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70 Razorback suckers now spawn in lap-zone gravel substrates of reservoirs in the lower basin, but eggs are subjected to longer incubation times, wave action distur- bance, greater predation and dessication with water level fluctuations. As you move downstream to the Gulf, the water temperatures come closer to the suspected desirable range for egg maturation, but spawning substrates are not available there. Not enough information exists to discuss problems involving the larval stage. HYBRIDIZATION Another aspect to consider is hybridization with other suckers of the genus Catostomus. Hubbs and Miller (1953) clarified the identification of a specimen, collected.in the Uncompahgre River near Delta, Colorado in 1889, as a flannelmouth x razorback sucker hybrid (C. Zatipinnis x X. texanus). They theorized that the abundance of flannelmouths relative to that of razorbacks and the close similar- ities in spawning requirements explained the natural hybridization occurring. Almost half of the razorbacks sampled in the Green River below Flaming Gorge Reservoir in 1967-1973 were flannelmouth x razorback hybrids (Vanicek, 1970; Vanicek et al., 1970; Holden 1973; Holden and Stalnaker, 1975; Behnke and Benson, 1980). Razorback sucker crosses with white suckers (X. texanus x C. commersoni) and bluehead suckers crossed with white sucker (C. discobotus x C. commersoni) were collected from the Yampa River, a tributary to the Green River below Flaming Gorge Dam, during the same time period (Holden, 1973), and flannelmouths were the dominant species there at the time. Flannelmouth sucker were reported downstream in the last major tributary to the lower Colorado River, the Gila River, near the confluence at Yuma in the late 1800's and have more recently been collected in Lake Mohave (W. L. Minckley, pers. comm.). Gustafson (1973) reported that a minimum of 10% hybridization between X. texanus and an undetermined species of Catostomus was indicated from data collected at Lake Mohave. Razorback x Gila sucker (X. texanus x C. insignis) hybrids were collected from Tonto Creek, Arizona in 1926 (Hubbs & Miller, 1953). This creek is a tributary to the Salt River, the Gila River and eventually the lower Colorado RjLver. Flannelmouth (C. Zatipinnis) a western white sucker (C. commersoni suekZeyi), the dusky mountain sucker (Pantosteus sp.), Bonneville mountain sucker (P. platyr- hunehus), Utah bluehead sucker (P. deZphinus), northern bluehead sucker (P. d. deZphinus) and the Rio Grande mountain sucker (P. pZebeius) were all used as bait fish in the lower Colorado River during the late 1940's and early 1950's (Miller, 1952). In 1976, approximately 600 adult flannelmouth sucker were transplanted into the mainstream of the lower river below Davis Dam (River Mile 276) near Bullhead City, Arizona (Minckley, 1973). What I have just described is that in mainstream tributaries of both the upper and lower basins where razorback range overlapped with abundant populations of flannelmouth (C. Zatipinnis) or Gila sucker (C. insignis) some degree of hybridiza- tion resulted. Hybrid introgression may help explain the gradual decline of razor- back populations. RECOVERY So how do we get them back? Reintroduction without defining and satisfying egg and larval survival requirements and not considering habitat maintenance will