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shovelnose sturgeon. All larval Scaphirhynchus spp. that have been collected <br />have been classified as shovelnose sturgeon because of the rarity of pallid <br />sturgeon.) Spawning reportedly occurs between June and August (Forbes and <br />Richardson 1905). Females collected in June and July in Lake Sharpe, a <br />reservoir on the Missouri River in South Dakota, contained mature ova and <br />presumably were ready to spawn. However, there has been no evidence of <br />successful reproduction during 10 years of sampling for young -of- the -year fish <br />in Lake Sharpe (Kallemeyn 1983). <br />Kallemeyn (1983) reported that pallid sturgeon males reach sexual maturity at <br />53.3 -58.4 cm (21 to 23 in), but size and age of females at sexual maturity are <br />unknown. Conte et al. (1988) indicated that females of most sturgeon in North <br />America do not mature until 7 years of age and typically require several years <br />for eggs to mature between spawnings. <br />The age of sexual maturity and intervals between spawning were estimated for <br />nine pallid sturgeon by recording what were interpreted to be spawning events <br />from pectoral fin ray cross sections (L. Jenkins, U.S. Fish & Wildlife <br />Service, pers. comm. 1991). Sexual maturity for males was estimated to be <br />7 to 9 years, with 2- to 3 -year intervals between spawning years. Females <br />were estimated to reach sexual maturity in 15 to 20 years, with 3- to 10 -year <br />intervals between spawning years. Time of sexual maturity and the intervals <br />between spawning years is likely to be influenced by available forage, <br />environmental conditions, and other factors. <br />Keenlyne et al. (1992) estimated fecundity for a female pallid sturgeon taken <br />from the upper Missouri River. The authors found the mass of mature eggs <br />weighed 1,952 g, which represented 11.4 percent of total body weight. Total <br />fecundity was estimated at 170,000 eggs for this female. <br />While there may be differences in the spawning requirements between the pallid <br />sturgeon and shovelnose sturgeon, the shovelnose sturgeon still provides the <br />closest model for determining spawning requirements. Because there is little <br />information available on pallid sturgeon spawning, spawning requirements are <br />extrapolated from what is known regarding shovelnose sturgeon spawning. <br />Shovelnose sturgeon spawn over substrates of rock, rubble, or gravel in the <br />main channel of the Missouri /Mississippi Rivers and major tributaries, or on <br />wing dams in the main stem of larger rivers (Christiansen 1975; Elser et al. <br />1977; Moos 1978; Helms 1974). Shovelnose sturgeon spawning occurs in the <br />unchannelized Missouri River near Vermillion, South Dakota, when water <br />temperatures reach 18 °C to 190C.(64 °F to 66 °F), which can be from late May <br />through June. Spawning was suspected to occur in the relatively swift water <br />in or near the main channel (Moos 1978). Shovelnose sturgeon spawning occurs <br />in the Tongue River, Montana, a Yellowstone River tributary, from early June <br />until mid -July at water temperatures of 16.9 °C to 21.5 °C (61 °F to 70 °F) ( Elser <br />et al. 1977). Initiation of shovelnose sturgeon spawning migrations have been <br />associated with increased flows in June (Berg 1981). <br />Food and Feeding Habits: Carlson et al. (1985) determined composition of food <br />categories, by volume and frequency of occurrence, in the diet of shovelnose <br />sturgeon (n =234), pallid sturgeon (n =9), and presumed hybrids (n =9). Aquatic <br />