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Correspondences Concerning Upper Colorado Biological Opinions 1993
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Correspondences Concerning Upper Colorado Biological Opinions 1993
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Correspondences Concerning Upper Colorado Biological Opinions 1993
State
CO
Date
11/30/1993
Title
Correspondences Concerning Upper Colorado Biological Opinions 1993
Water Supply Pro - Doc Type
Biological Opinion
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Ira W. Hatch, District Ranger 9 <br />suckers from some localities, coupled with the species' continued decline in <br />numbers and distribution, has prompted some research; however, details of its <br />life history requirements, particularly in riverine environments, are still <br />not fully understood. <br />In general, a natural hydrograph with a large spring peak, a gradually <br />descending limb into early summer, and low stable flows through summer, fall, <br />and winter are thought to create the best habitat conditions for endangered <br />fishes while maintaining the integrity of the channel geomorphology. Prior to <br />construction of large main stem dams and the suppression of spring peak flows, <br />low velocity, off - channel habitats (seasonally flooded bottomlands and <br />shorelines) were commonly available throughout the Upper Basin (Tyus and Karp <br />1989; Osmundson and Kaeding 1991). The absence of these seasonally flooded <br />riverine habitats is believed to be a limiting factor in the successful <br />recruitment of razorback suckers in their native environment (Tyus and Karp <br />1989; Osmundson and Kaeding 1991). Tyus (1987) and McAda and Wydoski (1980) <br />reported springtime aggregations of razorback suckers in off - channel <br />impoundments and tributaries that were believed to be associated with <br />reproductive activities. Tyus and Karp (1990) and Osmundson and Kaeding <br />(1991) reported off - channel habitats to be much warmer than the main stem <br />river and that razorback suckers presumably moved to these areas for feeding, <br />resting, sexual maturation, spawning, and other activities associated with <br />their reproductive cycle. While razorback suckers have never been directly <br />observed spawning in turbid riverine environments within the Upper Basin, <br />captures of ripe specimens, both males and females, have been recorded (Valdez <br />et al. 1982; McAda and Wydoski 1980; Tyus 1987; Osmundson and Kaeding 1989; <br />Tyus and Karp 1989; Tyus and Karp 1990; Osmundson and Kaeding 1991; Platania <br />1990) in the Yampa, Green, Colorado, and San Juan Rivers. Sexually mature <br />razorback suckers are generally collected on the ascending limb of the <br />hydrograph from mid -April through June and are associated with coarse gravel <br />substrates (depending on the specific location). <br />Outside of the spawning season, adult razorback suckers occupy a variety of <br />shoreline and main channel habitats including slow runs, shallow to deep <br />pools, backwaters, eddies, and other relatively slow velocity areas associated <br />with sand substrates (Tyus 1987; Tyus and Karp 1989; Osmundson and Kaeding <br />1989; Valdez and Masslich 1989; Osmundson and Kaeding 1991; Tyus and Karp <br />1990). <br />Habitat requirements of young and juvenile razorback suckers in the wild are <br />largely unknown, particularly in native riverine environments. Life stages, <br />other than adults, have not been collected anywhere in the Upper Basin in <br />recent times. The last confirmed documentation of a razorback sucker juvenile <br />in the Upper Basin was a capture in the Colorado River near Moab, Utah (Taba <br />et al. 1965, reported in Bestgen 1990). <br />Humpback Chub <br />Humpback chub generally do not make migrational movements in the upper <br />Colorado River and tend to reside throughout the year within a limited reach <br />of river. Humpback chub are found inhabiting narrow, deep canyon areas and <br />are relatively restricted in distribution. They seldom leave their canyon <br />
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