Ecology and structure of fish communities in the Missouri and lower Yellowstone Rivers

In the Missouri River in North Dakota, a moderately altered segment and a highly altered segment exhibited greatly different sucker communities. Bigmouth buffalo (Ictiobus cyprinellus), smallmouth buffalo (Ictiobus bubalus ), and river carpsucker (Carpiodes carpio) represented 94% of the sucker catch in the moderately altered segment, whereas in the highly altered segment, white sucker (Catostomus commersonii) and longnose sucker (Catostomus catostomus) constituted 98% of the sucker catch. In the moderately altered segment, high zooplankton densities led to greater sucker zooplanktivory and food niche overlap than in the highly altered segment.; Near the confluence of the Missouri and Yellowstone Rivers the fish community was sampled in four distinct river segments to obtain information on the distribution and habitat use of the flathead chub (Platygobio gracilis), sicklefin chub, (Macrhybopsis meeki), sturgeon chub ( Macrhybopsis gelida), and western silvery minnow (Hybognathus argyritis). Catch rates for sicklefin chub and sturgeon chub were highest in deep main channel habitat and catch rates for flathead chub and western silvery minnow were highest in shallow channel border habitat. Catches of all species were highest in the two segments least altered by anthropogenic disturbance.; The fish communities in a moderately altered segment and two highly altered segments of the Missouri River from the mouth of the Yellowstone River to Kansas City, Missouri were sampled to determine if habitat alterations can influence streamlining and structure of fish communities. In the least altered segment, higher diversity of depths and current velocities led to a fish community that was less streamlined and that exhibited greater streamlining diversity than in the two highly altered segments, which had lower diversity of depths and velocities.; One lower Yellowstone River segment and three Missouri River segments were sampled to determine if habitat changes caused by a mainstem dam had influenced niche relations among three native cyprinid species-flathead chub, sicklefin chub, and sturgeon chub. Niche relations differed among the three fish species within and among segments. The highest niche overlap among the three species was found in the two segments least altered by anthropogenic disturbance and that exhibited the greatest environmental instability.