Part 4

Hybopsis gracilis physignathus, Beckman, 1952:50 (characters; habitat).

Hybopsis gracilis, Eddy, 1957:111 (in part; characters; key); Koster, 1957:61 (characters; habitat; spawning; food); Moore, 1957:110 (in part; key); Smith, 1958:177 (fossil record; Doby Springs, Okla.).

Diagnosis.--Post-Weberian vertebrae 36-38, rarely 39; lateral line scales 42-54, usually less than 50; pectoral rays 14-19, usually fewer than 17; head-depth 13.5-18.0 per cent of standard length, usually 14.8 per cent or more. See Figures 1 and 2.

Other characters.--Circumference scale-rows 30-40, slightly fewer than in H. g. gracilis; predorsal scale-rows 17-27, somewhat fewer than in specimens from Canada, but much the same as specimens from the Missouri-Mississippi system; size small, rarely as much as 130 mm standard length (Fig. 1 of Pl. 24); head-length 24.0-28.0 per cent of standard length, usually more than 25.5 per cent; postorbital length of head 11.2-14.4 per cent of standard length, usually more than 12.5 per cent (both characters illustrate the larger head of H. g. gulonella); predorsal length 46.4-52.7 per cent of standard length, longer than in the other subspecies; orbit 5.0-6.6 per cent of standard length; prepelvic length 47.4-53.7 per cent of standard length, longer than in H. g. gracilis; caudal peduncle length 17.1-22.7 per cent of standard length, essentially the same in both subspecies.

The label on types of this subspecies, in the Academy of Natural Sciences of Philadelphia, states merely "near Bridger's Pass, Wyo., Expedition of 1856, Dr. W. A. Hammond" (letter from Dr. James Boehlke to Cross, dated Jan. 27, 1960). Dr. Hammond was a surgeon who also collected scientific specimens, assigned to an expedition under the command of Lt. F. T. Bryant. Bryant's log is recorded in the Proceedings of the 35th Congress (1858:455-481). The site at which these specimens were taken cannot be ascertained from the log, but study of it is helpful in indicating the probable locations.

The expedition left Fort Riley on June 21, 1856, on the following route: up Republican River; across to Fort Kearney on Platte River; west along Platte River to S. Platte River; up S. Platte River to Pole (Lodgepole) Creek; Pine-Bluffs (Neb.-Wyo. line); across East Fork to West Fork of Laramie River; Cooper's Creek; West Fork of Medicine Bow; Pass Creek and down canyon of Pass Creek; across N. Platte River; up Sage Creek; on August 15, camped on Muddy Creek, tributary to Green River (first record of fish, trout); back to Sage Creek; August 19-21, camped on island in North Platte River; to Pass Creek; Elk Creek; west branch of Medicine Bow; Aspen Creek; West Fork of Laramie River; August 29, to East Laramie River where a large supply of fish was caught; tributary of Cache la Poudre then downstream to mouth of this river; down South Platte River past mouth of Crow Creek and Beaver Creek; left South Platte River 14 miles below mouth of Beaver Creek, toward Republican River; down Rock Creek to Arikaree; down Arikaree to Republican River and down the Republican to Fort Riley.

Mention is made of fish only twice in the entire log. We doubt that Muddy Creek or the East Laramie River is the type locality of P. gulonellus, because the flathead chub has not since been found in either of these streams. The most likely collection site for P. gulonellus is the North Platte River near the mouth of Sage Creek, in what is now Carbon County, Wyoming, where the expedition was camped for three days. This species is known to occur in the North Platte River, and since the type locality is reported as "near Bridger's Pass" this is the probable location.

Range (Plate 21).--Upper mainstream and tributaries of Rio Grande, Pecos, Arkansas and North Platte Rivers; isolated populations in tributaries of the upper Missouri River.

Specimens examined.--Below are listed museum numbers, number of specimens (in parentheses), localities and year of collection. Series marked by asterisks (*) are intergrades tending toward H. g. gulonella. Literature reports are cited in the synonymy.

