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Sturgeon species (Acipenseridae) around the world have undergone substantial population declines over the past century due to a suite of anthropogenic actions and overharvest. Shovelnose sturgeon are the smallest and most abundant sturgeon species in North America and still support commercial and recreational fisheries despite notable declines in abundance and population structure throughout much of their range. The Rock River, located in Northwestern Illinois, USA, has recently attracted angler attention in response to numerous state record shovelnose sturgeon captured via recreational angling (unregulated recreational fishery), thus prompting the need to understand the size structure and demographics of this largely undescribed population to inform management actions. This study was the first to describe relative condition and size distributions of shovelnose sturgeon in the Rock River, Illinois. A total of 1324 unique shovelnose sturgeon were captured between Fall of 2022 and Winter 2024‐2025, with 22% of captured fish meeting or exceeding trophy size class requirements (≥ 810 mm). Shovelnose sturgeon in the Rock River can reach larger body sizes (length and weight) than other regional systems. The Rock River supports the highest proportion of trophy class shovelnose sturgeon in the world. Although no commercial exploitation occurs, recreational angling is currently unregulated, and this population may be vulnerable to substantial shifts in population structure that may warrant management action. Future research seeks to gain a better understanding of population dynamics and develop robust long‐term monitoring protocols to inform data‐driven management.

The pallid sturgeon Scaphirhynchus albus, a large, long‐lived fish endemic to the Missouri and Mississippi River Basins, was listed as a federally endangered species in 1990 due to population declines driven by profound anthropogenic habitat alterations, including river fragmentation by dams and channelization. In contrast, its congener, the shovelnose sturgeon Scaphirhynchus platorynchus, remains common in large rivers and their tributaries, such as the Des Moines River. Historically, the pallid sturgeon’s range in Iowa has been limited to the Missouri River along the state’s western border. Recovery efforts, as outlined in the National Pallid Sturgeon Recovery Plan, have emphasized habitat restoration and conservation stocking to prevent extirpation and to support natural recruitment. Here, we document the first verified records of wild (nonstocked) pallid sturgeon in the Des Moines River, Iowa. This represents a potential expansion of the species’ known contemporary range and occurs within a tributary not previously identified as occupied habitat. This finding underscores the potential for stocked or wild individuals to disperse into novel river systems where previously undocumented habitat may be available. The finding has immediate conservation implications under the Endangered Species Act, prompting a reassessment of the Des Moines River’s management strategies and necessitating enhanced, targeted sampling efforts. It also raises concerns under the Act’s Similarity of Appearance clause, which governs the legal commercial take of shovelnose sturgeon in the pooled reach of the Upper Mississippi River downstream of the Des Moines River confluence, a potential migration corridor. The presence of pallid sturgeon in the Des Moines River demonstrates that even highly altered river systems can provide essential habitat, such as suitable spawning substrate, needed to support their life cycle, particularly when stream flow is managed to approximate natural hydrologic patterns.

Critical swimming speeds of sturgeon are presumably lower in vertically uniform, rectilinear flow than in heterogeneous boundary-layer flow. Movement in rectilinear flow of the water column necessitates frequent high-energy free-swimming, while movement in boundary-layers near the bottom of the river permits a variety of lower energy behaviours, and presumably, negotiation of greater mid-column water velocities. Comparative studies of sturgeon swimming performance in rectilinear and boundary layer flows, however, are lacking. Using a 1200-l laboratory swim tunnel, swimming performance was measured for 12 adult shovelnose sturgeon (Scaphirhynchus platorynchus), 494-705mm standard length. Tests were conducted at 20-25 degree C in rectilinear (N=4) and boundary-layer flows (N=8). Fifteen minute critical swimming speeds ranged from 89.3 to 112.6cms-1 in rectilinear flow, 129.5-172.1cms-1 in boundary-layer flow. Higher critical swimming speeds observed in boundary-layer flows was a combination of behavioural adaptations (body appression to flat, horizontal substrate) and availability of a low velocity refugium (water velocities at bottom of tank 21-65cms-1 slower than those in mid and upper levels of tank). Results support the idea that sturgeon exploit boundary-layers to effectively move or hold position in fast-flowing rivers. Data may be applied to man-made river structures to facilitate fish passage and to reduce risk of sturgeon entrainment.

