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Table 5. Earliest dates of spawning-related water temperatures, Colorado and Yampa river study area, 1979-83 (U.S.G.S. Data). Records were unavailable for 17 Apr - 21 Jul 1980. Colorado Rivera Yampa Riverb 1979 1980 1981 1982 1980 1981 1982 Maximum >18 C 29 Jun 25 Jun 10 Apr 27 Jun 19 Jun 28 Jun 18 C + 30 days 28 Jul 24 Jul 10 May 26 Jul 18 Jul 28 Jul Maximum >20 C 12 Jul 26 Jun 28 May 9 Jul 20 Jun 9 Jul Maximum >22 C 22 Jul 30 Jun 20 Jun 18 Jul ~ 24 Jun 15 Jul Earliest estimated 29 Jun 28 Jun 18 Jun 10 Jul ~ 16 Jun 25 Jun 6 Jul spawning date aRecords at Colorado-U tah line. b Records at Maybell, C olorado (Moffat Co .) with exc eption of 198 2 which ~•~ere recorded at Deerl odge Park, Dinosaur National Monument. Drift Net Collections The 258 specimens collected in 61 drift samples (48 in the Colorado River and 13 in the Yampa River) were predominantly larvae (juvenile and adult forms comprised <3%) and represented 12 species and 4 families (Table 6). Of the 12 species, 6 were native and comprised 77% of the total ichthyoplankton sampled in 1982. A total of 118 specimens was collected in the Colorado River study area, representing 10 species and 4 families. Bluehead suckers (Catostomus discobolus), speckled dace (Rhinichthys osculus), and unidentified chubs (Gila spp) were the predominant native species, constituting 29, 27, and 25% of the total catch, respectively. The channel catfish (Ictalurus punctatus) was the most abundant non-native species, comprising 6% of the total. Notably, 2 larval Colorado squawfish were collected in the Colorado River study site on 27 July (Table 7). Although larvae of this endangered species have been taken on a number of occasions with fine-mesh seines and dipnets (Wick et al. 1981, Haynes and Muth 1982) this was the 1st drift-net collection of larval Colorado squawfish throughout the entire upper Colorado River basin.