COLORADO: KU 4742 (162), Bent Co., Purgatoire R. at Las Animas, 1959; KU 4748 (105), Pueblo Co., Arkansas R. at west edge of Pueblo, 1959; KU 4758 (50), Fremont Co., Arkansas R. at Florence, 1959; KU 4769 (64), Fremont Co., Beaver Cr., 1959.

KANSAS: KU 2648 (2), Finney Co., Arkansas R., 1958; KU 2858 (13), Finney Co., Arkansas R. at Garden City, 1951; KU 3964 (12), Kearney Co., Arkansas R., 1958; * KU 4041 (2), Cheyenne Co., Republican R., 1958; KU 4732 (30), Hamilton Co., Arkansas R. at Kendall, 1959; * KU 4868 (1), Kansas-Nebraska line, Republican R. 1.5 mi. S. Hardy, 1959.

MONTANA: * MSC 1960 (8), Powder River Co., E. Fork of Powder R., 1957; MSC 2010 (64), Dawson Co., Redwater R., 1957.

NEBRASKA: * KU 2140 (2), Dawson Co., Platte R., at Gothenburg, 1931; * KU 4863 (20), Furnas Co., Republican R. at Cambridge, 1959; * UM (field no. 59-49) (74), Scotts Bluff Co., North Platte R. at Morrill, 1959; * UMMZ 133918 (17), Dixon Co., Logan Cr., 1939; * UMMZ 134813 (31), North Platte R., Neb.-Wyo. line, 1941; * UMMZ 135084 (14), Harlan Co., Beaver Cr. 0.25 mi. S Stamford, 1940; * UMMZ 135200 (41), Scotts Bluff Co., North Platte R. 1 mi. SE Henry, 1940; * UMMZ 135280 (59), Cherry Co., Niobrara R. 3 mi. SE Valentine, 1940; * UMMZ 135700 (25), Buffalo Co., South Loup R. 8 mi. N Miller, 1941; * UMMZ 135778 (54), Thurston Co., Logan Cr. 2.5 mi. W Pender, 1941; * UMMZ 135786 (25), Dixon Co., Logan Cr. 0.5 mi. NW Wakefield, 1941.

NEW MEXICO: KU 4219 (50), Colfax Co., Cimarron Cr. at Springer, 1958; KU 4235 (19), Mora Co., Sapello Cr. near Sapello, 1958; KU 4245 (157), Bernalillo Co., Rio Grande 12 mi. S Bernalillo, 1958; KU 4255 (22), Rio Arriba Co., Rio Grande at Velarde, 1958; KU 4266 (53), Sandoval Co., Rio Grande 2 mi. N Cochiti Pueblo, Marcelino Baca bridge, 1958; KU 4269 (91), San Miguel Co., Pecos R., 3 mi. S Pecos, 1958; KU 4274 (25), Sandoval Co., Jemez R. at Jemez Canyon Dam, 1958; KU 4294 (113), Guadalupe Co., Pecos R. 3 mi. N. Dilia, 1958; UMMZ 94897 (146), Pecos R. at San Tuan, 1926; UMMZ 94898 (1), Pecos R. at San Juan, 1926; UMMZ 118209 (68), Sapello Cr. at Sapello, 1937; UMMZ 133131 (7), Pecos R. 0.5 mi. N Santa Rosa, 1940; UMMZ 133136 (1), Rio Grande at Albuquerque, 1940.

OKLAHOMA: KU 2329 (1), Cleveland Co.-McClain Co. line, S. Canadian R., 1952; UOMZ 26355 (10), Cimarron Co., Cimarron R. 2 mi. N. Kenton, 1957; UOMZ 5917 (2), Cleveland Co., S. Canadian R. S Norman, 1925.

TEXAS: KU 3409 (18), Hemphill Co., Canadian R. at town of Canadian, 1955.

WYOMING: WU 2084 (4), Platte Co., N. Platte R. at Glendo, 1956; WU 2095 (3), Converse Co., N. Platte R. at Douglas, 1956; UMMZ 104064 (58), N. Platte R. below Guernsey Dam, 1937; * UMMZ 114642 (7), drainage ditch in Wind R. drainage, 1936; * UMMZ 114644 (20), drainage ditch at Riverton, 1936; * UMMZ 127518 (63), Weston Co., Beaver Cr., 1934; * UMMZ 127681 (20), Big Horn Co., Big Horn R. tributary, 1939; * UMMZ 136488 (9), Crook Co., Belle Fourche R. 15 mi. N Devil's Tower, 1941; * WU 2122 and two uncatalogued series at WU (13), Belle Fourche R., no precise locality or date; UMMZ 159969 (14), Natrona Co., N. Platte R. 2 mi. E Casper, 1950.

