7046 ‎(2)‎

• UCREFRP Catalog Number: 7046
• Author: Valdez, R. A., W. J. Masslich and A. Wasowicz.
• Title: Final Report\
• USFW Year: 1992.
• Copyright Material: NO

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presented as a means of indicating possible changes that have occurred in the Dolores River in the
last 9-10 years. Based on differences in catch rates and species composition between BIO/WEST's
1990 and 1991 data, the potential for a high variability in catch data is apparent. Differences between
the two studies were expected especially with differences in gear types, efficiency and methods. Since
these differences could not be evaluated, comparisons between catch data from the two studies
focused on gross differences in composition and catch rates.

Catch rates for netting and electrofishing combined (Table 29) showed little differences between
the two studies. No unusual discrepancies or patterns were identified between the two data sets.
Catch rates for seining also showed no major differences between the two studies (Table 30). One
minor difference was the high catch rates for red shiners and roundtail chubs by the Service in April
followed by a decline in July. BIO/WEST's data suggests an opposite pattern, low catch rates in April
followed by higher catch rates in July as individuals from the current year class became prominent
in the catch. Differences may have reflected a poor year class of these two species during the
Service's study in 1981.

No major changes in fish species composition captured in gill nets, trammel nets and by
electrofishing were evident between the two studies (Table 31). Several trends were noteworthy and
suggested subtle changes in species composition. Except for Reach 1, consistently lower catch rates
of round tail chub by BIO/WEST suggest a decrease in abundance of this species. Conversely,
consistently higher catch rates of flannelmouth suckers in all reaches except Reach 1 indicate an
increased abundance of this species, particularly higher in the drainage.

With the exception of compositional shifts between sand shiners, red shiners and fathead
minnows, seining data showed very few changes in species composition of fish captured seining since
1981 (Table 32). The shift in composition between red shiners, sand shiners and fathead minnows
probably represents natural variation in populations of these prolific species.

4.3 Summary of Colorado Squawfish Habitat Assessment

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

4.3.1 Physical Attributes

Habitat suitability of the Dolores River was influenced by physical attributes such as flow,
temperature, substrate characteristics, habitat structure, and channel morphology. Measuring these
physical attributes was generally not difficult, but determining the combination of attnbutes most
suitable to a species like the Colorado squawfish is not well defined, particularly since the fish cannot
be observed directly. For the purposes of this study, it was necessary to use information collected
on physical habitat for Colorado squawfish from other upper basin rivers. We assumed that physical
habitat of the Dolores River was suitable and not limiting if its physical attributes were within the
range in areas of other rivers used by the species.

Criteria for physical habitat suitability were based on HSI curves developed by Valdez et ale
(1987), for endangered fish of the Upper Colorado River Basin. These HSI curves were developed
using data collected on various life stages of Colorado squawfish between 1964 and 1985. Studies of
Colorado squawfish in other upper basin drainages were also used. Information collected from the
Yampa and White rivers was used to describe habitat requirements, since these systems may be