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Results and Discussion Distribution and Abundance River-wide catch rates were fairly high in all four rivers during 1993 compared with most years of ISMP data (Figures 9, 10, 11, 12; Table B-1). Mean CPE declined somewhat in the Colorado and Green rivers, but river-wide catch rates were still the second and third highest values (respectively) observed in the two rivers since ISMP began. Mean CPE in the Yampa River was the second highest value observed since monitoring began in 1986; however, it was only slightly higher than observed in 1991 and 1992. In the White River, mean CPE was the highest value observed since monitoring began. However, the last 5 years of data have been very comparable (McAda et al. 1994). In general, the sustained high catch rates in all four rivers suggest more subadult and adult Colorado squawfish in the upper basin than when the monitoring program began. Size Distribution The size distribution in the Green and Colorado rivers continues to reflect a large group of subadult fish that are nearing adult size (Figure 13; Table B-2, B-3). Using 5-cm length groups, the highest percentage of fish collected in the Green and Colorado rivers were between 35 and 40 cm long. Size distributions of Colorado squawfish from both rivers also indicate a substantial number of smaller fish as well. The median length of all fish collected from both rivers has been steadily increasing as a large cohort produced in 1986 has been growing in length (Figures B-1, B-2) and preparing to enter the adult population. Most fish collected from the Yampa and White rivers are adults, but both rivers also contain a high percentage of subadult and young adult-size fish. Size distributions and median length of fish collected from these two rivers have been relatively constant since ISMP began (Figures B-3, B-4). This constant size distribution suggests slow, but regular recruitment into the adult populations of the two rivers and the entire upper basin. SymQatric Species Native Species-Razorback sucker Xyrauchen texanus was only collected from Reach 3 in the Green River (Table B-4). Three individuals were captured there, compared with two individuals in 1992 and three in 1991. Twelve or more razorbacks were collected from the Green River during ISMP sampling from 1986-1990 (McAda et al. 1994). Two humpback chubs and six roundtail chubs were collected from the Colorado River in Utah (Table B-4). One roundtail chub was collected from the Green River. Roundtail chubs are common in the rivers in Colorado sampled during ISMP and are not recorded by the collecting crews. Introduced Species-Northern pike Esox lucius continued to be observed in relatively high numbers in the Yampa and upper Green Rivers (Table B~). A total of 23 northern pike were observed in the upper Green and 29 were observed in the Yampa River. These numbers compare with nine in the Green and 70 in the Yampa during 1992. Twenty-six smallmouth bass Micropterus dolomieui were collected from the Green River and 14 were col[ected from the Yampa River (Table B-4). These values reflect a decrease from higher numbers of bass observed in earlier years of ISMP (McAda et al. 1994). 11