8105

• UCREFRP Catalog Number: 8105
• Author: Haines, G. B., D. W. Beyers and T. Modde.
• Title: Estimation of Winter Survival, Movement and Dispersal of Young Colorado Squawfish in the Green River, Utah.
• USFW Year: 1998.
• USFW - Doc Type: Recovery Program Project 36,
• Copyright Material: YES

274

Y.K. CONVERSE ET AL.

Table V. Width to depth ratios (W:D) measured at arbitrary cross sections (Schmidt
and Graf, 1990) summarized by reach

Reach

RM

W:D

Average W:D

Reach I

62
63.4
64.1
65

67.1
67.8
68.2
70.2
70.7
71.2
71.8
73.5

73.8
74.2
74.6
76.1

20.7
16.8
21.7
19.2

13.6
66.5
31.6
20.6
24.1
29.6
49.7
36.9

13.2
20.1
19.2
15.4

19.6

Reach 2

34.0

Reach 3

17.0

considered fixed in this analysis. Densities of subadult humpback chub were logwtransformed to correct
for heteroscedasticity (Zar, 1984).
To compare the total abundance of subadult humpback chub among reaches, the mean fish densities
along specific shoreline types were multiplied by the length of each shoreline in a reach.
Effects of flow regime changes on habitat conditions. To assess how changes in flow regime may have
affected habitat conditions (objective 3), we first examined changes in habitat condition associated with
discharge and then examined how the temporal flow regime has been altered by flow regulation. A
multivariate simple linear regression (MSLR) was used to determine if habitat conditions (mean depth,
velocity and cover) changed over the range of interim flow discharges. Separate tests for effects of
discharge, shoreline type and the interaction between discharge and shoreline type on habitat condition
were conducted. Colorado River flow duration curves for pre- and post-dam periods were compared to
examine flow regime changes and to assess the overall effect of flow regulation on habitat conditions.

RESULTS

Physical differences among geomorphic reaches and shoreline types

Reaches 1 and 3 were geomorphically similar and differed from reach 2 in that the width-to-depth ratio
was nearly two times greater in reach 2 (Table V). Percent total riffle area was three to five times greater
in reach 2 (21%) than in reach 3 (6%) or reach I (4%), respectively. These results led us to suspect that
either the distribution of or the physical condition of shoreline types may be influenced by reach. In fact,
although habitat conditions appeared to vary significantly both among shoreline types and between
reaches, a significant interaction between reach and shoreline type suggested differences among shoreline
types were not consistent between reaches (Table VI, Figure 3).
Univariate tests showed that this interaction was largely influenced by substantial differences in depth
and cover between bedrock shorelines in reaches 1 and 2. For example, in reach I, mean depth of bedrock
shorelines (2.39 m) was clearly different from that of all other shoreline types (0.30-1.0 m), whereas in
reach 2, depths of all shoreline types were more uniform (0.25-0.60 m) (Figure 3). Also, in reach 2,
bedrock shorelines had a high frequency of cover, whereas cover was high in debris fan, talus and
vegetated shorelines in both reaches ] and 2, and cover was low in cobble and sand shorelines in both
reaches 1 and 2 (Figure 3).

.~

<&J 1998 John Wiley & Sons, Ltd.

Ref(ul. Rivers: Res. Mf(mt. 14: 267-284 (1998)