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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successful spawning and rearing for these species. High numbers of YOY red shiners, sand shiners
and fathead minnows were also captured, particularly during 1990. High numbers of these species
in 1990 may be a result of favorable spawning and rearing conditions created by consistent low flows
that year.

Native species were prominent in the middle reaches of the study area (Figure 3). Non-native
species may be more common in the lower reaches because of the Colorado River and in the upper
reaches because of McPhee Dam. Influxes of non-native species from the Colorado River probably
shifted species composition in the lower reaches. In the upper reaches, habitat changes associated
with the operation of McPhee Dam may have altered species composition. Stocking and management
of non-native salmonid fishes below McPhee have also affected species composition in the upper
reaches.

Each of the four major native species exhibited a unique distnbution through the study area as
a percentage of total species composition. Flannelmouth suckers were the most ubiquitous native
species in the drainage, although these were most prevalent in the middle reaches (Figure 4)
Bluehead suckers comprised a higher percentage in the lower reaches, but was common throughout
the study area (Figure 5). Roundtail chubs were most prevalent in the upper reaches (Figure 6), and
percentage of speckled dace was also higher in the upper reaches (Figure 7).

Analyses of seine samples also indicate that natives were more prevalent in the middle and upper
of the study area (Figure 8). The relatively high percent composition in Reach 3 during 1991, was
difficult to explain. A series of flood events that occurred in 1991 may have reduced the abundance
of non-native species in this reach. It is possible that increased composition of native species may
be representative of strong year classes of one or more of the native species, however this was not
reflected in catch rates for 1991.

During Trip 4, 1991, a Roy-tagged flannelmouth sucker was recaptured at RM 528. The fish was
originally handled by the Service on May 14, 1981 at RM 39.5 (Valdez et al. 1982), measuring 474
mm total length (TL) and weighing 1120 gms. The fish was recaptured on April 6, 1991, 13 miles
upstream measuring 512 mm TL and weighing 993 gms. During a period of approximately 9 years
and 11 months the fish grew 38 rom and lost 127 gms. This translates to a growth rate of 3.8
mm/year. The weight loss can be attributed to numerous factors (i.e. condition, observer error, etc.).

4.2 Summary of Fish Collections by Gear Type with CPE Statistics

Results of fish sampling efforts for each gear type are presented in the following sections (Table
2).

4.2.1 Electrolishing

Flannelmouth sucker, roundtail chub, bluehead sucker, carp and channel catfish were the most
abundant species in the catch using canoe electrofishing during both years of the study (Table 7).
Differences in catch-per-effort (CPE) between the 2 years were difficult to interpret but were
probably associated with
one or more factors including: 1) actual changes in density; 2) different conditions (i.e. flow, water
quality) between trips and years; 3) differences in timing of sampling between the 2 years of study.

Highest catch rates for canoe electrofishing (Table 7) were for flannelmouth sucker (105.7 fish/10
hours), roundtail chub (52.8), bluehead sucker (30.0) and carp (29.0). Highest catch rates for Jon

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