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River provide an estimate of between 1,303 to 6,516 pallid sturgeon in this river section (Duffy et al, <br />1996). Those estimates are considered subjective due to the lack of mark/recapture data. <br />In response to obvious declines in pallid sturgeon numbers and the notable lack of recruitment, MDC <br />began an augmentation effort by releasing fingerlings raised at Blind Pony State Fish Hatchery. <br />Approximately 7,000 fingerlings were released in the Missouri and Mississippi Rivers in 1994 and an <br />additional 3,000 fingerlings were released in 1997 (Graham 1997, 1999). Since the release, <br />approximately 127 tagged pallid sturgeon have been reported (Graham, pers. comm. 2000). Most of <br />these fish are being reported below St. Louis likely due to higher numbers of commercial fisherman in <br />the Mississippi River (Graham 1999). <br />Eleven experimental stockings and population augmentation efforts within the six separate recovery <br />priority management areas (USFWS 1993a) have occurred over the last 7 years (Table 11). These <br />efforts have temporarily boosted total population numbers. The effects of mortality and subsequent <br />rates of survival are currently unknown. <br />Field surveys of Scaphirhynchus stocks suggest a relatively high incidence of hybridization between <br />shovelnose sturgeon and pallid sturgeon in the middle Mississippi River (Sheehan 1997a, 1997b, <br />1998). Sheehan et al. (1997b) and Carlson and Pflieger (1981) noted a 3:2 ratio of hybrid sturgeon to <br />pallid sturgeon. Sheehan et al. (1997b) speculated that if this is representative of the sturgeon <br />populations in the middle Mississippi River, hybridization may pose a significant threat to pallid sturgeon <br />as the species continues to introgress with shovelnose sturgeon. <br />Table 11. Pallid sturgeon stockings from 1994 to 2000. <br />Recovery <br />Priority Areas <br />Year <br />River <br />Number Stocked <br />4 & 5 <br />1994 <br />Missouri and Mississippi Rivers <br />7,000 <br />4 & 5 <br />1997 <br />Missouri and Mississippi Rivers <br />3,000 <br />4 <br />1997 <br />Platte River <br />412 <br />6 <br />1998 <br />Atchafalya River <br />35 <br />2 <br />1998 <br />Missouri and Yellowstone Rivers <br />750 <br />4 <br />1998 <br />Platte River <br />84 <br />1 <br />1998 <br />Missouri River <br />750 <br />4 <br />1999 <br />Platte River <br />15 <br />Env. Baseline -PS 157 <br />