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i 74 Colorado River basin and thus the major sub- jects of this report, have been caught be- tween 1974 and 1988 downstream from Lake Havasu. All but one were from the extensive system of artificial waterways that have been constructed for irrigated agriculture. In Arizona, canals near Parker produced two fish (32.3 and 37.1 cm TL) in 1980, two specimens (each 30 cm) in 1981, and four aver- aging 35.2 cm in 1986 (Minckley 1983, Ulmer and Anderson 1985, S. Yess, USFWS, per- sonal communication). Intake of water for the Parker area canal system is at Headgate Rock Dam, about 23 km downstream from Parker Dam. In California, one specimen (23.4 cm) was angled from a canal east of Palo Verde in 1983, which obtains its water from Palo Verde Diversion Dam, 21 km upstream from Blythe. Farther south, in Imperial Valley, the Coa- chella Canal (Fig. 1), its laterals, and its equal- izing reservoirs produced three fish (average 34.8 cm TL) in 1984, and four others averag- ing 35.5 cm in April 1985 (Ulmer and Ander- son 1985). Five young (---15 cm TL) were taken in 1973 and 1974 from the East Highline canal and adjacent ponds at Niland (St. Amant et al. 1974), a single fish measuring 22.5 cm fork length (FL x 1.085 ± 0.021 = 24.4 cm TL; unpublished data) was taken from the canal at Niland in 1974 (Ulmer and Anderson 1985), and another ---30.5 cm long was cap- tured there from a canal-fed pond in Decem- ber 1985 (E. Milstead, Niland, California, personal communication). Intake of water for the Imperial Valley is mostly through the All- American Canal, which originates near Impe- rial Dam (Fig. 1). The only small fish from the mainstem Colorado was a 35.1-cm individual captured 16 km downstream from Parker, Ari- zona, between Headgate Rock and Palo Verde Diversion dams, in summer 1987 (Langhorst 1988). That specimen was two years of age by otolith examination. Assuming all these juvenile fish exhibited growth rates similar to those from Lake Mo- have, hatchery ponds (McCarthy and Minck- ley 1987), and a variety of other waters where reintroduced populations have been studied (Marsh, in press, Marsh and Minckley, un- published data), none was more than five years old. Only the eight fish captured in 1983 or later (three fish in 1984 and five others in 1985) from canals and other waters confluent with the All-American Canal (Fig. 1) could GREAT BASIN NATURALIST Vol. 49, No. 1 have been derived via West Pond from artifi- cially propagated stocks (see below); all others were wild fish. Reintroductions, 1980-88 The first razorback sucker reintroduction to the lower Colorado River area was in 1980. It consisted of 17 hatchery-produced adults (average 32.5 cm TL; 1974 year class, Toney 1974) and 3 Lake Mohave adults (average 56.6 cm TL, ages unknown) into the isolated West Pond, Imperial County, California (Fig. 1; W. Loudermilk, CADFG, personal commu- nication). An unknown number of progeny of Senator Wash Reservoir fish, artificially prop- agated and reared by CADFG personnel, also were stocked in West Pond between 1981 and 1983 (L. Ulmer, CADFG, personal communi- cation). In November 1983, 457 razorback sucker juveniles (average 95 mm TL) from Lake Mohave broodstock also were stocked into an artificial rearing enclosure constructed in West Pond by USBR; samples of those fish averaged 115 mm (N = 5) in December 1983 and 156 mm (N = 5) in January 1984 (Ulmer, personal communication). West Pond and the enclosure were not again monitored until 1988, when no razorback suckers were en- countered. Because water from West Pond is pumped into the All-American Canal, these stocked fish could have contributed to the eight post- 1983 juvenile occurrences downstream in the confluent Coachella and East Highline canals or their adjacent ponds and reservoirs. Fur- thermore, progeny of Senator Wash Reservoir adults, artificially propagated in spring 1983, were also reared in aquaria in Blythe, Califor- nia, and later transferred for grow-out in local ponds. A total of 57 survivors (average 28.5 cm TL for 39 measured) was stocked into the Colorado River mainstem near Blythe in April 1985 (Ulmer, personal communication). A dozen others (unmeasured) from the same group were stocked into an isolated pond on federal lands in February 1986 (Ulmer, per- sonal communication). These last two stock- ings could not have contributed to subsequent captures from the areas of Parker, Arizona, or Palo Verde, California, because they were downstream from barriers created by Head- gate Rock and Palo Verde Diversion dams (Fig. 1); however, fish could have made their way downstream to Imperial Valley.