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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Gill and trammel net catch rates by species by trip for the 2 years of study show no definitive
patterns of fish abundance between trips (Tables 13 and 14). These data reflect lower efforts during
1991.

Netting was not conducted in Reach 6 by BIO/WEST. Electrofishing was the primary sampling
method in this reach. Netting was conducted in Reach 6 by CDOW during 1987-1990. CDOW catch
rates reported for Reach 6 (RM 129-185) were highest for roundtail chub (7.1 fish/1oo feet of
net/overnight set), followed by tlannelmouth sucker (3.9), trout species (1.8) bluehead sucker (1.0)
and channel catfish (0.2). These results were comparable to species composition found by
BIO/WEST in Reach 6 (Table 34), indicating that roundtail chub and tlannelmouth sucker were the
most abundant species in Reach 6.

4.2.3 Seining

Red shiner (98.1 fish/100 m2), sand shiner (69.6) and fathead minnow (54.0) dominated catch rates
when data for all 10 habitat types were combined (Table 15). Catch rates for native species, were
9.2 for roundtail chub, 8.2 for flannelmouth sucker, 6.7 for speckled dace and 2:2 for blue head sucker.
Channel catfish and unidentified suckers represented the only other species with relatively high catch
rates of 2.4 and 1.8, respectively. Limited use of a large seine resulted in the capture of three
species, all non-natives (Table 16).

Catch rates for red shiners, sand shiners and fathead minnow correspondingly dominated catch
rates in eight of ten habitat types (Tables 17-26). Two habitat types not dominated by this species
assemblage were rimes and isolated pools. Speckled dace dominated seining catch rates in rimes
(14.1 fish/1oo m2) followed by channel catfish (13.5) and red shiners (9.5) (Table 24). In isolated
pools, red shiners were most abundant (51.7 fish/100 m2) followed by roundtail chub (13.0), and
fathead minnows (12.6) (Table 26).

Seining was the most consistent fish. sampling technique between reaches. Although sampling
effort was not always consistent between trips or reaches, factors affecting seining catch rates were
not as variable as with other sampling techniques. Still, seining catch rates varied substantially
between the 2 years of study (Table 27). Catch rates were much higher in 1990 than 1991 with the
exception of the first trip (pre-runoff). It is hypothesized that low flows during 1990 created
conditions more conducive to seining and may have concentrated fish and increased catch rates.
However, higher catch rates in Trip 1 of 1991 compared to Trip 1 of 1990, indicated high spawning
success of most species with a strong cohort the following spring.

Of the 14 species captured by seining, five were from backwaters, three from rimes, three from
isolated pools, two from embayments and one each from trickle-fed backwaters, eddies and pools
(Table 28). The three native species, flannelmouth sucker, bluehead sucker and roundtail chub, were
in backwaters. The affinity of these species for backwaters was shared by red shiners and fathead
minnows. Speckled dace was the only native species captured most frequently in rimes, although
catch rates were also relatively high in backwaters.

4.2.4 Fish Species Composition - Past and Present

In order to address Objective 1 of this study, a comparison was made between the 1981 study
(Valdezet al.1982) and the 1990-1991 BIO/WESTinvestigation. Comparisons of catch rates for trips
conducted within the same season of the year are presented in Tables 29 and 30. Species composition
by reach was compared between the two studies in Tables 31 and 32. These comparisons are

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