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.