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sturgeon has been rapidly improving during the past 5 years. Even basic parameters such as the <br />microhabitat characteristics of spawning locations, substrate preference, water temperature, or time of <br />year are now beginning to be documented. Spawning occurs between March through July depending <br />on location (Forbes and Richardson 1905, Gilbraith et al. 1988;). Keenlyne and Jenkins (1993) <br />estimate that spawning probably begins in March in the lower Mississippi and Atchafalaya Rivers; in <br />late April or early May in the lower Missouri and middle Mississippi Rivers; and in late May or early <br />June in the upper Missouri River. Sexually mature pallid sturgeon have been observed in the <br />Yellowstone River in western North Dakota during late May and early June when water temperatures <br />ranged from 60 -65T (15.5--18.5-C) (Steve Krentz, USFWS, pers comm.). Sandvol (USFWS, <br />pers. comm., 1992) observed a male pallid sturgeon captured from the Missouri River near Williston, <br />ND, running milt in late May 1991. <br />While no spawning beds have been located, Bramblett (1996) described probable spawning areas in <br />the Yellowstone River from about river km 6 to river km 14. Breder and Rosen (1966) report that as a <br />group, sturgeon exhibit uniform spawning behavior; and thus, such information can be used to make <br />inferences about pallid sturgeon behavior. All sturgeon species spawn in the spring or early summer, <br />are multiple spawners, and release their eggs at intervals. Spawning behavior was observed in 1998 <br />during propagation attempts at Garrison Dam National Fish Hatchery. Following the luteinizing <br />hormone injection, spawning behavior was observed between sexually mature male and female pallid <br />sturgeon within 20 -ft (6.1 m) circular tanks (Rob Holm, USFWS, pers comm.). In the wild, the <br />adhesive eggs are released in deep channels or rapids and are left unattended (Galbraith et al. 1988). <br />The larvae of Acipenserids are generally pelagic, becoming buoyant or active immediately after hatching <br />(Moyle and Cech 1982). Although the behavior of young pallid sturgeon is poorly understood, recent <br />work by Kynard et al. (1998a) indicates that a downstream migration period for larval pallid sturgeon <br />begins day -0 at hatching and continues up to day -13, with a decline after day -8. With this information <br />it has been possible to use water velocities to roughly estimate that larval pallid sturgeon may drift in the <br />water column for a distance of 40 to over 400 mi (64 -643 km) (Steve Krentz, USFWS, pers. comm.). <br />Females collected in June and July in the upper end of Lake Sharpe, a reservoir on the Missouri River <br />in South Dakota, contained mature ova and presumably were ready to spawn. However, during 10 <br />years of sampling for young -of -the -year fish in Lake Sharpe (Kallemeyn 1983) or in the 17 years since <br />then, no evidence of successful reproduction has been found. <br />Kallemeyn (1983) reported that pallid sturgeon males reach sexual maturity at 21 -23 in (53.3 -58.4 <br />cm), however, size and age of females at sexual maturity were unknown at that time. Conte et al. <br />(1988) indicated that females of most sturgeon in North America do not mature until at least age 7 and <br />typically require several years for eggs to mature between spawnings. The age of sexual maturity and <br />intervals between spawning were estimated for nine pallid sturgeon by recording what were interpreted <br />to be spawning events from pectoral fn ray cross sections. Sexual maturity for males was estimated to <br />be 7 to 9 years, with 2 to 3 year intervals between spawning years. Females were estimated to reach <br />sexual maturity in 15 to 20 years, with 3 to 10 year intervals between spawning years ( Keenlyne and <br />100 Status Range Wide -PS <br />