7422

• UCREFRP Catalog Number: 7422
• Author: Valdez, R. A. and W. J. Masslich.
• Title: Winter Habitat Study of Endangered Fish - Green River.
• USFW Year: 1988.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

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3.4 HSI aJRVE DEVELOPMENT

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winter habitat suitability index (HSI) curves were developed for depth,
velocity, and substrate based on the radiotagged adult Colorado squawfish and
razorback suckers monitored during this study. Separate curve sets were
developed for each species.

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CUrve development followed a set procedure. Only measurements taken during the
2-hour monitoring period were used, since they represented a consistent set of
measurements. These included the 2-hour observations taken in conjunction with
the 24-hour monitoring. A single observation was defined as a set of
measurements taken on a fish remaining stationary for 15 minutes. Thus, the
measurements associated with a fish that remained stationary for 1 hour were
weighted as four measurements; and measurements on a fish that was stationary
for 2 hours were weighted by eight. Habitat measurements were not used to
generate HSI curves if the fish was not stationary for 15 minutes.

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Raw data values for depth and velocity were grouped into O.l-foot classes and
the frequency in each class was plotted to reveal the distribution of the data.
Velocity measurements were all converted to positive values. This was done for
the following reasons:

1. IFIM models do not consider negative velocity and will
assign negative velocities a utilization value of zero.

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2.

Information does not exist to suggest that these fish would
differentially utilize velocity regimes based upon whether
the current is flowing upstream (as in an eddy effect) or
downstream.

3.

Consideration of both negative and positive velocities
considers actual microhabitat conditions.

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A smoothed curve was generated to fit the raw data histogram for depth and
velocity. The generalized Poisson model (Bovee 1986) best described the
distributions of raw data. These depth and velocity curves were placed on a
scale where maximum utilization was assigned a value of 1.0.

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The dominant and secondary substrate associated with each point measurement
were both used to generate the HSI curve. These were placed in classes that
combined each of the six substrate types into a total of 36 possible
combinations. A maximum utilization of 1. 0 was assigned to the substrate
classification with the highest frequency.

The distribution of habitats (backwaters, runs, pools, etc.) used by
radiotagged fish was also presented in histograms to show the specific habitats
where measurements of depth, velocity, and substrate were taken.

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