Water temperature plays a key role in determining the persistence of shovelnose sturgeon Scaphirhynchus platorynchus in the wild and is a primary factor affecting growth both in the hatchery and in natural waters. We exposed juvenile shovelnose sturgeon to temperatures from 88C to 308C for 87 d to determine the effect of temperature on growth, condition, feed efficiency, and survival. Growth occurred at temperatures from 128C to 308C; the optimal temperature predicted by regression analysis was 22.48C, and the minimum temperature needed for growth was greater than 10.08C. The maximum feed efficiency predicted by regression analysis was 24.5% at 21.78C, and condition factor was highest in the 188C treatment. Mortality was significantly higher at 288C and 308C than at lower temperatures but less than 10% across the thermal regimes tested and 0% at 14-188C. Mortality was observed at and below 128C, suggesting that extended periods of low temperature may deplete energy reserves and lead to higher mortality. Rearing juvenile shovelnose sturgeon at temperatures above 248C reduced the growth rate and feed efficiency and increased mortality. Temperatures in the range 18-208C appeared to maximize the combination of condition, growth, and feed efficiency while not increasing thermal stress. This study corroborates field studies suggesting that altered temperature regimes in the upper Missouri River reduce the growth of shovelnose sturgeon. This information may help protect the thermal habitat critical to the species and guide restoration efforts by delineating temperature regime standards for regulated rivers and those affected by hydroelectric facilities and suggesting new criteria for conservation propagation.

Summary The Pallid Sturgeon is listed as federally endangered under the Endangered Species Act in the United States. When the species was listed in 1990 it was considered extremely rare and was poorly understood. Habitat alteration, commercial harvest, environmental contaminants, and other factors were identified as threats. Today our scientific understanding of the species and its life history requirements have increased greatly as summarized below.

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Downloaded by [University of Saskatchewan Library] at 04:30 04 February 2015Fisheries | www.fisheries.org 7 FEATURE Ampliando el paradigma de manejo de la regulación de ríos: la olvidada zona muerta como obstáculo para la recuperación del esturión pálido La proliferación de presas a nivel global durante el último medio siglo, ha llevado a los ecólogos a tratar de comprender los efectos que tiene la regulación de ríos sobre los grandes peces de agua dulce. Actualmente, gran parte de los esfuerzos dirigidos a mitigar la influencia de las presas en los grandes peces de agua dulce se han enfocado en los efectos observados en la porción inferior de las cuencas y poca atención se le ha dado a los efectos río-arriba. A través de una combinación de observaciones de campo y experimentos de laboratorio, se probó la hipótesis de que las condiciones abióticas río-arriba en las presas son el mecanismo que explica las fallas del reclutamiento del esturión pálido (Scaphirhynchus albus), una icónica especie de agua dulce, de gran tamaño, catalogada como amenazada. Se muestra por vez primera que la anoxia en hábitats río-arriba en los reservorios (i.e., zonas de transición entre ríos y reservorios) es probablemente responsable de las fallas en el reclutamiento del esturión pálido. Las condiciones de anoxia en la zona de transición es función de la reducción de la velocidad de flujo del río y la concentración de material orgánico fino particulado, con un alto contenido de respiración microbiana. Como se predijo, las condiciones del río por encima de la zona de transición fueron óxicas en todos los sitios de muestreo. Los resultados indican que las zonas de transición representan un sumidero para el esturión pálido, Se argumenta que los ecólogos, ingenieros y tomadores de decisiones requieren de ampliar el paradigma de la regulación de ríos, con el objeto de incluir los efectos que tienen las presas tanto río-arriba como río-abajo y, así mismo, mitigar sistemáticamente los ecosistemas afectados en beneficio de los grandes peces de agua dulce, especialmente el esturión pálido.The global proliferation of dams within the last half century has prompted ecologists to understand the effects of regulated rivers on large-river fishes. Currently, much of the effort to mitigate the influence of dams on large-river fishes has been focused on downriver effects, and little attention has been given to upriver effects. Through a combination of field observations and laboratory experiments, we tested the hypothesis that abiotic conditions upriver of the dam are the mechanism for the lack of recruitment in Pallid Sturgeon (Scaphirhynchus albus), an iconic large-river endangered species. Here we show for the first time that anoxic upriver habitat in reservoirs (i.e., the transition zone between the river and reservoir) is responsible for the lack of recruitment in Pallid Sturgeon. The anoxic condition in the transition zone is a function of reduced river velocities and the concentration of fine particulate organic material with high microbial respir...

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 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.

Many lotic fish species use natural patterns of variation in discharge and temperature as spawning cues, and these natural patterns are often altered by river regulation. The effects of spring discharge and water temperature variation on the spawning of shovelnose sturgeon Scaphirhynchus platorynchus have not been well documented. From 2006 through 2009, we had the opportunity to study the effects of experimental discharge levels on shovelnose sturgeon spawning in the lower Marias River, a regulated tributary to the Missouri River in Montana. In 2006, shovelnose sturgeon spawned in the Marias River in conjunction with the ascending, peak (134 m 3 /s) and descending portions of the spring hydrograph and water temperatures from 16 C to 19 C. In 2008, shovelnose sturgeon spawned in conjunction with the peak (118 m 3 /s) and descending portions of the spring hydrograph and during a prolonged period of increased discharge (28-39 m 3 /s), coupled with water temperatures from 11 C to 23 C in the lower Marias River. No evidence of shovelnose sturgeon spawning was documented in the lower Marias River in 2007 or 2009 when discharge remained low (14 and 20 m 3 /s) despite water temperatures suitable and optimal (12 CÀ24 C) for shovelnose sturgeon embryo development. A similar relationship between shovelnose sturgeon spawning and discharge was observed in the Teton River. These data suggest that discharge must reach a threshold level (28 m 3 /s) and should be coupled with water temperatures suitable (12 CÀ24 C) or optimal (16 CÀ20 C) for shovelnose sturgeon embryo development to provide a spawning cue for shovelnose sturgeon in the lower Marias River.

The swimming performance of longnose dace Rhinichthys cataractae, the most widely distributed minnow (Cyprinidae) in North America, was assessed in relation to potential passage barriers. The study estimated passage success, maximum ascent distances and maximum sprint speed in an open-channel flume over a range of water velocities and temperatures (10·7, 15·3 and 19·3° C). Rhinichthys cataractae had high passage success (95%) in a 9·2 m flume section at mean test velocities of 39 and 64 cm s , but success rate dropped to 66% at 78 cm s . Only 20% of fish were able to ascend a 2·7 m section with a mean velocity of 122 cm s . Rhinichthys cataractae actively selected low-velocity pathways located along the bottom and corners of the flume at all test velocities and adopted position-holding behaviour at higher water velocities. Mean volitional sprint speed was 174 cm s when fish volitionally sprinted in areas of high water velocities. Swimming performance generally increased with water temperature and fish length. Based on these results, fishways with mean velocities <64 cm s should allow passage of most R. cataractae. Water velocities >100 cm s within structures should be limited to short distance (<1 m) and structures with velocities ≥158 cm s would probably represent movement barriers. Study results highlighted the advantages of evaluating a multitude of swimming performance metrics in an open-channel flume, which can simulate the hydraulic features of fishways and allow for behavioural observations that can facilitate the design of effective passage structures.