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MOVEMENTS OF COLORADO SQUAWFlSH 1041 TABLE 2. - Spawning collections of Colorado squawfish in the Yampa and Green rivers, June-August 1981-1988. N = all squawfish captured on spawning grounds; n = sample size; TL = mean total length in mm. "Suspected" means fish were not ripe but were judged to be in breeding condition. Males Females Ripe Suspected" Ripe Suspectedb Year River N n TL n TL n TL n TL 1981 Yampa 35 20 538 6 528 I 779 2 748 Green 4 I 478 0 0 0 ... 1982 0 Yampa I I 547 0 0 Green 11 6 509 0 0 2 642 1983 Yampa 22 13 596 I 560 3 722 2 662 Green 14 11 569 0 0 I 625 1984 Yampa 38 20 560 I 510 3 666 11 714 Green 29 14 574 4 544 I 750 6 671 1985 Yampa 13 10 571 0 I 723 I 639 Green 36 24 574 5 549 0 2 626 1986 Yampa 12 7 535 0 I 485 3 702 Green 24 22 541 I 559 0 I 781 1987 Yampa 19 13 539 I 510 0 4 621 Green 25 16 533 4 520 0 4 666 1988 Yampa 5 4 544 0 0 I 725 Green 20 12 563 2 588 4 565 2 684 All Yampa 145 88 556 9 530 9 683 24 693 Green 163 106 555 16 546 5 602 18 667 " Heavily tubercu1ated and colored fish with no expressible sex products. b Large fish with little coloration, little or no tuberculation, large vent, and no expressible sex products. River spawning reach 2 weeks after it had been collected there when ripe. This fish was subse- quently tracked to the upper Yampa River (RK 160), where it had been radio-tagged in the spring. Adult-size Colorado squawfish (~500 mm) dis- played breeding colors and were sexually dimor- phic. In late winter and early spring, fish were light silver in general body color. In summer, ripe males were bronze-colored, with robust breeding tuber- cles on fins and body. Ripe females were lighter in color, with few or no small tubercles on the dorsal surface of the head and back. Ripe females did not have tubercles on paired fins. Ninety unripe fish were captured on the spawn- ing areas in summer. Of these, fish with bright coloration and robust tubercles on the body and fins were classified as suspected males (N = 25). Large fish with lighter coloration, little or no tu- berculation, and large vents (N = 42) were clas- sified as suspected females. Sex of the remaining 23 fish was not determined. Average total length of ripe male Colorado squawfish (554.9 mm; range, 435-725 mm) was significantly less than that of ripe females (654 mm; range, 485-820 mm; Student's t, P < 0.05). Ripe males were more abundant in the spawning collections than ripe females; the male: female ra- tio was 14.9: 1. However, when all fish in breeding condition were included, a ratio of 5: 1 resulted. Ripe fish were collected on the Green and Yam- pa spawning grounds in areas occupied by radio- tagged fish in all years. Numerous capture loca- tions of ripe fish and behavior of radio-tagged fish suggested that egg deposition and fertilization were concentrated in relatively small river reaches (<20 kID) where large, deep pools, eddies, and sub- merged bars of cobble, gravel, boulder, and sand substrates were associated with the main channel. However, substrates in the two spawning reaches were different. Substrates in Yampa Canyon were dominated by imbricated cobbles intermingled with gravel and sand. In the Green River, sub- strates were boulders, sand, and silt. Although high turbidity precluded direct observation of fish or deposited sex products, the signal source of radio- tagged fish indicated that fish rested or staged in pools or eddies (average depth, 2 m; average ve- locity, 0.3 m/s) for hours or days, and moved abruptly to nearby cobble or boulder bars (average depth, 1.0 m; average velocity, 0.6 mis, Table 3), where they remained from 30 min to 3 hand presumably spawned before returning to their for- mer habitats. A fidelity to one spawning area was noted in