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might vary dramatically among barrier types (e.g., complete versus partial barriers), <br />their locations within the range of the species (e.g., center of range versus peripheral <br />areas), and possible additional factors. <br />When fish passaaeways may not be warranted <br />Installing fish passageways at barriers in reaches near the upstream limits of the <br />squawfish's historic range may not be warranted if the effect of passageway use is <br />solely to provide access to habitat that is not currently limiting the population. If <br />juvenile and adult habitats are not limiting in reaches currently occupied, providing <br />access to more habitat in other reaches may not necessarily benefit the population. <br />An example of this might be found in the Colorado River reach above the Grand Valley <br />Diversion. This low-head irrigation diversion is the first in a series of three irrigation <br />diversions in river reaches near the upstream limits of both present and historic range <br />of squawfish. Fish that move upstream over the Grand Valley Diversion would <br />encounter another barrier, the medium-head Price Stub Dam (Figure 1). <br />If the dam does not have a spillway, downstream movement of all size classes of <br />fish would depend on the fish's ability to locate and use the fish passageway. <br />Moreover, before reaching the passageway fish moving downstream would have to <br />pass through a reservoir environment, which could further confound their ability to <br />locate the passageway. They might not locate the passageway. Conversely, fish that <br />successfully use a fish passageway and move upstream into the reservoir might <br />become isolated from the reproducing population; their loss could have an important <br />negative effect on population maintenance. While in the reservoir the squawfish might <br />7