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<br />ECOLOGY AND CONSERVATION OF NATIVE FISHES IN THE UPPER COLORADO RIVER BASIN <br /> <br />167 <br /> <br /> <br />UTAH <br /> <br />- <br /> <br />ARIZONA <br /> <br />Farmington <br /> <br />WYOMING <br /> <br />1( <br /> <br /> <br />COLORADO <br /> <br />\00 ISO ZOO <br />. <br /> <br />SCAlE Of KILOMETERS <br />o 50 100 <br />>~- ..... . <br />SCAlE Of MILES <br /> <br />250 <br />, <br /> <br />so <br /> <br />'50 <br />. <br /> <br />- -_. ----- <br /> <br />--- <br /> <br />NavajO ReSi!J1VOlf NEW MElOCO <br /> <br />Figure 5.-Present distribution of wild razorback sucker (shaded) in the upper Colorado River basin. <br /> <br />spawning periods (T yus 1987; Valdez and Masslich <br />1989; T yus and Karp 1990). In upper basin riverine <br />environments, spawning is during spring runoff from <br />mid-April to June. Average fecundity is about 46,740 <br />eggs per female and maximum is 103,000 (Inslee <br />1982; McAda and Wydoski 1980). Adults stage in <br />floodplains, gravel pits, large backwaters, and im- <br />pounded tributaries near spawning sites (Holden and <br />Crist 1981; Valdez and Wick 1983; Tyus 1987; <br />Osmundson and Kaeding 1989; Tyus and Karp <br />1990; Modde and Wick 1997; Modde and Irving <br />1998; Osmundson et al. 1995), and spawn over large <br />mid-channel cobble bars at an average water tem- <br />perature of about 150C in velocities less than 1.0 m/ <br />s and depths of less than 1.0 m (McAda and Wydoski <br />1980; Tyus 1987; Tyus and Karp 1990; Bestgen <br />1990; Wick 1997). Incubation at 18-20oC is 6-7 d <br />(Snyder and Muth 2004), and larvae drift with river <br />currents into food-rich floodplains, where densities <br /> <br />of benthos and zooplankton may be 157 times greater <br />than in the main channel (Mabey and Shiozawa <br />1993). Razorback sucker are omnivorous and con- <br />sume principally insects, zooplankton, phytoplank- <br />ron, algae, and detritus (Bestgen 1990). Larvae de- <br />velop a terminal mouth at 10-11 mm TL and feed <br />on planktonic cladocerans, rotifers, algae and midge <br />larvae that decrease in importance as the mouth mi- <br />grates to a subterminal position for benthic feeding <br />(Marsh and Langhorst 1988; Muth et al. 1998). <br />Pathogens include bacteria Erysipelothrix rhysi- <br />opathiae, protozoa (Myxobolus sp., can cause blind- <br />ness; Minckley 1983) and the parasitic copepod <br />Lernaea cyprinacea (Flagg 1982). <br /> <br />Roundtail Chub <br /> <br />Roundtail chub have a cylindrical body that is <br />slightly compressed laterally and is silvery-green <br />