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294 .ii The Southwestern Naturalist vol. 29, no. 3 August 1984 Tyus and McAda-SquawCish Movements 295 TA8L~ 2._Recapture of Colorado squawfish tagged with dangler tags on spawning grounds, Yampa River, 1981. I PREs"j"'"G I".' I Yampa Yampa Yampa Yampa 5 27 26 28 560 607 506 510 66 120 62 2 '.w 200 CapLUft" Fish No. Dall' Riv('l l.o('atiorl(km)ITL(mm) Date 326G 05-27 -81 Green 491 560 06-\8-81 1027Y' 10-08-80 Yampa 147 593 07 -09-8\ \537 B/W' 08-21-78 Yampa 88 452 07-05-81 1313Y 08-07 -8\ Yampa 26 510 07-08-81 Rec:apwre River LCK"3lion(km) TL(mm Distance? IMouth of river;:: 0 km 1Givell from pOlnlll{ caplur{' to point of recapLUft' ]Tag~ed by colorado Division of Wildlife q"aJitged by Blowesl, Inc, Logan. Utah ..J c( > ffi 400 I- ~ ....... 200 ::i! POST - period. Therefore, it is important to consider the. res.ult~ of larval fish collections conducted by the Colorado Division of WIldlife I? August 1980, and the more intensive sampling by the CDOW and FWS.m July-August 1981. The 1980 collections produced larval Colorado squawhsh 10 the lo~er 16 km of the Yampa River. Although the lower 190 km ~f the Yampa RIver was intensively sampled in 198 I, larval Colorado squawhsh (9- I 3 mm) w.ere collected only in the lower 20 km. This is supportive proof that. spawn~ng is restricted to the lower 32 km as suggested by hsh behavlOr dunng radiotelemetry, the collections of ripe fish, and the distribution of larvae. . Most of the movement by Colorado squawfish in the Green a~d W~ue rivers also occurred in June and July and was linked with spawn~n.g smce sedentary fish were apparently immature. Highe~ ~ater con~ucuvuy and larger river conditions made radiotrac~ing mor.e dIfhcult and.u was harder to maintain radio contact with the hsh. Dunng the spawmng s~ason. of 1980 and 1981, two fish tagged in the Green and one in the Whue RIVer (Table 1) displayed a highly mobile movement pattern that suggested spawning migration in addition to the fish that migrated f~om the G~een River to the Yampa River spawning grounds. Two of these hsh moved mto Gray Canyon and one moved into Split Mountain ~anyon. .Both of these areas are similar in habitat conditions to the spawmng area 10 the Yampa Canyon, and the fish could have spawned there. .' . Short-term, local movements of Colorado squawfish weremvesugated by diel studies. No clear pattern emerged when data were lumpe~ for the ye~r. The data were then partitioned into three periods: prespaw~mg (15 Apnl- 15 June), spawning (16 June-15 July), and posts~awmng (16 Jul.y-I October). There was no diel rhythm apparent unul the postspawmng period, when activity peaked between 0800-1200 h (Fig. ~). . Habitat Preferences.-Colorado squawfish were momtored predomI~atelY in shoreline habitats and were associated with sandy subst~ate (FIg. .4); however, they also used eddy, run, backwater, and pool habnats and s~lt, boulder, rubble, and gravel substrates. Habitat and substrat:. use vaned between river system and time of year. Water depths and veloClues recorded at observed locations of Colordo squawfish indicated the fish selected depths and velocities averaging 1.4 m and 0.2 m/s for the Green River, 0..9 m ~nd 0.1 m/s in the Yampa River and 0.7 m and 0.5 m/s in the Whue RIver 2400 0400 0800 1200 1600 2000 2400 TIME INTERVAL MOVEMENT FIG. 3.-Movement oC Colorado squa.wfish, die! studies, Green, While and Yampa rivers, 1980- 81. n 0= number DC 15 minute observations. respectively. An Analysis of Variance for water depths and velocities (Table 3) recorded at observed locations of radiotagged Colorado squawfish indicated a significant difference (p = 0.01) in depths and velocities recorded between the Green, White and Yampa rivers. There was no difference between the water depths and velocities recorded between 1980 and 1981 in the Green River: however, it is not known whether Colorado squawfish selected different conditions between river systems or were able to tolerate the wide range of conditions present between the Green River mainstem and its two tributaries the White and Yampa rivers. A physical characterization of sparning habitat was made in the Yampa River at km 26.4. This location was selected after tracking radiotagged Colorado squawfish back and forth from pool to riffle habitat and after collecting 13 ripe Colorado squaw fish in one net haul. No visual observation could be made because of high turbidity. Noon temperature was 22 C and water discharge was in the descending limb of the hydrograph. Water depths and velocities ranged from 0.9-2.1 m and 0 to 0.1 m/s respectively. Substrate was cobble averaging 8 em diameter over the bars, with bedrock/sand in the pools. Young-of-the-year Colorado squawfish are relatively absent in the Yampa River after the spawning season but are common in the Green River below the mouth of the Yampa. It appears that the larvae are transported out of the spawning area to more suitable nursery habitat in the Green River. The nursery habitats utilized in the Green River are shallow ephemeral backwaters with silt/substrates that are rich in food organisms. This type of habitat is rare in the Yampa Canyon.