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into July, corresponds with the historic period of increased runoff, which also has been known to trigger <br />spawning of other ancient big -river fish such as paddlefish (Russell 1986) and shovehlose sturgeon <br />(Berg 1981). Gardner (1995a) radio - tracked 14 pallid sturgeon in the upper Missouri River during a <br />low water year and a near normal water year. He found that adult pallid sturgeon moved an average of <br />3.2, 12.9, and 17.6 mi (5.2, 20.8, and 28.3 km) further upriver during May, June, and July in the <br />normal run -off year compared to the low run -off year. These upriver movements are associated with <br />spawning runs and reflect the influence of the hydrograph on pallid sturgeon. <br />Shovelnose sturgeon spawning occurs in the Tongue River, a Yellowstone River tributary, from early <br />June until mid -July (Elser et al. 1977). Female pallid sturgeon collected in June and July in Lake <br />Sharpe contained mature ova and presumably were ready to spawn (Kallemeyn 1983). Krentz <br />(LJSFWS, pers. comm., 1994) observed male pallid sturgeons on the Yellowstone River in Montana <br />running milt during early June of 1993 and 1994. Sandvol (USFWS, pers. comm., 1992) observed a <br />male pallid sturgeon captured from the Missouri River near Williston, ND, running milt in late May <br />1991. Keenlyne and Jenkins (1993) estimated pallid sturgeon spawn in late April or early May in the <br />lower Missouri and middle Mississippi Rivers, and in late May or early June in the upper Missouri <br />River. Although sturgeon have been found that appeared ready to spawn, only two records of larval <br />or young sturgeon have been documented in recent years. Without the increased river flows in June and <br />July, combined with the necessary water temperatures (i.e., >60• F or 15.6• C) during that period, the <br />spawning cues for pallid sturgeon probably are no longer present in some upper basin main stem river <br />reaches under existing main stem dam operations. <br />Conditions may be somewhat better in the lower river. The larval pallid sturgeon collected in Missouri <br />in 1999 suggests a spawning event later than June. Those fish were estimated to be 2 to 3 weeks old <br />(Darrel Snyder, Colorado State University, pers. comm.), beyond the passive drift stage, and able to <br />actively seek out preferred habitat. That indicates that somewhere suitable spawning conditions did <br />occur in 1999 in the lower river when the necessary hydraulic and spatial/temporal habitat conditions <br />coexisted. Nevertheless, in most years the current unnaturally high summer and fall operational flows in <br />the lower river leave few areas suitable for young -of -the -year fish refugia and nursery, reducing <br />potential recruitment into the pallid population. <br />In addition to seasonal shifts in flow patterns, main stem dams operating for daily hydropower needs <br />cause daily water - levels fluctuations in tailwater areas by as much as 6.5 to 10 ft (2 -3 m). Those <br />fluctuations and associated increases in water velocity can disrupt the macroinvertebrate community and <br />larval fish rearing areas for many miles downstream of the dams by alternately flooding and dewatering <br />habitats. Modde and Schmulbach (1973) observed that factors affecting shovelnose sturgeon prey <br />availability within the unchannelized Missouri River include temperature, seasonal recruitment, and <br />changes in density influenced by the timing and discharge rates from Gavins Point Dam. They <br />hypothesized that the reduction in numbers of shovelnose sturgeon may be due to reduced availability of <br />prey species caused by high discharges from Gavins Point Dam. <br />218 Effects - MR - PS <br />