallid Sturgeon were captured in the lower Missouri River and the comparison between the length distributions of wild- and hatchery-origin fish did not provide any additional clarification into potential wild-origin fish. Low recruitment may be due to a small breeding population, high mortality of early life stages, hybridization with Shovelnose Sturgeon Scaphirhynchus platorynchus, or transport of drifting free embryos or larvae into inhospitable habitats. Determining what factors are limiting recruitment is the important next step for the recovery of Pallid Sturgeon in the lower Missouri River.

North America has lost >95% of its native tallgrass prairie due to land conversion, making prairie streams one of the most endangered ecosystems. Research on the basic ecosystem characteristics of the remaining natural prairie streams will inform conservation and management. We examined the structure and function of headwater streams draining tallgrass prairie tracts at Osage Prairie in Missouri and the Konza Prairie Biological Station in Kansas and compared those values with literature values for streams draining agricultural watersheds in the region. We quantified physicochemical and biological characteristics for 2 yr. Streams at Osage and Konza were characterized by low nutrients and low suspended sediments (substantially lower than impacted sites in the region), slight heterotrophic status, and high temporal variability. Suspended sediments and nutrient concentrations were generally low in all prairie streams, but storms increased concentrations of both by 3- to 12-fold. Spring prescribed burns were followed by a slight increase in chlorophyll and decreased nutrients, potentially due to greater light availability. Benthic macroinvertebrate communities at Osage showed seasonal patterns that were probably linked to variable hydrology. We found nine amphibian species using the Osage streams as habitat or breeding sites, but little usage at Konza was probably due to dry conditions and low discharge. Our study indicates that two remnant tallgrass prairie streams along a longitudinal gradient are fairly similar in terms of physicochemical features and have good water quality relative to agricultural watersheds but can differ considerably in macroinvertebrate and amphibian abundance.

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.U.S.