7823

• UCREFRP Catalog Number: 7823
• Author: Miller, W. H., et al.
• Title: Colorado River Fishery Project, Part II, Final Report, Field Investigations.
• USFW Year: 1982.
• USFW - Doc Type: \
• Copyright Material: NO

turbid, high in nutrients. Primary production is low, benthic
invertebrates dependent on substrate. Fish species composition was
variable but dominated by cyprinids, catostomids, and influenced by
introduced fish species.
Following Joseph et al. (1977), the Green River should be included
in the third subdivision. As indicated by Smith (1981), the habitat
for periphyton and benthos is limited by high discharge relative to
channel capacity. Fishes are, therefore, exposed historically to an
"unsteady" supply of food, swift current, and great seasonal fluctuation
in stream discharge.
High stress associated with life in the lower riverine zones
results in a lower productivity than occurs in upstream headwaters
of the Green. This is evidenced by a sharp species segregation which
represents a demarcation between the short growing season, but good
food conditions of headwaters versus the stressful discharge and poor
food conditions of life in the main channel. According to Smith (1981),
these factors may explain the development of longevity and large size
of endemic large river forms (such as the Colorado squawfish) in the
main channels of the Green River.
Because seasonal differences in discharge dominate the Green River
ecosystem, sampling schedules were designed to measure the different
conditions existing in the different river runoff stages. Discharge
records were obtained from the U.S. Geological Survey'(USGS) and utilized
• to construct discharge hydrographs for 1979-1981 (Figures 6 to 8). Pre-,
post-, and runoff periods for each year were delineated from inspection
of these hydrographs as follows:
Prerunoff Runoff Postrunoff
1979 1 /1 - 4/19 4/20 - 6/30
(not sampled) (not sampled) 7/1 - 12/31
1980 1 /1 - 4/19 4/20 - 6/30 7 /1 - 12 /31
1981 1/1 - 4/29 4/30 -,6/14 6/15 - 12/31
(not sampled)
Runoff in 1979 and 1980 was similar both in duration and magnitude.
In 1981, however, runoff was less sharply defined and of much smaller
magnitude.
Physicochemical description of strata
As stated previously, various physicochemical parameters were
measured in order to characterize strata. Mean water temperatures
generally reflected the order in which strata were sampled (i.e.,
B-A-F-E-D-C). Mean water temperatures for each stratum during runoff
were higher than during prerunoff but were much less variable, reflecting
both higher. stream discharge and less variability in air temperatures.
Lower discharges and increased summer air temperatures in the post-
runoff period resulted in more variable water temperatures. Mean
• water temperatures for all strata except C and D increased regularly
from prerunoff through postrunoff. Strata C. and D include Gray Canyon
and Desolation Canyon, respectively, and are deeper (Table 6, Figure 9)
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