Laserfiche WebLink
<br />invertebrates (principally the immature stages of insects) composed most of <br />the diet of shovel nose sturgeon, while pallid sturgeon and presumed hybrids <br />consumed a greater proportion of fish (mostly cyprinids). Other researchers <br />also reported a higher incidence of fish in the diet of pallid sturgeon than <br />. in the diet of shovel nose sturgeon (Cross 1967; Held 1969). <br /> <br />Most piscivorous Missouri River species eat large quantities of aquatic insect <br />larvae in early life and even as adults. Shovel nose sturgeon were found to <br />consume large numbers of Hydropsyche spp. and Psychomy11dae (Tricopteran <br />larvae) (Modde and Schmulbach 1977). <br /> <br />Age ~nd Growth: Little is known about age and growth of pallid sturgeon. The <br />total length of pallid lturgeon was significantly greater than that of <br />shovel nose sturgeon in the lower Missouri and Mississippi Rivers for each age <br />group in which comparable data.were available (Carlson et al. 1985). Fogle <br />(1963) estimated growth rates using cro~s sections 9f pectoral fin rays from <br />six pallid sturgeon from Lake Oahe in S9uth Dakota. He estimated that growth <br />of these fish was relatively rapid duri~g the first 4 years, but that growth <br />decreased to .approximately 70 mm (4 in)' per year between ages 5 and 10. . <br />Carlson and Pflieger (1981) presented data (n-8) from the Missouri and <br />Mississippi Rivers in Missouri, which showed slightly slower growths than from <br />pallid sturgeon in South Dakota. <br /> <br />By interpreting cross sections of pectoral fin rays, L. Jenkins (pers.. comm. <br />1991) estimated that pallid sturgeon can live more than 40.years. <br /> <br />Reasons for Decline <br /> <br />Habitat Loss: Destruction and alteration of habitats by human modifl~ation of <br />the river system is believed to be the primary cause of declines in <br />reproduction, growth, and survival of pallid sturgeon. It is unlikely that <br />successfully reproducing populations of pallid sturgeon can be recovered <br />without restoring the habitat elements (morphology, hydrology, temperature <br />regime, cover, and sediment/organic matter transport) of the Missouri and <br />Mississippi Rivers necessary for the species continued survival. ." <br /> <br />On the main stem of the Missouri River\ approximately 36 percent of riverine <br />habitat within the pallid sturgeon's range was eliminated.by construction of <br />six massive earthen dams between 1926 and 1952 and another 40 percent has been <br />channelized. The remaining 24 percent has been altered due to chal)ges in . <br />water flows caused by dam operations. <br /> <br />These dams also are believed to have ~dverse1y affected pallid sturgeon by <br />blocking migration routes and by causing inundation of spawning and nursery <br />areas. <br /> <br />i <br />Channelization of the Missouri and Mississippi Rivers began at the turn of the <br />century and continues to the present.' Channelization causes changes in water <br />velocity, reduces the width of the river, and prevents water flow into <br />backwaters. In the channelized reach downstream of Sioux City,Iowa, the <br />Missouri River that was once a diverse assembledge of braided channels, <br />sandbars, and backwaters is now confined within a narrow channel of rather <br /> <br />10 <br />