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Jenkins 1993). Time of sexual maturity and the age intervals between spawning years is likely to be <br />influenced by available forage, environmental conditions and other factors (USFWS 1993), and thus, <br />likely varies to some degree between river reaches. <br />Keenlyne et al. (1992) estimated fecundity for a female pallid sturgeon taken from the upper Missouri <br />River. The authors found the mass of mature eggs weighed 69 oz (1,952 g), which represented 11.4 <br />percent of total body weight. Total fecundity was estimated at 170,000 eggs for this female. Females <br />may take up to 10 years between spawnings depending on the quality and quantity of food available in <br />their natural habitat ( Keenlyne and Jenkins 1993). The food availability is in turn dictated by habitat <br />factors such as flow, water temperatures, substrate, and structure. Therefore, fecundity of a female <br />may vary considerably, with an individual female spawning only a few times during her normal life span <br />(Duffy et al. 1996). <br />Henry and Ruelle (1992) calculated the gonadosomatic index (GSI) and fecundity for one female <br />pallid/shovelnose sturgeon hybrid and three female pallid sturgeon captured on the Mississippi River. <br />The fecundity of the hybrid was estimated at 61,992 eggs. This fish had the highest GSI (23.9) of the <br />other sturgeon measured. The eggs of the pallid sturgeon were not as mature and had GSI's of 7.2, <br />9.0, and 10.5. <br />While subtle differences likely exist in the spawning requirements of the pallid sturgeon and shovelnose W4 <br />sturgeon, the shovelnose sturgeon is believed to provide a good indication of spawning requirements for <br />pallid sturgeon. The two species are reported to hybridize (Carlson et al. 1985). Shovelnose sturgeon <br />spawn over substrates of rock, rubble �r �, avel �„ rhP main-channel of the Missouri/Mississippi Rivers <br />and major tributaries, or on wma dams in the main stem of larger rivers (Helms 1974, Elser et al. 1977, <br />Moos 1978). Spawning was uspecte occur in the relativel swift water in or near the main <br />channel the c annelized Missouri River near Vermillion, South Dakota, when water temperatures <br />ch 64• to 66• F (18• to 19- C), which can be from late May through June (Moos 1978). <br />Shovelnose sturgeon spawning occurs in the Tongue River, Montana, a Yellowstone River tributary, <br />from early June until mid -July at water temperatures of 62.4• to 70.7• F (16.9• to 21.5• C) ( Elser et al. <br />1977). Pallid sturgeon have been spawned on three different occasions at both Gavins Point NFH and <br />Garrison Dam NFH. Water temperatures and egg quality were monitored prior to and during <br />spawning and analysis has shown that the optimum spawning temperature ranged from 60• to 65• F <br />(15.5• to 18.5• C) immediately prior to the spawning (Steve Krentz, USFWS, pers. comm.). <br />Without increased flows in Jun d July, and warmer water temperatures during that period, the cues <br />for pallid sturgeon to spawn probably are no longer present under existing main stem dam operations, <br />throughout much of the Missouri River. <br />Age and Growth - Little is known about age and growth of pallid sturgeon. This is primarily due to <br />lack of sturgeon tissues that allow age determination. Use of the leading ray of the pectoral spine has <br />provided age estimates; however, the Pallid Sturgeon Recovery Team does not support the collection <br />Status Range Wide -PS 101 <br />