7908

• UCREFRP Catalog Number: 7908
• Author: Valdez, R. A. and R. J. Ryel.
• Title: Life History and Ecology of the Humpback Chub ‎(
• USFW Year: 1995.
• Copyright Material: NO

1-6 . Chapter 1

tracking important physical, chemical, and
biological variables and measures of biological
responses.

Changes in operational regimes during this study
limited opportunities for inducing and observing
long-term biological responses. Rigorous testing of
hypotheses was not possible, because the system
under investigation was not experimentally
manipulated for ichthyofaunal responses, and
replicate systems were not identified and
simultaneously studied. Cause-effect relationships
were first identified through systematic sampling,
and hypotheses were developed from inferences of
these relationships. These hypotheses provided
valuable insight into ecological limitations of
humpback chub and helped to identify mechanisms
and causes of effects from dam operations.

Inferences that identified possible effects of dam
operations on humpback chub were based on
literature and available data collected from this and
other investigations. Few inferences were made for
operational effects on other trophic levels, because
data collected in parallel studies by other researchers
were preliminary and largely unavailable.
Integration with tributary studies, particularly in the
LCR, was also minimal, since information from
these investigations was not available.

Selected physical, chemical, and biological
components were described and quantified, where
possible, to provide an integrated understanding of
those elements of the ecosystem that most likely
affect and limit humpback chub in Grand Canyon.
Data were systematically collected in this study, or
in cooperation with other studies, to minimize
overlap with other research efforts and provide a
comprehensive database to GCES for development
of an integrated report.

STUDY AREA

The Colorado River through Grand Canyon flows
for about 470 kIn (293 mi) from Glen Canyon Dam
to the Lake Mead Inflow at Grand Wash Cliffs
(Fig.I-4, Table 1-2). The river in this area is
controlled entirely by Glen Canyon Dam, except for
periodic floods from tributaries that otherwise
insignificantly affect flow volume. The study area
began at Lees Ferry (RM 0.0), 25.4 kIn (15.8 mi)
do\\nstream of the dam and extended 364 kIn (226

Final Report

mi) to Diamond Creek (RM 226.0). For the
purposes of this report, the area between Glen
Canyon Dam and Grand Wash Cliffs (RM 277.0) is
referred to as the Grand Canyon. This area includes
the lower 25.8 kIn of Glen Canyon (dam to Paria
River), 97.2 kIn of Marble Canyon (Paria River to
LCR), and 347.0 kIn of Grand Canyon (LCR to
Grand Wash Cliffs).

This study area was divided into four study regions
to partition sampling effort by major longitudinal
areas. The four regions were further divided into II
geomorphic reaches (Schmidt and Graf 1990) as
sampling units (See Chapter 2 - STUDY DESIGN).
The four study regions included: (I) Region O--Lees
Ferry to Kwagunt Rapid, (2) Region I--Kwagunt
Rapid to Hance Rapid, (3) Region ll--Hance Rapid
to below Havasu Creek, and (4) Region ill --below
Havasu Creek to Diamond Creek. Regions I, n, and
III were sampled from October 1990 through
November 1993. Region 0 was added to extend the
investigation upstream in January 1993. A fifth
region--Region IV (Diamond Creek, RM 226.0, to
Pearce Ferry, RM 280.0)--was investigated as part
of an aquatic resources study for the Hualapai
Indian Tribe and GCES (Valdez 1993, 1994, 1995).

Reference landmarks along the river corridor were
located to the nearest tenth (0.1) of a river mile (i.e.,
distance downstream from Lees Ferry along the
center of the river) according to Belknap and Evans
(1989), and sample sites were entered in the
database to the nearest twentieth (0.05) of a river
mile. It should be noted that Lees Ferry is 15.8 river
miles downstream of Glen Canyon Dam, and river
miles cited in this report are in reference to Lees
Ferry and not Glen Canyon Dam, unless otherwise
specified. A list of sites commonly referenced in
this report is provided in Table 1-2 with river miles,
river kilometers, and miles and kilometers
downstream from Glen Canyon Dam. The
following is a description of the four study regions
(O-II1). This description and Fig. 1-5 are provided
to farn.iliarize the reader with the physical character
and lithology of the study area, and to develop a
foundation for later discussion of fish habitat
availability and use. (See Chapter 7 - HABITAT).
Detailed descriptions of Grand Canyon geology
were presented by Hamblin and Rigby (1968, 1969)
and Howard and Dolan (1981).