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SPAWNING MOVEMENTS OF COLORADO SQUAWFISH
<br />reach occupied for the longest time was consid-
<br />ered the spawning reach. Because we were pri-
<br />marily interested in the spawning movements of
<br />Colorado squawfish, fish not contacted during both
<br />the estimated spawning period and the subsequent
<br />postspawning period were excluded from analy-
<br />ses.
<br />Larval Fish
<br />Results
<br />Altogether, 131 larval Colorado squawfish were
<br />collected in 1982, 37 in 1983, 46 in 1984, and 108
<br />in 1985. They represented 0.9, 0.5, 0.4, and 0.9%
<br />of all fish larvae collected in these years. Colorado
<br />squawfish larvae occurred in 18% of the collec-
<br />tions in 1982, 6% in 1983, 8% in 1984, and 14%
<br />in 1985. They were first collected in mid-July 1982
<br />and 1984, in late July 1985, and in early August
<br />1983. Larvae were distributed among reaches 1-
<br />6 in all years except 1983, when they were found
<br />in only four reaches (Table 1). Colorado squawfish
<br />larvae of two size-classes (6-10 and 11-21 mm
<br />TL) were found in each of the study reaches except
<br />7 and 8. No Colorado squawfish larvae were col-
<br />lected from reach 8, and larvae were found in reach
<br />7 only in 1982. Within study reaches and years,
<br />capture of 11-21-mm Colorado squawfish larvae
<br />was most often accompanied by the capture of 6-
<br />10-mm larvae (15 of 22 cases). The seven cases
<br />in which this association did not occur were even-
<br />ly divided among the seven study reaches and thus
<br />showed no consistent pattern among years (Table
<br />1).
<br />Spawning Dates
<br />Estimated onset of spawning in the lower river
<br />reaches (1, 2, and 3) was late June 1985, early July
<br />1982 and 1984, and late July 1983 (Table 2).
<br />Spawning continued into early August in 1982 and
<br />1985 and into early September in 1983 and 1984.
<br />Spawning in reaches 6 and 7 began in late June
<br />1985, mid-July 1982 and 1984, and mid-August
<br />in 1983. Spawning in reaches 6 and 7 began when
<br />seasonal river temperature at the state-line gauge
<br />reached 18-22°C, water level was decreasing, and
<br />streamflows were 15-30% of the maximum dis-
<br />charge for that year.
<br />Movement of Radio-Tagged Fish
<br />We implanted radio transmitters in 74 adult
<br />Colorado squawfish during the study: 22 in 1982,
<br />21 in 1983, 13 in 1984, and 18 in 1985. Eleven
<br />fish were tagged with 18-month transmitters in
<br />341
<br />early fall 1982 and the rest with 6- or 10-month
<br />transmitters in early spring 1982-1985. Our cri-
<br />terion for radio contact during and after the esti-
<br />mated spawning period was met by 50 fish: 7 tagged
<br />in reach 1, 13 in reach 3, 1 in reach 4, 2 in reach
<br />5, 20 in reach 6, 4 in reach 7, and 3 in reach 8
<br />(Table 3). Total number of contacts per fish ranged
<br />from 2 to 28 (mean, 10.2). Among those fish ex-
<br />cluded from analyses were three individuals that
<br />either died or expelled their transmitters.
<br />There was no significant difference (P > 0.05)
<br />in spawning displacement, maximum displace-
<br />ment, or final displacement of radio-tagged Col-
<br />orado squawfish among either the river reaches
<br />(Table 3) or 100-mm length-classes of fish. There
<br />was no significant difference (P > 0.05) among
<br />displacement types either riverwide or within
<br />reaches. The two fish (500-600 mm TL) that
<br />moved the longest distances (313.0 and 193.4 km)
<br />were tagged in the lower river (reaches 1 and 3).
<br />Maximum fish displacement ranged from 1 to 313
<br />km (mean, 38.1 km); displacements were distrib-
<br />uted as follows: 1-10 km, 12 fish; 10.1-20 km, 10
<br />fish; 20.1-30 km, 4 fish; 30.1-40 km, 7 fish; 40.1-
<br />50 km, 11 fish; 50.1-100 km, 4 fish; greater than
<br />100 km, 2 fish. Although not included in our study
<br />area, the lower Dolores and Green rivers (Figure
<br />1) were searched by aircraft on several occasions;
<br />no radio-tagged Colorado squawfish were found
<br />there.
<br />Of the 50 fish successfully radio-tracked during
<br />the estimated spawning season, 30 were in the
<br />reach of release and 20 had moved to adjacent
<br />reaches, where they remained for most of the
<br />spawning season. Ten fish occupied more than one
<br />reach during the estimated spawning season. Of
<br />the 20 fish that occupied an adjacent reach during
<br />most of the spawning season, 10 later returned to
<br />their original reach and 10 remained in the adja-
<br />cent reach at the time of last radio contact. Four
<br />fish left the reach of release after the estimated
<br />spawning period. Spawning displacements ranged
<br />from 0 to 92.7 km (mean, 23.2 km): 0-10 km, 21
<br />fish; 10.1-20 km, 8 fish; 20.1-30 km, 6 fish; 30.1-
<br />40 km, 3 fish; 40.1-50 km, 7 fish; 50.1-60 km, 2
<br />fish; 80.1-90 km, 1 fish; 90.1-100 km, 2 fish. Of
<br />the 50 fish with which radio contact was main-
<br />tained into the postspawning period, 72% were in
<br />their reach of release at the time of last contact
<br />and 52% were within 8 km of the release point.
<br />Seven Colorado squawfish radio-tagged in
<br />reaches 6 and 7 were located in a 5-km segment
<br />of reach 7 (RK 281-286) during the estimated
<br />spawning period in 1982. Three of these fish oc-
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