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}c. =~-~ :.,~ . ~, ~k ,~: ~: `! 4 ~4 a~ M. i to this discussion are the Colorado River squawfish, Ptychocheilus Lucius, and the humpback sucker, Xyrauchen texanus. The status of these fishes above Grand Canyon, particularly in the Green River, has been outlined by Van- icek (8). Both species were effectively eliminated from about 250 miles (400 kilometers) of the mainstream and 250 miles of tributaries of the Green River above the Flaming Gorge Dam site by fish-control operations in 1962, some kill being observed downstream as far as Dinosaur National Monument (9). Neither species is now found above the dam, or in the 65-mile stretch of cold tail-waters between Flaming Gorge Dam and the mouth of the Yampa River in Dinosaur National Monument. Both squawfish and humpback sucker, however, are common in the Green River between Echo Park (Yampa River) and Ouray, Utah. Koster (10) reported adult squawfish (and possibly humpback- suckers) from the San Juan River, in New Mexico, in 1959. He pointed out, however, that the segment of river from which the fish were ob- tained was soon to be flooded by the construction of Navajo Dam. squaw- fish ran to the base of Grand Falls on the Little Colorado River in years past (11), but that area is now essentially dry. We have seen, or heard of, two adult or subadult squawfish taken from the Colorado River between Glen Can- yon Dam and Lee's Ferry in the period 1962-66. No humpback suckers have been seen in that segment of the river, but one hybrid, Xyrauchen texanus X Catostomus latipinnis, was taken be- low Glen Canyon in 1966 [such hybrids have previously been reported by Hubbs and Miller (12)]. On the basis of these data and of a general account by Sigler and Miller (13), it appears that both squawfish and humpback suckers are persisting above, and in, Grand Canyon. We leave further documentation of their status in that area to others. For the region below Grand Canyon our data are specific. Colorado River squawfish were abundant at Yuma in the early 1900's, and in the lower Gila River near Dome in 1920 (4). They per- sisted in the lower Colorado mainstream until the 1940's (/4), but since 1950 they have become increasingly uncom- mon. We have heard of only two speci- mens from the lower Colorado in the period 1962-67. In historic times, squa~efish lived- in the Gila River mainstream as far east as Ft. Thomas, in the San Pedro River 1426 at least to Fairbank (1S), and in the Verde River to Camp Verde (16), and presumably they were present through- out the Salt River Canyon and above it (4, 17). We have collected intensively in the Gila River basin since 1963 and can attest to the virtual, and perhaps actual, extinction of both squawfish and hump- back sucker there. The headwaters of the Gila River were blocked by Coo- lidge Dam in 1929 (7); the river is now a dry wash throughout most of its lower course. The formerly large San Pedro River rarely flows in its lower part, and is a small creek near its headwaters. The Verde and Salt rivers are effectively im- pounded, and the upper Verda has diminished flow and is entrenched in its ftoodplain (16). Only the Salt River, in its central canyon, seems a suitable habitat for either squawfish or hump- back sucker. No adult squawfish has been taken from the Roosevelt area on the Salt River since 1937 (4). Dammann (see 17) saw two adults taken in the Salt River Canyon in 1948, however, and Miller (4) caught two young squawfish near the same locality in 1950. Branson et al. (18) reported seven juvenile speci- mens seined in the canyon in 1959. We and other. workers known to us have failed to obtain any squawfish or hump- back suckers since 1963, during inten- sive studies of that area, and John K. Andersen (19) of the U.S. Bureau of Sport Fisheries and Wildlife, who has worked in the canyon for the past few years, has not taken either of these fishes in his sampling program, or seen either in fishermen's creels. The habitats of humpback suckers and squawfish are similar, though the suckers are more likely to frequent marshes, lakes, and quieter parts of rivers. Humpback suckers have been less commonly reported than squawfish, perhaps because humpback are less easily taken by conventional fishing methods. The recent status of the spe- cies in part of the upper Colorado is given by Vanicek (8). Below Grand Canyon it appears to be maintaining a fairly constant abundance. Norman ~'Vood (30} of the Nevada Game and Fish Commission has found no changes in the numbers of humpback observed in lakes Mead and lviojave over the last 15 years. However, his conclusion is based on casual observations made during fish-population census, and no actual data are available. Spawning ag- gregations of this species were observed several times in the lakes (_'1), most recently in \larch 1967 in a shallow cove of Lake Mojave (20}. The sucker also persists farther downstream, in Lake Havasu and below, perhaps as far as Martinez Lake (where, according to local testimony, one was seen in 1966), but it is becoming increasingly rare. The upstream limit of range of humpback suckers in the Gila River basin was probably similar to that of squawfish. The suckers were abundant enough to be marketed is Tombstone, as "buffalo fish," prior to tli~ 1880's (4, IS); presumably these specimens were caught in the adjacent San Pedro River. We know of no records of humpback suckers from the Gila River mainstream above Phoenix, or from the \%erde River, but large populations formerly were present in the Salt River. Accord- ing to Hubbs and Miller (12), the fixh was common near Roosevelt, Arizona, prior to the closure of Roosevelt Dam. In 1926, many suckers were seined in Roosevelt Lake and in Tonto Cree{; up- stream from the lake, but none is now found in either area (7.2}. The large populations persisted until the 1950's in lakes downstream from Roosevelt; com- mercial fishermen took 6 tons of hump- back from Saguaro Lake in 1949, but none was found when the lake was drained in 1966 (22). We point out again that both these fishes appear to be maintaining popula- tions in some areas of the Colorado River basin, yet the relatively well- documented decline of both in the Gila River basin is instructive, and may fore- shadow their extinction elsewhere. Large fishes like squawfish and hump- back sucker have long life expectancies, and the presence of large adults may not indicate a "healthy" population. The large average size of humpback suckers in the Salt River impoundments in 1949 [some weighed more than 14 pounds (6 kilograms) and were more than 30 inches (75 centimeters) long (12)] may have foreshadowed their imminent de- cline through lack of reproductive suc- cess. Despite observations of the spawn- ing of humpback in the lower Colorado River lakes, no specimen shorter than about 15 inches has been caught in re- cent years (20-22). One can hardly say that such fishes are "maintaining their populations," and only long-range trends are available as a basis for estimating their status. There are few basic data available on the ph}•siological, ecological, or behav- ioral requirements for their continued reproductive success. It is easy to say that such big-ri~•er fishes disappear as a SCTENCE, VOL. 159 _ _ __