7618

• UCREFRP Catalog Number: 7618
• Author: Rose, K. L. and D. R. Hann.
• Title: Summary of Historic Habitat Modeling on the Yampa River Using the Physical Habitat Simulation System
• USFW Year: 1989.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

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relationships that are biologically meaningful. Predictive outputs are not
supported by field observations.

In the Yampa River, where fish are successfully spawning every year and where
adults reside year-round, it can be assumed that the existing natural
conditions are conducive to success of endangered fishes. Model outputs for
the species and life stages examined herein do not predict flow/habitat optima
that even remotely approximate natural flow conditions, and do not fit within
the framework of a normal hydrograph.

The SI curve is the presumed biological link between fish and the available
and usable stream habitat. It is the state-of-the-art of human attempts to
simplify and quantify nature. Of the three variables sampled, water velocity
is probably the most influential factor for spawning and adult habitat
selection. The model output is also the most sensitive to changes in the
shape of the velocity curve. Depth is also important, however, after
exceeding some minimum, depth may not greatly influence habitat selection by
target species. loosely-compacted gravel is probably important for spawning,
although the other uses of gravel as substrate for invertebrates. and/or as
cover, need to be more clearly defined and understood. Cover requirements of
adult Colorado squawfish and humpback chub may dominate their selection of
microhabitat. Biological needs may quickly shift from protected low-velocity
habitats for resting areas, to higher velocity, deeper water which may afford
optimal feeding positions. The preservation of a balance of these habitats
does not appear practicable with present technology without substantive inputs
of empirical biological information.

Stream flow modeling using PHABSIM is more of an art form than a pure science.
Predictive model output (simulations) can be no better than the hydraulic
data. species criteria, and the ability of the model user to calibrate. select
the appropriate software application. and interpret results. However, the
need to quantify habitat for fish and wildlife use is increasingly important
as greater demands are put on an already limited water supply. PHABSIM can be
used as a management tool to assess some physical changes in habitat as a
result of altered streamflow. However, the link between the physical model
and the biological needs of endangered fish species needs significant
improvement before it can be used as a basis for determining instream flow
requirements for the Yampa River. Further, we believe that future field data
collections should focus on critical areas and/or limitin9 habitats rather
than on "representative reaches II so that collection of more detailed. high-
quality, site specific data is feasible.

Finally. we believe that a holistic approach to endangered fish management is
essential. and the species (or life stages) selected for study should reflect
the environmental constraints on the population as a whole. Formulating
stream flow recommendations for adults is meaningless if channel stability,
spawning, larval transport exotic competition and/or other factors are
limiting to the population of target fishes. An estimate of WUA as a function
of discharge is not an end in itself. Unless this index can be related to the
success of endangered fishes in some quantifiable way. it should not be used
as the basis for a State water right filing for protection of endangered
fishes.

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