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— Sturgeon chub: Once reported from 14 states, this species is probably extant in only
<br />5 states (Werdon 1993b). USFWS (2001) reported that the species exists in 11 of 30
<br />tributaries (37 %) that supported sturgeon chub habitat. Hesse (1994) reported that
<br />sturgeon chub were either extirpated or present in such low numbers as to be
<br />functionally extirpated in the Missouri River in Nebraska. The fish has been listed as
<br />threatened, endangered, or a species of concern in Kansas, North and South Dakota,
<br />Missouri, Kentucky, Tennessee, Missouri, Nebraska, Montana, and Wyoming (Power
<br />and Ryckman 1998, USFWS 1995, 2001). The fish is considered extirpated from Iowa.
<br />The sturgeon chub is morphologically adapted for life in turbid plains rivers. The
<br />slender fish has a depressed head, small eyes, highly developed olfactory structures,
<br />and unique dermal keels (Branson 1966, Cross 1967, Reno 1969).
<br />— Sicklefin chub: Once reported from 13 states, this species is probably extant in only 4
<br />states (Werdon 1993a). Hesse (1994) reported that sicklefin chub were either extirpated
<br />or present in such low numbers as to be functionally extirpated in the Missouri River in
<br />Nebraska. The fish has been listed as threatened, endangered, or a species of concern
<br />by Kansas, Iowa, Missouri, North Dakota, South Dakota, Kentucky, Tennessee, Kansas,
<br />Nebraska, and Montana (Werdon 1993a, Power and Ryckman 1998, USFWS 1995,
<br />2001).
<br />The sicklefin chub is specialized for living in the main channels of large turbid
<br />rivers, where it is adapted to deep water, strong currents, and turbid water (Cross 1967).
<br />The fish has small eyes that are partially covered to protect them and abundant sensory
<br />structures for detecting prey in dim light (Moore 1950, Reno 1969). This fish is unique
<br />among other barbeled minnows due to its very long pectoral fins. Threats to the survival
<br />of this fish include habitat fragmentation, habitat loss and alteration, competition and
<br />predation from introduced fishes, and contaminants (Werdon 1993a).
<br />— Flathead chub: Historically one of the most abundant fishes in the Missouri River,
<br />numbers of the fish sharply declined beginning with the construction of large mainstream
<br />reservoirs. Formerly amounting to 31 % of small fishes taken in seine hauls in the
<br />1940's, by the 1980's the fish was only 1.1% of collections (Pflieger 1997). This decline
<br />was also documented by Hesse (1994) in the Missouri River in Nebraska, where the fish
<br />declined in catch/effort 98% from 1971 to 1993. The flathead chub has been listed as
<br />endangered or a species of concern in Missouri, Arkansas, Kansas, and North Dakota.
<br />The flathead chub is a rather large (to 12'/2 in) barbeled minnow, having a
<br />distinctive broad and flattened head, and large pointed sickle- shaped dorsal and
<br />pectoral fins (Page and Burr 1991) . The fish has small eyes and depends more on
<br />external taste buds to find food in its native turbid water environment (Pflieger 1997).
<br />Clear water conditions places the fish at a disadvantage with introduced, sight- feeding
<br />fishes. It is presumably in competition with the emerald shiner, whose numbers have
<br />increased as flathead chubs have decreased (Pflieger 1997). Predation on its young by
<br />introduced predators, such as walleye or largemouth bass is likely a factor in its decline.
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