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Micro - Habitat Characteristics - Microhabitat characteristics of pallid sturgeon are just recently <br />being described. Much of the microhabitat research to date is located in significantly altered <br />environments. That research does not necessarily indicate preferred or required habitats; instead it may <br />only indicate which habitats of those presently available are used by the pallid sturgeon. Also, capture <br />locations may have conditions representing seasonal habitat preferences. Hurley (1996) found that <br />pallid sturgeon were selecting downstream island tips although they were not abundant within the study <br />area. <br />Current/Velocity: Findings from a study on the Missouri River in South Dakota indicate that pallid <br />sturgeon most frequently occupy river bottoms where velocity ranges from 0 to 0.73 m/s (Erickson <br />1992). Other studies in Montana found that pallids are most frequently associated with water velocities <br />ranging from 0.46 to 0.96 m/s (Clancey 1990). Bramblett (1996) noted pallid sturgeon occupying <br />bottom velocities ranging from 0.0 to 1.37 m/s. These velocities are commonly found throughout the <br />species' range. <br />Pallid sturgeon collected from the Missouri River above Garrison Reservoir in North Dakota during <br />spring and fall seasons of 1988 to 1991 were found in deep pools at the downstream end of chutes and <br />sandbars, and in the slower currents of near -shore areas. Those areas may have been providing good <br />habitat for energy conservation and feeding ( USFWS 1993). Sheehan et al. (1998a) indicated that <br />there were no shifts in habitat selection and avoidance by middle Mississippi River pallid sturgeon under <br />three different discharge regimes (low, medium and high discharge ranges of 0 - 165 Kcfs, 165 Kcfs to <br />270 Kcfs and >270 Kcfs). Data collected by Constant et al. (1997) support observations that <br />shovelnose sturgeon tolerate lower current velocities than pallid sturgeon (Carlson et al. 1985, Ruelle <br />and Keenlyne 1994, Bramblett 1996). They found that pallid sturgeon catch - per -unit -effort (CPUE) <br />declined following shutdown of the Old River Control Structure and that no pallid sturgeon were <br />collected when current velocity was reduced to zero, although shovelnose sturgeon CPUE was highest <br />at this time. <br />Turbidity- . Pallid sturgeon historically occupied turbid river systems. Turbidity levels where pallid <br />sturgeon have been found in South Dakota range from 31.3 to 137.6 Nephelometric turbidity units <br />(NTU) (Erickson 1992). Pallid sturgeon avoid areas without turbidity and current (Bailey and Cross <br />1954, Erickson 1992). That behavior contributes to the reason why pallid sturgeon are no longer found <br />in the Missouri River reservoirs, and have not expanded into other rivers in the Mississippi drainage, <br />even though access is available (Duffy et al. 1996). <br />Water Depth Pallid sturgeon were frequently found in water depths of 2 to 6 in in South Dakota <br />(Erickson 1992). In Montana, pallid sturgeon were captured from depths between 1.2 to 3.7 in in the <br />summer, but they were captured in deeper waters during winter (Clancey 1990). Other pallid sturgeon <br />collected in the upper Missouri, Yellowstone and Platte Rivers were captured in depths between 1 to <br />7.6 in (Watson and Stewart 1991, USFWS 1993). Bramblett (1996) found pallid sturgeon in depths <br />from 0.6 to 14.5 m. That contrasts with Constant et al. (1997) which found pallid sturgeon at mean <br />Status Range Wide -PS 109 <br />