1108

• UCREFRP Catalog Number: 1108
• Author: Valdez, R. A.
• Title: Fisheries Biology And Rafting Annual Summary Report - 1987
• USFW Year: 1988.
• USFW - Doc Type: ‎(Contract no. 6-CS-40-03980)‎.
• Copyright Material: NO

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Electrofishing

The highest catch rate with electrofishing gear (Table 6) was for carp (360.7
fishj10 hours) and channel catfish (206.8). The catch rates for red shiners
(220.8) and sand shiners (51.3) probably do not accurately reflect the actual
densi ties of these species relative to the other larger species, because of
differences in capture efficiency by size and our inability to net many of the
small stunned fish with the large mesh of the dip net bags. There are probably
many more shiners than these catch rates indicate.

Catch rates for Colorado squawfish and humpback chub were 2.8 and 2.6 fishj10
hours. The only other fish caught in significant numbers was the flannelmouth
sucker (67.5 fishj10 hours).

Gill and Trammel Nets

Catch rates for gill (Table 7) and trammel nets (Table 8) are presented
separately as the number of fish per 100 hours per 100 linear feet of net.
Unlike 1986, when sampling effort with gill and trammel nets was about equal,
(425.0 hours for gill nets and 357.4 hours for trammel nets), the effort
expended with gill nets was greater in 1987. Various dimensions and mesh sizes
of gill nets were used in 1987 to increase the catch of chubs in Cataract
Canyon and use of the Achilles "sportboat" allowed access to more areas and
decreased travel time between net sets. In 1987, gill nets were set for a
total of 1164.2 hours while trammel nets were set for 357.2 hours. Although
only three species of fish were captured with trammel nets, higher catch rates
were seen with this gear than with gill nets. Catch rates with both types of
gear were highest for carp, because of their relatively greater abundance and
perhaps because the serrated first dorsal and anal spines of this species tend
to wrap readily in nets. No Colorado squawfish were caught with either gill or
trammel nets, but several chubs were captured with gill nets, including four
humpbacks and one suspected bony tail.

Seines

The seine information presented in Table 9 represents catch rates from a total
of eight habitat types (backwater, shoreline, pool, isolated pool, run, eddy,
embayment, and concavity). These catch rates are presented by habitat type in
Tables 10-17. When viewed across all habitats, catch rates with seines were
highest for red shiner (19.74 fish/10 square meters), channel catfish (4.20),
sand shiner (1.99), and fathead minnow (1.97). The next highest catch rate was
for Colorado squawfish (1.77). Young fish, tentatively identified as humpback
chub, were caught at a rate of 0.0038 fish/10 square meters. All chubs
combined accounted for 0.6638 fish/10 square meters.

Based on catch rates, backwaters were preferred by all species except for
channel catfish, which were more abundant in shorelines (7.75) and eddies
(5.93). The relatively high catch rate of larvae, YOY and juvenile Colorado
squawfish in backwaters (1.73) supports the hypothesis held by many researchers
that this habitat is important to this endangered fish, but the high densities
of other fishes, particularly non-native species, strongly suggests competition
and predation. Catch rates of red shiners (24.18), channel catfish (5.36),

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