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The diet composition was quantified of year-0 Scaphirhynchus sturgeons during sampling years (2004-2008) from the Middle Mississippi River to evaluate trends in diet. River stage height varied among years and seasons. Water temperature differed among seasons but did not differ among years. The presence of empty stomachs was evident across years, seasons, and size classes of sturgeon. The overall Multivariate Analysis of Variance for frequency of occurrence was significant, suggesting that macroinvertebrate taxa (e.g. Ephemeroptera, Diptera pupae, Chironomidae, ' Other') differed among size classes of sturgeon, but not seasons or years. Furthermore, Tukey's pairwise comparisons indicated Ephemeroptera frequency of occurrence differed between medium and large size classes; Diptera pupae differed between small and medium size classes and small and large size classes; Chironomidae differed between small and large size classes and medium and large size classes; the macroinvertebrate taxa category ' Other' differed between small and large size classes. Ultimately, because of the link between diet and growth of year-0 Scaphirhynchus sturgeon, the early life history may affect eventual recruitment to adult stages. [ABSTRACT FROM AUTHOR]

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Varying degrees of connectivity between side channels and the main river channel are vital for sustainable ecological processes and functions for both aquatic and terrestrial communities. Within the Mississippi River, restoring side channel functional diversity is a top priority for many natural resource agencies. Buffalo Chute, located at river kilometer 41, is one of the several side channels, island complexes that becomes isolated from the main channel during low river stages leading to thermal and chemical stratifications and anoxic conditions. The purpose of this study was to better understand the impacts of side-channel isolation in the middle Mississippi River (MMR) by measuring fish community and water quality characteristics within an isolated waterbody. Therefore, we selected Buffalo Chute a representative side channel of the MMR to document water quality and fish community characteristics. Water quality measurements were summarized for the 2-year study. Thermal and chemical stratifications coupled with high water temperatures and anoxic conditions were observed in both years during summer. Oxygen reduction potential was lower in summer than winter, which could be attributed to excessive growth of microorganisms and increased biological oxygen demand. Specific conductivity, total phosphorus, total nitrogen, and chlorophyll a were higher in summer compared to winter. Differences in water quality characteristics may have resulted in lower mean fish species richness, diversity, and evenness observed during the following winter. We surveyed 45 sites over 2 years using multiple gears to assess fish assemblage characteristics. The data collected in Buffalo Chute provide some insight into how isolated side channels function during low flow periods. [ABSTRACT FROM AUTHOR]

Several studies have investigated the demographics of shovelnose sturgeon Scaphirhynchus platorynchus and pallid sturgeon S. albus in the Mississippi River through assessment of adult populations; however, comparatively few studies have examined the early life history of these species. Here, we describe a comprehensive 4-year study that examined the effects of water temperature and river stage on the mortality, abundance, hatch timing, and growth rates of age-0 Scaphirhynchus spp. sturgeon in the middle Mississippi River. We trawled island areas every 7-10 d from April to August 2004-2007. We captured 1,256 individuals ranging from 10 to 193 mm total length over the 4-year study. Mean age-0 sturgeon growth rates ranged from 1.42 to 1.50 mm/d over the 4 years; however, growth rates did not differ among years. Individuals hatched over a 25-65-d period, and peak hatch dates were between 10 and 20 May in all years. Moreover, hatch timing possibly coincided with optimum spawning temperatures of 17-20°C and an increase in river stage. Abundance appeared to be regulated by river stage; longer durations of high water were related to higher relative abundance. Furthermore, mortality increased with the number of days on which water temperature exceeded 28°C. Based on these data, management strategies may need to ensure sturgeon hatching success and subsequent survival through optimizing hydrologic and thermal regimes that occur during the early life stage. [ABSTRACT FROM AUTHOR]