WSP06973 - Laserfiche WebLink

Home Browse Search

It is also suspected that increased clarity of the Missouri River has affected food availability by changing species composition and by making it more difficult for pallid sturgeon, and other native species, to capture prey in the clearer water environment. In the Missouri River, pelagic planktivores and sight-feeding carnivores have increased in abundance, whereas species specialized for life in the turbid, predevelopment river (like the pallid sturgeon) have decreased in abundance (Pflieger and Grace 1987). This change in conunun ity structure is 1 ess apparent where changes in the natural hydrograph, temperature regime, and turbidity are less pronounced. Flood flows were essential for the dynamic transport of sediment and the re- arrangement of these sediments into natural morphological channel features (fish habitat); it served to introduce and transport organic matter from the floodplain; and to maintain turbidity. Flood flows were the principle method for the introduction of large woody debris and carried nutrients to floodplain plant communities, which determined floodplain forest composition and .. . structure. Invertebratereproductjon and behavioral migration was closelY tied to the natural hydrograph (Hesse and Mestl 1993c). Nearly all snags were removed from the Missouri River between 1838 and 1950. This, plus the cessation of flooding and meandering as a result of danuning and channelizing the river has reduced the availability of organic matter.supplies util ized by ihe aquatic invertebrate conununity (Hesse and MestlI993a). Snags influence.sedimont routing', thus creating pools, gravel bars, and depositional areas, which in'turn reduce the' rate of downstream transport of particulate organic matter (Bilby and Ward 1991; Bilby and likens 1980). Snags also provide habitat for aquatic insects that make up a large proportion of both the.shovelnose and pallid sturgeon's diet. These insects are . collector-filterer-gatherers (Merritt and Cummins 1984).. They cling to large woody debris in high velocity areas, gathering drifting diatoms, algae, .animals, and organic detritus. Mestl and Hesse (1993) documented a decl ine in the abundance of snag insect production of more than 65 percent in Nebraska's portion of the Missouri River between 1963 and 1980. In spite of man's efforts to constrict and control the Missouri and Mississippi Rivers with reservoirs, stabilized banks,. jetties; dikes, levees andreventments that result in impacts described above, remnant reaches of the Missouri River and the Mississippi River from the Missouri River confluence.to the Gulf still provide habitat believed usable by pallid sturgeon. These remnants described later as Recovery-Priority" Management Areas are priority areas for implementation of recovery actions. Commercial Harvest: Historically, pallid, shovelnose,and lake sturgeon were commercially harvested on the Missouri and Mississippi Rivers (Helms 1974). The larger lake and pallid sturgeon were sought for their eggs which were sold as caviar, whereas shovel nose sturgeon were destroyed as a bycatch. Conunercial harvest of all sturgeon has declined substantially since record keeping began in the late 1800's. Most commercial catch records for sturgeon have not differentiated between species. Combined harvests as high as 195,450 kg (430,889 lbs) were recorded in the Mississippi River in the early 1890's, but had declined to less than 9,100 kg (20,062 lbs) by 1950 (Carlander 13 T