7332

• UCREFRP Catalog Number: 7332
• Author: Valdez, R. A., et al.
• Title: Final Report Habitat Suitability Index Curves for Endangered Fishes of the Upper Colorado River Basin.
• USFW Year: 1987.
• USFW - Doc Type: \
• Copyright Material: NO

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summary of the category 1 and 2 curves identified at Workshop #1 is presented
in Table 5.

Generally, the same line of reasoning was used at each cd terion or
decision point for all three species. The following presents a summary of the
manner in which the experts dealt with each of the nine criteria:

1. Life stage. Data for all three species were partitioned by life stage
because the experts felt that the fish exhibit different habitat use by size or
age. It was pointed out that this use does not necessarily change with
physiological life stage (larval, YOY, juvenile, adult), but may best be
described by size categories. Thus, the life stages proposed by FWS were
retained for the razorback sucker, but were modified for the humpback chub and
Colorado squawfish (Table 4).

The experts agreed that riverine conditions need to be identified to allow
for spawning migration and passage/access by Colorado squawfish and razorback
sucker. However, they felt that using depth, velocity, and substrate
measurements from the current database could not adequately describe these
needs. Although an adult migrating to a spawning area may swim over a great
variety of habitats, its success may be determined entirely by sufficient water
depth and adequate velocity. Temperature was identified as an important key to
the onset and act of migration, but it was noted that the database does not
contain adequate data to develop a temperature curve.

Passage/access was distinguished from migration in that the former is more
site specific and involves all life stages moving both up- and downstream. The
experts felt that site-specific criteria need to be developed for passage
through artifical structures, such as dams and water diversions, as well as
dewatered regions of river. It was also pointed out that access to highwater
backwaters and other riverside habitats is essential, but also site specific.
The experts felt that fish passage is an important consideration which should
be identified as a data gap.

2. River. The experts agreed that for all life stages of each species the
data should be partitioned by river, i.e., Colorado, Green, Yampa, etc., except
where there were no perceived differences in habitat use among these rivers, or
where there appeared to be insufficient data to treat each separately. In many
cases, the experts felt that there may not be differences in habitat use among
rivers, but they wanted to partition the data and run statistical tests. If no
significant differences were revealed, data from different rivers were pooled
by the experts in Workshop #2. Also, data from tributaries were pooled with
data from main rivers where the data came from the tributary mouths; i.e., data
on nonspawning adult razorback suckers from Ashley Creek, pariette Wash, and
the Duchesne River were pooled with data from the Green River because these
tributary mouths were considered habitats of the Green River. For size 5
Colorado squawfish, data from Ashley Creek, pariette Wash, and Brush Creek were
pooled with the Green River, but data from the Duchesne were separated because
the observations were above the mouth of this tributary.

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