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MOVEMENTS OF COLORADO SQUA WFISH 1043 TABLE 4. -Collections of ripe fish and presence of radio-tagged fish on spawning grounds, and estimated spawning period of Colorado squawfish in the Green and Yampa rivers, 1981-1988. Spawning period includes all indication of spawning activity, that is, dates when ripe fish and migrating, radio-tagged fish were present. Spawning period Fish presence Number Year Annual flow" Ripe Radio-taggedb Range of days Green River, Gray Canyon 1981 Low Jul2-Jul15 " 1982 Ave. Jull4-Jul 22 Jun 22-Aug 18 Jun 22-Aug 18 57 1983 High Aug 2-Aug 18 Jull8-Aug 16 Jull8-Aug 18 32 1984 High Jull2-Aug 16 Jul13-Aug 12 Jull2-Aug 16 36 1985 High Jun 30-Jul 21 Jun 28-Jul 20 Jun 28-Jul 21 24 1986 High Jul 9-Aug 7 1987 Ave. Jun ll-Jull5 Jun 17-Jun 30 Jun ll-Jull5 35 1988 Low Jul 6-Jul21 Yampa River, Yampa Canyon 1981 Low JulI-Jul10 Jun 20-Jul 20 Jun 20-Jul 20 31 1983 High Jull4-Aug 18 Jul12-Aug 8 Jull2-Aug ]8 38 1984 High Jul 18-Aug 14 JullO-Aug 17 JullO-Aug 17 39 1985 High Jun 27-Jul 25 Jun 21-Jul12 Jun 21-Jul 25 35 1988 Ave. Jun 29-Jul 6 Jun 20-Jul 24 Jun 20-Jul 24 35 "Designation based on mean annual flow. Ranges of means: Yampa River, 43-78 ml/s; Green River, 95-165 ml/s. Ave. = average flow. b Dates represent first and last appearance of radio-tagged fish on spawning grounds. Migratory radio-tagged fish and fish captured ripe on the spawning grounds were usually mon- itored or recaptured in upstream locations. Col- orado squawfish stocks above and below the spawning areas were different in length composi- tion. Of 76 electrofishing captures above Yampa Canyon (RK 74), the average total length of the fish was 566 mm (range, 380-774 mm) and only 5% (N= 4) were of juvenile size (<435 mm). The few juveniles taken in the upper Yampa River averaged 406 mm (range, 38~20 mm, N = 4). In the lower Green River (RK 35-149), average fish size was only 374 mm (range, 81-720 mm), and juvenile-size fish constituted 75% of the total (N = 84). Discussion Colorado squawfish began spawning migrations as spring water flows were decreasing and water temperatures were increasing, and they spawned TABLE 5.-Environmental conditions in the Green and Yampa rivers during spawning periods of Colorado squawfish, 1981-1988. Discharge (ml/s)b Water temperature ("C)C Year Spawning period" Mean Range Mean Range Green River 1982 Jun 22-Aug 18 237 99-461 23.1 19.5-27.5 1983 Jull8-Aug 18 362 224-518 22.5 20.0-25.0 1984 Jull2-Aug 16 282 205-393 21.9 20.5-23.0 1985 Jun 28-Jul 21 187 151-252 25.3 21.0-27.0 1987 Jun ll-Jull5 131 79-237 24.1 20.5-26.0 Mean 237 23.4 Yampa River 1981 Jun 20-Jul 20 25 12-45 18.0-25.5 1983 Jull2-Aug 18 82 29-197 18.0-27.0 1984 JullO-Aug 17 86 27-233 20.0-25.0 1985 Jun 21-Jul 25 69 28-152 14.5-25.5 1988 Jun 20-Jul 24 54 9-160 17.0-26.0 Mean 63 " Derived from contact with radio-tagged adults and collection of ripe fish on spawning grounds. b U.S. Geological Survey flow records (Green River, Utah, and Deerlodge Park, Colorado, stations) for daily discharges. C U.S. Geological Survey records for Green River, Utah, station. Yampa River data were taken in spawning reach with hand- held thermometers.