9432 ‎(2)‎

• UCREFRP Catalog Number: 9432
• Author: Modde, T. and M. Fuller.
• Title: Feasibility of Channel Catfish Reduction in the Lower Yampa River.
• USFW Year: 2002.
• USFW - Doc Type: Vernal.
• Copyright Material: NO

The high- and low-use periods were determined examining the total catches
of these three native fishes from Table 2. High-use periods coincided mostly
from 1 April to 2 July. However, in 1997 the period extended to 31 July; in
2000, this period ended in late-May. Low-use periods were mostly from 31 July
to mid- to late-October. The dates and number of days within the high- and low-
use periods varied among years. The ratio was lowest in 1996 (2.51). However,
only 38 days between 24 June and 31 July were used for the high-use period
because the passageway did not become operational until 24 June. Therefore,
because 1996 was an abbreviated season, it is probably not a good year for
comparison. The ratio steadily increased to 3.59 in 1997, 4.45 in 1998, 5.69 in
1999, and 7.31 in 2000. In 1999, the second highest ratio was experienced,
indicating that fewer native fish were captured between 31 July and 9 October,
the period when discharges in the Gunnison River were unseasonably higher than
the other four years when the passageway was operated. However, in 2000, the
total volume and mean daily discharge were 48% lower than 1999, the year the
ratio was the highest of all five years (7.31; Appendix; Table I.1.).
This method provides a very cursory examination and its major drawback is
that it does not examine catch directly as a function of discharge, (i. e., it
does not utilize mean daily, weekly, or biweekly discharges to determine if there
is a relationship between concomitant daily, weekly, or biweekly catches of the
three native fishes used). Also, the difference and variability in the dates of
high- and low-use periods, the unequal number of days used among years to
calculate a ratio, and only 1-year (1999) where unseasonably high post-runoff
flows were experienced make it difficult to determine if this method is useful
in ascertaining if these unseasonably high flows negatively impacted native fish
migration through the passageway.
Fish-Use vs. Base-Flow Periods. The total aggregate number of flannelmouth
sucker, bluehead sucker, and roundtail chub and the number of Colorado pi keminnow
collected in the Redlands passageway fish trap between 31 July and 9 October were
plotted against flow volume for the same period for each of the five years. No
relationship was apparent between various Gunnison River flow volumes (low vs.
moderate vs. high) during this period and the number of these fishes (r=0.0158
for flannelmouth sucker, bluehead sucker, and roundtail chub; r=0.00953 for
Colorado pikeminnow) collected in the fish trap (Figure 8). Further analyses
were conducted between the total daily aggregate number of these same three non-
listed, native species and the mean daily discharge for the range of flows
available during 31 July to 9 October for each of the five years. Correlation
coefficients for each of the five years were similar: 1996 (r=-0.17; low-water
period); 1997 (r=-0.26; moderate-water period); 1998 (r=-0.29; low-water period);
1999 (r=-0.22; high-water period); 2000 (r=-0.34: low-water period; Appendix;
Figure I.1.). There was no clear relationship when the total aggregate number
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