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24 edge ~odies, and large, propulsive tails are believed to be characteristics which helped the fish maintain their equilibrium and even swim upstream in the turbulent waters. The razorback sucker is a good example. This unique fish sports a "keel" which rises just behind the head. The keel is bony since it is supported by extensions of the underlying vertebrae. Razorbacks up to one meter (3 ft) long and weighing 7 kg (10 lb) have been captured. Unlike the squawfish, the razorback is not a predator. It uses its large sucker-like lips to vacuum the silt and gravel river bottom for algae and insect larvae. However, like the squawfish, it has become rare compared to the abundant numbers reportedly taken in fishery surveys just after the turn of the century. Today, a few in- dividuals can usually be found in the Green River in Utah and in the Colorado River in western Colorado and southeastern Utah. The humpback chub is another member of this unusual group, having a broad hump which rises behind the head. In larger fish, the hump may even hang forward over the head! Its body is otherwise very streamlined. The fins are especially iarge, particularly the caudal or tail fjn which ex- tends from a slender base. The humpbaCK chub has probably never been common in the waters of the Colorado basin although it was and is fairly widely distributed. A close relative, the bony tail chub, is similar in appearance to the humpback except that the hump is not as pronounced. The bony tail is perhaps the most streamlined of the native fishes. It was more abundant at one time than it is today. Why these unusual fish have become so rare is a mystery. It is tempting to correlate their decline in numbers with the in- creased influence of man on the Colorado basin. Dams for recreation and flood control, dewatering of rivers and streams for irrigation, and in- troduction of nonnative fishes, have surely changed the physical, chemical, and biological characteristics of the river-changed them from the conditions in which these unusual humped backs, bony tails, and 45 kg minnows evolved. A Spiney Tribe Powell's first expedition ended at the mouth of the Virgin River, now flooded by the waters of Lake Meade. He arrived to find men searching for his body since it was com- mon knowledge that the rapids of the Grand Canyon were im- passable. With him were six of the spinedace. The spinedace was once so common that it Vfas collected in large numbers for use as a bait fish by anglers who called it a "shiner." In life, the body is silvery with dark specklings; the leading edge of the paired fins is orange. The spinedace reaches only about 7 cm (3 in) in length and little is known about its life history. However, recent surveys have indicated that its population is shrinking. Formerly found throughout the Virgin River system, it is now confined to -the North and East Forks of the River near Zion National Park. , The woundfin minnow: is another Plagopterini tribe . the ten men with whom he started out; four men quit the expedition along the way. Had his party ventured up the Virgin River, his boats would have passed over a fish com- munity which has some rather special members. The min- nows in the community are not unique because of their size or humps on their backs, but because they have fins with spines, a zoological rarity in the minnow family. Two species of the spined minnows are found only in the Virgin River, a silt-laden, warm- water stream in southern Utah and southeastern Nevada. Fishery taxonomists have grouped these fish, along with four other spined species, into the subfamily or "tribe" with the tongue-twisting name Plagopterini. An example of this group is ~7."'~<~ >~~' <::;~",~>~).~... . ~,~"i"- "'i4'~ . .' '~~~~J member, found only in the Virgin River. Why it is called the woundfin is unknown, but perhaps early settlers were wounded by the sharply pointed spines when they col- lected this "shiner" for use as bait. Like the spinedace, this small minnow was once com- mon throughout the Virgin River but its range has been reduced. It can now be found only in a few areas of the River and is an endangered species. HlImpback or rawrback Slicker Roundtails and Short Another rare fish in the Virgin River is the Virgin River roundtail chub. This fish demonstrates how fickle mother nature can be. The Virgin River roundtail has a very close Colorado River relative, a member of the same species in fact, though a dif-