7112 - Laserfiche WebLink

Home Browse Search

lzz Ft. Thomas on the mainstream of the Gila (Kirsch, 1889), and farther up- stream." The comparable decline in abundance of squawfish in the Colorado River mainstream, below Lake Mead, as indicated in the quotation by Miller (19616)'given above, has appeared to continue to essential ex- tinction. Minckley & Deacon (1968) heard of only two specimens from that region between 1962 and 1967 (one of which was seen and was from Lake Mead itself), and none has been reported subsequently. There is no published information on the life history of this fish in Arizona waters. Vanicek & Kramer (1969) have provided data, •~owever, from the Green River in Dinosaur National Monument, and some informa- tion may be gleaned from a number of general publications (Simon, 1951; Beckman, 1963; Sigler & Miller, 1963; and others). Prior to dams, squaw- fish moved upstream in "runs" just before the spawning period. This, along with their great size, presumably result in the name "salmon." Other squawfishes, P. grandis (Ayres) of the Sacramento River basin (Taft & Murphy, 1950) and P, oregonensis (Richardson) (citations below), also seem to "run" into streams to spawn, at least in the past. Reproduction by Colorado River squawfish in the Green River appeared to occur in July and August, attuned to increasing water temperatures and receding water levels. In the southern part of its range, and perhaps in the Green River, Utah, before moderation of temperatures induced by damming, spawning must have occurred earlier in the year. Young, 32 mm long, were taken in mid-May in Arizona (Miller, in Sigler & Miller, 1963). Spawning by other species of Ptychocheilus occurs in early to late spring. Actual spawning sites or breeding behavior of P. lucius has yet to be observed. The northern squawfish (P. oregonensis) spawns in lakes or streams of the Columbia River basin, in shallow water over gravel or rubble (Jeppson & Platts, 1959), or in streams over larger rubble in riffles or at the lower ends of pools in tributaries (Keating, in Vanicek & Kramer, 1969). Spawning by P. grandis seems to occur at the lower ends of pools, just above riffles, or in riffles (Taft & Murphy, 1950). Spawning behavior of P. oregonensis in Merwin Reservoir, Washington, has recently been de- scribed in detail by Patten & Rodman (1969). Fish congregated in in- creasingly greater numbers from June, to a peak of reproductive activities in the first week of July. They were over a specific area of rocky bottom, deeper than three meters, but above the thermocline. Swarms of males moved slowly and irregularly about 30 cm above the bottom, with indi- viduals darting abruptly upward, then returning to the swarm. The 11F. W. Chamberlain's 1904 field notes report as follows: "Several years ago fish were abundant (near Safford, Graham County, in the Gila River). Then pools of sufficient depth for men to swim in existed. Salmon reached a weight of 35 Ib., humpback and other suckers were abundant. None of these has been taken in the last two years. It is believed that minerals and concentrate-wash from the mines and works at Morenci and Clifton have killed the fish." 123 boulders beneath the swarm were cleaned, presumably by current created by the moving bodies, while those in other places were covered by sedi- ment. Females swam alone, peripheral to the swarm of males. When a female moved near, 2 to 3 males usually chased her as she accelerated to an open area, attempting to maintain position with their snout near the female's vent. A female followed by males dipped near the bottom, usually over a crevice, recurved her back, and spawned with vibratory, lateral movements. Males moved over and about her in a "solid mass," presumably emitting sperm. Only a small number of eggs was released at a time, so a female must have performed the act repeatedly to deplete her ovaries. The eggs adhered to the substrate (as has been noted in other spe- cies); however, none was found on the upper surfaces of stones. Unpro- tected eggs were likely eaten by predators. Young of P, lucius appeared in August in all three years that Vanicek & Kramer (1969) studied the Green River population, 3 to 6 weeks after the estimated time of spawning. Growth of the young fish continued throughout the year, and by the end of their third summer juveniles were averaging about 160 mm in total length. The largest specimen taken by them was 600 mm total {ength, about 1.85 kg in weight, and was 11 years of age. Foods of Colorado River squawflsh in the Green River consisted of crustaceans and aquatic dipteran larvae when the fish were shorter than 50 mm total length. An increasing number of aquatic insects, plus terrestrial insects, was taken when the fish were between 50 and 100 mm, and other fishes predominated the diet of specimens longer than 101 mm. There was an increasing incidence of empty stomachs in larger fish, reflecting perhaps the sporadic nature of feeding o#ten found in piscivores. Large adults of P. lucius have been known to take carcasses of small animals and birds (Beckman, 1963), and they also have been caught on artificial lures (as has P. grandis; Taft & Murphy, 1950). Relatively complete studies of foods of other squawfish are those of Chapman & Quistorff (1938) and Thompson (1959) for P, oregonensis, and notes of Taft & Murphy (1950) for P. grandis. The last two species, and P. umpquae Snyder, are often thought to be severe competitors of, and predators upon, trouts and sal- mons, and have been subject to intensive research for eradication and control in areas where they are abundant (references already cited, and MacPhee & Ruelle, 1969). It is notable that the other three species of squawfishes appear to be maintaining populations in their native ranges, whereas P. lucius is declining; the reasons for this are unknown. As has been repeatedly implied, Colorado River squawfish, and most other species of this genus, are big-river fishes, characteristic of waters deeper than a meter and generally with strong to moderate cur- rents. Young frequent backwaters over almost any bottom type, where currents are slight or absent. - Carhart (1950), Miller (in Minckley, 1965a), Joseph Stone, Arizona Game and Fish Department (pers. comm.), and a number of the "old