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7 Table 6. Percentage of fish of different species in collections made with trammel nets at stations 4, 5, 6, and 7, Green River, Utah, on different dates in 1974-75, and (for 9-10 December and 13-15 April) catch per unit of effort (CPE).e (See Fig. 1 for locations of stations.) _ Year, stations, dates, and (in parentheses) total number of fish caught on those dates 1974 1975 Sand Wash Ouray Horseshoe Bend (station 7) (station 6) Island Park (station 4) (station 5) 9-10 Dec. 13-15 April (103) 5-8 Dec (61) 2-4 Oct. 6-9 Oct. Speciesb Percent CPEe (22) Percent CPEa (129) (42) Catostomus latipinnis (N) 52.4 10.2 95.0 65.6 0.40 27.1 45.3 C. discobolus (N) - - - 19.7 0.10 57.4 14.3 C. commersoni - - - 1.6 0.01 2.3 - Xyrauchen texanus (N) 1.0 0.1 - 3.3 0.02 0.8 - Cyprinus carpio 34.0 8.6 - - - 3.9 21.4 Ptychocheilus Lucius (N- 1.9 0.11 - - - 0.8 4.8 2.3 Gila robusta (N) - - - - - 2.4 Ictalurus punctatus 10.7 2.3 5.0 1.6 0.01 2.3 4.8 Salmo gairdneri - - - 6.6 0.04 1.6 - S. trutta - - - 1.5 0.01 1.6 - Stizastedion uitreum - - - - - - 4.8 Micropterus dolomieui - - - - - - 2.4 aCPE =catch per unit effort; 1 unit of effort = 10 m of,net (2.1 m deep) set for 10 h. bN =native species. throughout the year. Even though introduced fish composed most of the catch in the gravel pit, the - flannelmouth sucker was still the most abundant species. Carp (Cyprinus carpio), green sunfish (Lepo- mis cyanellus) and black bullheads (Ictalurus melas) had become well established and together made up nearly a third of the total catch. Razorback suckers were less common in the Colo- rado River tlian in the gravel pit. A sample taken by electrofishing in the Colorado River (near station 8) in spring 1975 contained 127 flannelmouth suckers, 109 bluehead suckers, and 1 razorback sucker. Another collection, at the mouth of the Gunnison River (sta- tion 9) in April 1976, yielded 96 flannelmouth suckers and 86 bluehead suckers, but no razorback suckers. Only a few razorback suckers were collected at other locations in the basin (Table 6). A single razorback sucker was collected in December 1974 at station 7, and two in April and one in October 1975 at station 4. None were collected at stations 1, 2, 5, or 6. The ab- sence of razorback suckers in collections from the upper Yampa River (stations 1 and 2; Table 3) prob- ably indicated that they were rare in this section of the river. However, their status at stations 5 and 6 is uncertain because only one collection was made at each locality. Razorback suckers were common near station 6 in May 1978 (P. B. Holden,. personal com- munication), when they were concentrated in a large eddy near the mouth of the Duchesne River. Other razorback suckers were found above station 5 and below station 6 during the same period (D. Robinson, personal communication). In general this species is found in the Green River from its confluence with the Colorado River upstream to its confluence with the Yampa River (Fig. 2-. Age and Growth Growth Scales from all razorback suckers were removed from a key area midway between the lateral line and the origin of the dorsal fin. We made scale impressions on cellulose acetate cards (7.5 cm x 12.5 cm x 0.05 mm), using heat and pressure. The impressions were magnified 80x on an Eberbach no. 2700 projector. The scales of each fish were read twice. If the readings agreed, the age was accepted. If the two readings did not agree, the scale was examined a third time, and an age assigned on the basis of the agreement of the third reading with one of the first two. Most razorback sucker scales were difficult to read. The annuli were often indistinct and difficult to locate. Closely spaced circuli and the "cutting over" of circuli in the lateral fields were the characteristics used to determine the location of annuli. Scales from the key