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populations are also examined. The chapter concludes with a discussion of possible management options to slow or reverse the decline of humpback chub numbers. Background The Colorado River was one of the last areas of the continental United States to be explored by Europeans; it was first traversed during the expedition headed by John Wesley Powell in 1869. For this reason, it is not surpris- ing that scientific descriptions of many of the organisms in the Colorado River corridor, especially the fishes, did not begin until the 1930s and 1940s; earlier expe- ditions collected and described fishes generally rather than specifically. Emery and Ellsworth Kolb, explorers and photographers of the Colorado River in the early 1900s, reported that fishes were very abundant (Kolb and Kolb, 1914). The humpback chub was the last of the native fishes in Grand Canyon to be described in 1946 by Robert R. Miller from specimens taken from the Colorado River in Grand Canyon (Miller, 1946). Scientific description or the native fishes or Grand Canyon showed that these species were unique in at least two ways. Most noticeably, several of the species share unusual body shapes, including large adult body size, small depressed skulls, large predorsal humps or keels, and small eyes, which presumably developed as adapta- tions to life in a large, turbid, and seasonably variable riverine environment. These features are perhaps best observed in the razorback sucker (Xyrauchen lexanus) and the humpback chub (see accompanying text box, p. 51). A second, and perhaps more important, measure of the uniqueness of Grand Canyon native fishes is that most of these species are not found elsewhere in the world. Organisms that are native to a certain location and do not occur anywhere else are called endemic spe- cies. Of the eight native species common to the Grand Canyon, six are species endemic to the Colorado River Basin. As early as 1895, scientists recognized the special nature of Colorado River fishes and the high rates of endemism (Minckley, 1991). Later research did not alter this conclusion, and despite a relatively low number of species compared to other drainages in the United States, the Colorado River Basin has a recognized ende- mism at the species level of approximately 75% and sup- ports the most distinctive ichthvofauna in North America (l'vIinckley, 1991). . Before European settlement, the native fishes found in the Grand Canyon portion of the Colorado River were exclusively minnows and suckers. The biggest of Fishes of Grand Canyon 35 these fish was the Colorado pikeminnow (PtycllOclzdlus lucius), which is also the largest of all native minnow (cyprinid) species in North America and was found only in the Colorado River Basin (fig. I). Called a white salmon by early settlers, the Colorado pikeminnow reached up to 6 ft (2 m) in length and had a weight of up to 80 Ib (36 kg) (Mueller and Marsh, 2002). Today, three of the eight native fish species have been eliminated from the Colorado River in Glen and Grand Canyons (roundtail chub (Gila robusla), bony tail chub (Gila elegans), and Colorado pikeminnow), and two are federally listed as endangered (humpback chub and razorback sucker) under the Endangered Species Act. Although listed as an endangered species with designated critical habitat in Grand Canyon, the razorback sucker has rarely been collected (Minckley, 1991; Valdez and Carothers, 1998) and is widely thought to no longer be found in Grand Canyon. The status of the flannelmouth sucker (Caloslomus lalipinnis) is common, and the species persists in the study area and throughout much of the upper Colorado River Basin. The remaining two fish (bluehead sucker (Caloslomus disco bolus) and speckled dace (Rlziniclzlfrys osculus)) are relatively common. Brief descrip- tions of the life histories of all the Grand Canyon native fishes can be found in Minckley (1991); this chapter provides text boxes (see p. 50) with summary information for the four native fishes that continue to inhabit Grand Figure 1. Historical photograph (date unknown) of someone identified as James Fagen holding a large Colorado pikeminnow in lower Granite Gorge (courtesy of the Kolb Collection, Cline Library, Northern Arizona University, NAU.PH.568.57371.