Sicklefin (Macrhybopsis meeki) and sturgeon chub (M. gelida) historically occurred throughout the Missouri River (MR), in some tributaries, and Mississippi River downstream of the MR. They have been species of U.S. state-level conservation concern and U.S. Endangered Species Act listing candidates since the 1990s. We applied analytical approaches from occupancy modeling to correlation to monitoring data spanning 23 years to assess relationships between occupancy and time, space, environmental factors, habitat, and other species. Sicklefin chub occupancy appeared higher in the early to mid-2000s and mid-to-late 2010s. A potential decline in occupancy occurred for sturgeon chub in the mid-to-late 2010s. Spatially, chub occupancy was depressed for 159 to 438 km downstream of MR dams. Among macrohabitats, inside bends had relatively high occupancy for both species; secondary connected channels had relatively high values for sturgeon chub. Co-occurrence was likely between sicklefin and sturgeon chub and between chubs and shovelnose sturgeon (Scaphirhybchus platorybchus) and channel catfish (Ictalurus punctatus). The observed co-occurrence of chubs and pallid sturgeon (Scaphirhynchus albus; PS) was potentially higher than expected for adult PS. For juvenile PS, co-occurrence was lower than expected in the Lower MR and potentially higher than expected in the Upper MR, warranting future research. Results from this research suggest management for the improvement of sicklefin and sturgeon chub populations may benefit other MR fish populations.

Summary 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.

Summary The hypotheses of this study were (i) that shovelnose sturgeon would make upstream movements to spawn, (ii) movement of spawning fish would be greater in a year with higher discharge, and (iii) that spawning fish would have greater movements than reproductively inactive fish. Shovelnose sturgeon Scaphirhynchus platorynchus (Rafinesque, 1820) in five reproductive categories (e.g. males, confirmed spawning females, potentially spawning females, atretic females, and reproductively inactive females) were tracked in 2008 and 2009. All reproductive categories, except reproductively inactive females, exhibited large‐scale movements and had omnidirectional movements. No differences in movement rates were observed in confirmed spawning females between years despite a 45% higher peak discharge in 2008 (839 m3 s−1) than in 2009 (578 m3 s−1). A peak discharge was obtained at a faster rate in 2008 (165 m3 s−1 day−1) than in 2009 (39 m3 s−1 day−1), and high discharge was of greater duration in 2008. Reproductively inactive females did not exhibit large‐scale movements and their movement rate differed from other reproductive categories. Shovelnose sturgeon spawned in both years, despite highly varying hydrographs between years.

Summary The range of Shovelnose Sturgeon (SVS) Scaphirhynchus platorynchus in the great rivers of central North America has contracted, but most remaining populations are considered stable, likely due to a combination of successful harvest regulations and longitudinal continuity of many river reaches, despite damming in upper reaches. The evolutionary relationships of SVS relative to sister taxa is still a matter of debate. Genetic diversity varies across the range, with substantial haplotype overlap among SVS and its congeners. Shovelnose Sturgeon mature early at 5–7 years, and spawn every 2–3 years. Some individuals may spawn in fall. Whether this species migrates is debatable, but individuals move long distances with larvae dispersing greater than 250 km, and adults moving >1900 km. Shovelnose Sturgeon appear to complete all aspects of their life cycle in the main channel of rivers, with sand and associated dunes playing an important role in station holding even at high flows. The greatest threats to this species include river temperatures exceeding 26°C that may impair growth and survival of young life stages, dams that impair movement during spring flooding, loss of critical mid‐channel island habitats which may be important nursery areas, and increases in harvest pressure for the caviar trade. Given the broad distribution of this species across the jurisdiction of multiple states in the US, a species‐wide conservation plan should be in place to ensure that SVS populations remain stable or increase.

