9375

• UCREFRP Catalog Number: 9375
• Author: Kimball, J. F.
• Title: Flow Effects on Humpback Chub ‎(Gila cypha)‎ in Westwater Canyon.
• USFW Year: 1999.
• USFW - Doc Type: Salt Lake City.
• Copyright Material: NO

Table 3. Days post hatch and back-calculated hatching dates for YOY chubs collected above and
within Westwater Canyon, Colorado, on selected dates in 1992, 1993, 1994 and 1996.
Modal peaks are from respective length frequency analyses.
ABOVE CANYON
Modal Peak Estimated
DATE (Std length (mm)) Davs Post Hatch Hatch Date
920721 18.6 28.7 920623
920721 29.4 43 920608
*930625 14.3 25.9 930531
930802 11.4 13.4 930720
930802 17.2 26 930707

940712
16.4
24.8 _
940717
960725 13.5 18.8 960706
WESTWATER CANYON
Modal Peak Estimated
DATE (Std length (mml) Davs Post Hatch Hatch Date
920721 15.7 23.4 920629
920721 20.8 32 920619
930802 14.3 20.3 930713
940712 14.9 22 940620
950905 24 29.9 950805
960725 14.3 20.4 960705
960815 23.6 36 960710
*seven fish collected on this date were spawned before the peak.Jlow in 1993 -this early spawning time is addressed in the
Discussion section.
There were strong correlations found between earliest hatching dates (modal peaks) and a) pre-
peak flow (>6000 cfs) days (r2=.9881)and b) pre-peak degree (>10°C) days (r2 = .9778(neg.)) in
Westwater Canyon, i.e., the more flow on the ascending limb of the hydrograph, the later chubs spawned.
These correlations were significant (p < 0.05) for the flow metrics and nearly significant (p = 0.087) for
temperature. A similar analysis of hatching times above Westwater Canyon yielded weaker positive
relationships, compromised by the 1993 data point (early hatch and high water) and no YOY collected
there in 1995 (Figure 4).
A spawning period, calculated for the Above Canyon and Canyon sub-reaches, was plotted
against Colorado River flow and temperature. Spawning period was back calculated for an entire sample
of YOY. The sample chosen for each year's analysis represents the earliest collection of a sizeable
sample of young of year (Figures 4 and 5). The spawning period appeared to be very similar between the
sub-reaches. The greatest discrepancy in onset of spawn between sub-reaches occurred in 1994 when
chubs first spawned on O1 June above the canyon and not unti109 June in the canyon. Similarly the
spawning concluded on the same date in both sub-reaches in 1993 and 1994, but continued as much as 10
days later above the canyon in 1992. Spawning commenced in Westwater Canyon in June, at flows
ranging from 11,200 cfs in 1992 to 20,400 cfs in 1996. The spawning period lasted through the month of
June during the low water years of 1992 and 1994 and through much of July in 1993 and 1996.
Additional back calculations of young of year total lengths collected on 15 August 1996 indicated
spawning commenced in the canyon on 19 June and concluded on O1 August that year -the longest
annual spawning period during the current study. Young of year chubs collected in Westwater Canyon
were all spawned following the annual peak flow. Spawning in Westwater Canyon commenced as soon
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