INTRASPECIFIC VARIATION

Two subspecies of H. gracilis are recognized by us: one northern and eastern, characteristically inhabiting large rivers (H. g. gracilis), and one southern and western, characteristically inhabiting small streams (H. g. gulonella). Other scientific names that have been applied to this fish in the past are listed in the synonymy.

H. g. gulonella is a chubby, deep-bodied fish, whereas H. g. gracilis is long and slender. The head of the creek subspecies is deeper and longer than that of H. g. gracilis, being rounded anteriorly when seen in sideview. The head of the large-river subspecies is acutely wedge-shaped in profile. H. g. gracilis has a larger orbit than H. g. gulonella. Fins of H. g. gracilis are more strongly falcate than those of the other subspecies. H. g. gracilis has a greater number of lateral line scales, pectoral rays and post-Weberian vertebrae than the creek subspecies. The large-river subspecies attains much larger size than does the creek subspecies (Plate 24). Except in areas of intergradation, complete separation of the two subspecies can be made on the basis of lateral line scales, pectoral rays, post-Weberian vertebrae and head-depth. The regressions of head-depth on standard length in H. g. gracilis from the Saskatchewan River (several localities) and in H. g. gulonella from Beaver Creek, Arkansas River Drainage (KU 4769) are shown in Plate 24. Although values for the largest specimens of H. g. gracilis are omitted from Plate 24, the regression remains essentially linear to standard lengths of approximately 250 mm. On the basis of head-depth alone, separation of the two subspecies is possible in specimens larger than 40 mm. Similar results were obtained by using the regression of postorbital length on standard length, and could have been obtained by using other proportional measurements.

NATURAL HISTORY

Habitat

The species inhabits alkaline streams with shifting sand bottoms where the waterlevel fluctuates considerably with heavy rains and melting snow. The flathead chub is found in silty water and often is the predominant species in streams that have high turbidity. The remarkable ability of this fish to withstand exceedingly high turbidity is illustrated by its predominance in the Little Missouri River, which has an average concentration of suspended silt two and one-half times that of the Missouri River at Kansas City (Personius and Eddy, 1955:42).

H. g. gracilis is found in large rivers throughout its range, occasionally migrating into smaller streams, especially in the spawning season. It prefers the main channel of rivers in moderate to strong current. All series examined are from elevations lower than 3,000 feet.

Numbers to left of symbols = number of specimens examined from that locality; combined collections indicated by brackets. The dash-lines represent drainage patterns of rivers in which this species occurs.]

H. g. gulonella occupies small rivers and creeks, preferring pools with moderate currents. In fall, dense concentrations of this subspecies have been found in small pools, where brush, driftwood or other debris deflects the current and prevents filling with drifting sand. Hundreds of flathead chubs were collected in such pools in the Purgatoire and Arkansas rivers. Specimens were also collected with ease in Beaver Creek, Colorado, from pools with murky water and slight flow, over bottoms of gravel and bedrock. No brush or other debris was near the pools. In each case the streams carried little water, although they undoubtedly carry greater volumes of water in spring and early summer after rains and spring thaws. The preferred bottom-type for this subspecies seems to be gently shifting sand.

H. g. gulonella is found in warm-water streams, whereas H. g. gracilis occurs in cooler water. The southwestern subspecies was taken in August in the Mora River drainage at Sapello (temperatures above 80 deg. F.) but not at Mora (temperatures below 70 deg. F.). In the Purgatoire River, a thriving population was found where the water temperature was 92 deg. F., on September 6, 1959. In the Arkansas and Pecos rivers and the Rio Grande this subspecies is most abundant below the mountainous parts of the stream-courses, but at elevations higher than 4,000 feet on the plains.

Associated Species