7729

• UCREFRP Catalog Number: 7729
• Author: Valdez, R. A., W. J. Masslich and A. Wasowicz.
• Title: Annual Summary Report - 1990\
• USFW Year: 1991.
• Copyright Material: NO

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1980-81). These differences are unexplained but may represent variable spawning success between
the two years.

4.3 Summary of Colorado Squawfish Habitat Assessment

Habitat suitability assessment of the Dolores River for Colorado squawfish was divided into three
components: 1) physical attributes; 2) chemical attributes and 3) biological attributes. Each of these
components is address in detail in the following sections.

43.1 Physical Attributes

Habitat suitability of the Dolores River is influenced by the physical attributes of the system such as
flow, temperature, substrate characteristics, habitat structure, and channel morphology. Measuring
these physical attributes individually is generally not difficult. However determining the combination
of these physical attributes most suitable to a species like the Colorado squawfish is not well defined,
particularly since the fish cannot be observed directly. Consequently, for the purposes of this study,
it was necessary to use information collected on physical habitat for Colorado squawfish from other
river systems and assume that if physical attributes of the Dolores River fall within the same range,
physical habitat in the Dolores River is probably suitable and does not represent a limiting factor in
the system.

Criteria for physical habitat suitability of the Dolores River is based on habitat suitability index curves
developed by Valdez et al. (1987), for endangered fish in the Upper Colorado River Basin. Results
of studies of the Colorado squawfish in other Upper Basin drainages are also used to evaluate the
suitability of the Dolores River. Information collected from the Yampa and White rivers was of
particular interest, since these systems may be functionally comparable to the Dolores River in terms
of their role in the life history of the Colorado squawfish.

Flows

The Dolores River drainage exhibits a hydrograph that is generally typical of most Upper Colorado
River Basin drainages. Beginning in mid to late March, flows usually increase dramatically due to
rapidly warming temperatures that cause a sudden melt of mid-elevation snow pack. This early runoff
can peak quickly and begin to subside in mid to late April, when flows may increase again due to melt
of higher elevation snowpack. Following spring runoff, flows gradually subside until mid to late July.
From late July through September, the climate in the Dolores River region is often dominated by
moisture-laden Pacific air masses transported by a southwesterly flow of air. The result of this
"summer monsoon season" is frequent high intensity storms that result in brief flow spikes which can
be relatively large in magnitude.

For purposes of assessing the flows of the Dolores River system, the study area was divided into two
reaches, each with a distinct hydro graph. These reaches include: 1) the Dolores River above the
confluence of the San Miguel River (above RM 64.4) and; 2) the Dolores River below the confluence
of the San Miguel River (below RM 64.4).

Flows in the Dolores River above the confluence of the San Miguel River are dominated by releases
from McPhee Dam. Although, seasonal inputs from tributary drainages can contribute significant
flows during certain times, the operation of McPhee Dam has the greatest influence on the

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