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<br />.' <br /> <br />.' <br /> <br />Basin is known to migrate into a tributary to spawn, as occurs in the Little Colorado River within <br />the Grand Canyon, Larry Crist. U.S. Bureau of Reclamation, personal communication). Detailed <br />information about spawning and rearing is lacking for both humpback chub and razorback sucker <br />throughout the Upper Basin. And. of course. virtually nothing is known about bony tail chub. <br />, . <br /> <br />Moreover, accurate estimates of annual population size remains elusive for all of the fishes (Tyus <br />1992), and properly designed mark-recapture studies using the new transponder tag technology <br />clearly are warranted. On the other hand, a great deal more is known about the distribution and <br />abundance of the fishes, excepting bony tail chub. than is known about the influences of river <br />hydraulics. sediment transport and riparian controls on the longitudinally dynamic food web that <br /> <br />clearly supports the fishes. In other words, the data upon which current flow recommendations are <br />based primarily describes the distribution and abundances of the fishes, not the ecosystem-level <br />processes and responses that determine productivity. <br />3) Strong linkages between trophic (food web) and geomorphic attributes of the Upper <br />Colorado River Basin ecosystem are dynamic, or variable, in time and space. For example, algae <br />(periphyton) and zoobenthos communities are more productive on cobble bars than sand, but <br />substratum size on river bars is highly variable in time and space as a function of the dynamic <br />sediment transport and deposition processes that occur as the river fluctuates between peak and <br /> <br />baseflows (Figure 2). Another example, though not well documented, is the propensity for high <br />benthic and planktonic production in subchannels (backwaters) and floodplain wetlands that were <br />(predam) seasonally pulsed and predictable. These different. yet interactive, space and time scales <br />that produce natural biophysical variation are the essence of the ecosystem in which the endangered <br />fishes evolved and must be documented thoroughly. <br />4) Studies to date in the Upper Colorado River Basin strongly infer that flow regulation, <br />specifically reduction of the amplitude between peak- and baseflows, is a likely contributor to the <br />decline of the native fishes. But, cause and effect are not simple relationships. For example, it <br />appears that years of regulated flows, coupled with construction of revetments, have reduced the <br />availability of backwaters and wetlands as nursery habitats that support larval and juvenile <br /> <br />42 <br />