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Erickson (1992) found pallid sturgeon movement greater during the night while Bramblett (1996) <br />observed greater movements during the day. The primary habitat difference suspected in those findings <br />was turbidity. Erickson (1992) had secchi readings as high as 157 in (400 cm) while Bramblett (1996) <br />averaged 8 in (20 cm) and rarely exceeded 39 in (100 cm). Bramblett (1996) modeled the information <br />from his study and found that predictive depth of pallid sturgeon was greater during the hours following <br />sunrise and suggested that pallid sturgeon may be photophobic. <br />The spawning period for pallid sturgeon, believed to occur from late April into July, historically <br />corresponded with increased flows from runoff, which also has been known to trigger spawning of <br />other ancient big -river fish such as paddlefish (Russell 1986) and shovehiose sturgeon (Berg 1981). <br />Gardner (1995a) radio tracked 14 pallid sturgeon in the upper Missouri River during a low water runoff <br />year and a near - normal year. He found that adult pallid sturgeon moved an average of 3.2, 12.9, and <br />17.6 mi (5.1, 20.7, 28.3 km) further upriver during May, June, and July of the normal runoff year <br />compared to the low runoff year. <br />Both shovelnose sturgeon and paddlefish spawning migrations occur in response to increased flows in <br />June (Berg 1981). Although there is limited information on pallid sturgeon spawning migrations, <br />Bramblett (1996) stated that discharge and photoperiod may be important environmental cues for the <br />timing of movements for both shovelnose and pallid sturgeon. He found a typical pattern of movement <br />for pallid sturgeon was to move upstream into the Yellowstone River and out of the Missouri River in <br />the early spring during increasing discharge and photoperiod; reside in the Yellowstone River during <br />high discharge; and move downstream, back into the Missouri River during late summer. A similar <br />pattern has been observed in the paddlefish population (John Firehammer, University of Idaho, pers. <br />comm.). <br />Erickson (1992) and Bramblett (1996) observed that movement rates of pallid sturgeon were lowest in <br />winter months and a significant positive correlation between water temperatures and movement rate of <br />pallid sturgeon existed. <br />Juvenile pallid sturgeon from Gavins Point NFH in South Dakota were subjected to swimming stamina <br />tests in 1998. Adams et al. (1999) found sustained and prolonged speeds of juvenile pallid sturgeon <br />were comparable to similar sized lake sturgeon; however, pallid sturgeon exhibited a higher capacity <br />for burst swimming. Adult shovelnose sturgeon, a closely related species, were also tested for <br />swimming endurance. Sturgeon were found to swim volitionally at low speeds (5 -30 c /s), but at higher <br />speeds (40 -120 c /s), sturgeon alternated between active swimming and appressing themselves to the <br />bottom of the swimming tunnel (USFWS 1999). This second behavior is enhanced by sturgeon <br />morphology - streamlined body shape, flat rostrum, and large pectoral fins. It allows sturgeon to <br />exploit river bottoms as a refugia from current and maintain position in high velocities. <br />Population Status and Trends <br />Status Range Wide -PS 103 <br />