Uncertainty in risks posed by emerging stressors such as synthetic hormones impedes conservation efforts for threatened vertebrate populations. Synthetic hormones often induce sex‐biased perturbations in exposed animals by disrupting gonad development and early life‐history stage transitions, potentially diminishing per capita reproductive output of depleted populations and, in turn, being manifest as Allee effects. We use a spatially explicit biophysical model to evaluate how sex‐biased perturbation in life‐history traits of individuals (maternal investment in egg production and male‐skewed sex allocation in offspring) modulates density feedback control of year‐class strength and recovery trajectories of a long‐lived, migratory fish—shovelnose sturgeon (Scaphirhynchus platorynchus)—under spatially and temporally dynamic synthetic androgen exposure and habitat conditions. Simulations show that reduced efficiency of maternal investment in gonad development prolonged maturation time, increased the probability of skipped spawning, and, in turn, shrunk spawner abundance, weakening year‐class strength. However, positive density feedback disappeared (no Allee effect) once the exposure ceased. By contrast, responses to the demographic perturbation manifested as strong positive density feedback; an abrupt shift in year‐class strength and spawner abundance followed after more than two decades owing to persistent negative population growth (a strong Allee effect), reaching an alternative state without any sign of recovery. When combined with the energetic perturbation, positive density feedback of the demographic perturbation was dampened as extended maturation time reduced the frequency of producing male‐biased offspring, allowing the population to maintain positive growth rate (a weak Allee effect) and gradually recover. The emergent patterns in long‐term population projections illustrate that sex‐biased perturbation in life‐history traits can interactively regulate the strength of density feedback in depleted populations such as Scaphirhynchus sturgeon to further diminish reproductive capacity and abundance, posing increasingly greater conservation challenges in chemically altered riverscapes.

Background. White sturgeon iridovirus (WSIV) is one of the most serious threats for sturgeon aquaculture as the mortality in juvenile individuals can reach 95%. At the turn of the century WSIV was reported among hatchery-raised white sturgeon, Acipenser transmontanus Richardson, 1836, in North America, Russian sturgeon , Acipenser gueldenstaedtii Brandt et Ratzeburg, 1833, in northern Europe but also pallid sturgeon, Scaphirhynchus albus (Forbes et Richardson, 1905) and shovelnose sturgeon, Scaphirhynchus platorynchus (Rafinesque, 1820) in North and South Dakota. The clinical signs of infection include cessation of feeding and edematous and pale gills. Those pathological changes lead to respiratory problems of the juveniles and deterioration of their overall condition. Rapid detection of pathogen particles under aquaculture conditions is crucial, therefore the principal aim of this study was to establish a molecular method for rapid and effective detection of the WSIV. This is the first study thoroughly comparing WSIV detection methods in sturgeons cultured in Poland, Germany, and Italy. Material and methods. A total of 244 samples were collected from 82 sturgeons representing six species: beluga, Huso huso (Linnaeus, 1758); sterlet, Acipenser ruthenus Linnaeus, 1758; Siberian sturgeon, Acipenser baerii Brandt, 1869; Russian sturgeon, A. gueldenstaedtii; Atlantic sturgeon, Acipenser oxyrinchus Mitchill, 1815; and European sea sturgeon, Acipenser sturio Linnaeus, 1758, as well as five sturgeon hybrids: Siberian x Russian, Adriatic (Acipenser naccarii Bonaparte, 1836) x Siberian, Adriatic x beluga, Siberian x sterlet, and beluga x sterlet. The samples were screened for the WSIV using conventional PCR, real-time PCR, and in situ hybridization (ISH) methods. Results. In total, positive results were obtained in 231 (94.67%) out of 244 analysed samples, except for H. huso where DNA of WSIV was not identified. DNA of WSIV was most frequently detected in the kidney (97.92%), intestine (97.50%), skin (94.97%), and gills (93.29%). The most effective method for detecting DNA of WSIV in sturgeons was real-time PCR (92.62% of), PCR (90.98%), and ISH (49.24%). Conclusion. The host range of the WSIV seems to be wider than expected, however, further studies are necessary since no clinical symptoms were observed in sturgeons and their hybrids.