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Figure 21. Vegetation, mostly saltcedar and honey mesquite, flooded during <br />1983. Mesquite died rapidly. Note debris piled in open lanes and the renewed <br />saltcedar growth under these conditions. Photo by D. Krueper. <br />1960's (Figures 22A,B,C). Another <br />species, the desert pupfish <br />(Qyorinodon macularius), was a species <br />of marshes and backwaters and has not <br />been recorded from the mainstem river <br />since the early 1900's. <br />The present fish fauna of the <br />lower Colorado River is composed al- <br />most exclusively of introduced <br />species. Of the 24 introduced species <br />(Minckley 1979), 16 are from the Mis- <br />sissippi River Valley region, 4 are <br />from the Old World, 2 are from Middle <br />America, and 2 are anadromous (one <br />from the Atlantic and the other from <br />Pacific drainages). The declines in <br />the native ichthyofauna are related to <br />both habitat changes and interspecific <br />interactions (including competition <br />and predation) from introduced species <br />and are discussed in more detail in <br />Chapter 9. <br />jor <br />Figure 22A. Three species of South- <br />western big-river fishes that were all <br />once abundant in the lower Colorado <br />River. Bonytai l chub (Q la elggas) <br />is now found only in very low numbers <br />at Lake Mohave, while it is apparently <br />extirpated throughout the rest of its <br />historical range. Photo by W.L. <br />Minckley. <br />27