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vol. 36, no. 1 March 1991 Notes
<br />149
<br />ADO
<br />Navajo Reservoir
<br />Z
<br />FARMINGTON
<br />KICO
<br />uan River, 1987 to 1989. Numerals
<br />Colorado squawfish, and stippling
<br />s indicate capture sites of razorback
<br />distributed from 4.4 km down-
<br />New Mexico, to Lake Powell,
<br />individual captured in the San
<br />f Lake Powell on 7 April 1987
<br />s subsequently recaptured on 8
<br />632 mm TL) during a night-
<br />; operation approximately 145
<br />t from the initial point of cap-
<br />tudy adult Colorado squawfish
<br />sighted in the San Juan River
<br />h month from April to October,
<br />1'ung-of-year (YOY) Colorado
<br />g in size from 17.2 to 39 mm
<br />in low velocity habitats in the
<br />San Juan River during 1987. Nine specimens
<br />were collected in the San Juan River inflow area
<br />near Lake Powell (river kilometers, RK, 0 to 24),
<br />one at RK 38.0, six close to the confluence of
<br />Montezuma Creek and the San Juan River (RK
<br />152.4 to 164.0), and two near the confluence of
<br />the San Juan and Mancos rivers (RK 225.0 to
<br />230.6). One YOY Colorado squawfish (19 mm
<br />TL), was collected in 1988 (RK 18.5) and none
<br />were taken in 1989. These were the first records
<br />of YOY Colorado squawfish in the San Juan
<br />River drainage.
<br />Between 20 March and 5 April 1987, we re-
<br />corded 18 adult razorback sucker captures (12
<br />individuals; six were recaptured once) along the
<br />south shore of Lake Powell near the concrete boat
<br />ramp at Piute Farms Marina, Utah. Eight males
<br />were ripe, had well-tuberculated anal and caudal
<br />fins, and expressed milt when mild external pres-
<br />sure was applied. Abdomens of females (n = 4)
<br />were distended and they appeared to be gravid.
<br />In 1988 (20 to 30 March), 10 adult razorback
<br />suckers, half of which were reproductively ma-
<br />ture (expressed milt or appeared gravid), were
<br />collected at the Piute Farms Marina boat ramp.
<br />Six of the 10 specimens were recaptures from the
<br />1987 sample. This concentration of fish suggested
<br />a spawning aggregation (Minckley, 1983; Tyus,
<br />1987) or staging prior to migration to another
<br />spawning site.
<br />On 25 April 1988, a ripe, tuberculate male
<br />razorback sucker (571 mm TL) was captured at
<br />RK 146.7 near Bluff, Utah. This was the first
<br />record of this species from the mainstream of the
<br />San Juan River. No larval razorback sucker were
<br />found in the 292 collections of larval fish during
<br />our survey.
<br />The rediscovery of adult Colorado squawfish,
<br />presence of several age classes, and documenta-
<br />tion of its successful spawning in the San Juan
<br />River reconfirmed the species as a viable com-
<br />ponent of the ichthyofauna of the San Juan River.
<br />The presence of razorback sucker in the mainstem
<br />of the San Juan River 147 river km upstream of
<br />Lake Powell verified its status as a member of
<br />the fish fauna of the San Juan River. The col-
<br />lection of a reproductively-active individual sug-
<br />gested that the species may be spawning in the
<br />riverine portion of the San Juan River. These
<br />findings reinforced the importance of the San Juan
<br />River drainage to the continued survival of these
<br />rare species. Additional studies are necessary to
<br />locate spawning sites and larval fish nursery ar-
<br />eas, determine population sizes, seasonal move-
<br />ment, and genetic stock, and define factors lim-
<br />iting these populations.
<br />This study was funded by the United States
<br />Bureau of Reclamation (USBR), Salt Lake City,
<br />Utah, through contracts to the New Mexico De-
<br />partment of Game and Fish, Utah Division of
<br />Wildlife Resources, United States Fish and Wild-
<br />life Service, and University of New Mexico. We
<br />thank, R. D. Williams (USBR) for administrat-
<br />ing these contracts, D. E. Snyder (Colorado State
<br />University Larval Fish Laboratory) for verifying
<br />identification of YOY Colorado squawfish, and
<br />the many individuals who assisted with the field-
<br />work. We are especially grateful for the coop-
<br />eration and assistance of the Navajo Nation. Col-
<br />lecting permits were provided by the Navajo
<br />Nation and United States Fish and Wildlife Ser-
<br />vice.
<br />LITERATURE CITED
<br />HOLDEN, P. B., AND E. J. WICK. 1982. Life history
<br />and prospects for recovery of Colorado squawfish.
<br />Pp. 98-108, in Fishes of the Upper Colorado River
<br />system: present and future (W. H. Miller et al.,
<br />eds.). Amer. Fish. Soc., Bethesda, Maryland, 131
<br />pp-
<br />JORDAN, D. S. 1891. Report of explorations in Col-
<br />orado and Utah during the summer of 1889, with
<br />an account of the fish found in each of the river
<br />basins examined. Bull. U.S. Fish Comm., 89:1-40.
<br />LANIGAN, S. H., AND H. M. Tyus. 1989. Population
<br />and status of the razorback sucker in the Green
<br />River Basin, Utah and Colorado. N. Amer. J. Fish.
<br />Mgmt., 9:68-73.
<br />MILLER, R. R. 1961. Man and the changing fish
<br />fauna of the American Southwest. Papers Michigan
<br />Acad. Sci., Arts, Letters, 46:365-404.
<br />MINCKLEY, C. O., AND S. W. CAROTHERS. 1979. Re-
<br />cent collections of the Colorado River squawfish
<br />and razorback sucker from the San Juan and Col-
<br />orado rivers in New Mexico and Arizona. South-
<br />western Nat., 24:686-687.
<br />MINCKLEY, W. L. 1973. Fishes of Arizona. Arizona
<br />Game Fish Dept., Phoenix, 293 pp.
<br />1983. Status of the razorback sucker, Xy-
<br />rauchen texanus (Abbott), in the Lower Colorado
<br />River Basin. Southwestern Nat., 28:165-187.
<br />Tyus, H. M. 1987. Distribution, reproduction, and
<br />habitat use of the razorback sucker in the Green
<br />River, Utah, 1979-1986. Trans. Amer. Fish. Soc.,
<br />116:111-116.
<br />Tyus, H. M., ET AL. 1982. Fishes of the Upper
<br />Colorado River Basin: distribution, abundance, and
<br />status. Pp. 12-70, in Fishes of the Upper Colorado
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