7761

• UCREFRP Catalog Number: 7761
• Author: Ryden, D. W. and F. Pfeifer.
• Title: San Juan River Recovery Implementation Program Annual Research Report.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

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a shocking boat or ground personnel started at the top of the backwater or
side channel and drove fish to the net by shocking or walking in and agitating
the water. This method enabled the field crew to quickly sample the backwater
and eliminated long-duration net sets. All non-target fish caught in trammel
nets were enumerated by species and returned to the river.

Rare Fish Species

All captured specimens of Colorado squawfish and roundtail chub were
anesthetized using MS-222 (200 mg/Liter of water), weighed, measured, and PIT
tagged. In addition, tissue samples were taken from all Colorado squawfish
and roundtail chub larger than 200 mm TL using standardized non-lethal,
aseptic techniques. Tissue samples were frozen in liquid nitrogen immediately
upon collection and later sent to Genetic Analysis in Smithville, Texas for
analysis. Five adult Colorado squawfish were surgically implanted with
Advanced Telemetry Systems radio tags. After implantation, the radio-tagged
fish were tracked by boat during subsequent sampling trips and by airplane.
Aerial tracking was conducted weekly during the presumed spawning season and
biweekly or monthly during the remainder of the year. Four radio tagged
Colorado squawfish were monitored intensively from the ground during another
study in the summer of 1993.

Compilation of Data

Because of the small number of recorded trammel net sets and limited
catch during July and October, trammel net data were lumped with electro-
fishing data to determine the total number of fish collected each year (total
catch). Electrofishing data were summarized as total catch per unit effort
(CPUE) per raft (i.e. total number of fish collected by all rafts combined in
a reach was divided by the total number of miles or hours shocked by all rafts
in that reach). All samples collected with a corresponding reading for total
time shocked were used in fish per hour calculations. All samples with
beginning and ending river miles were used in fish per mile calculations.
Only fish per mile data are presented in the text; fish per hour data are
given in Appendix I (Tables 9-11). In a few instances neither measure of
effort was recorded and catch per effort could not be calculated. Fish
collected in these samples were included in total catch but not used for CPUE
calculations. CPUE was not examined by time of year as each reach was sampled
only once and comparative data between trips was not available. Although
electrofishing cannot accurately sample small species (e.g., red shiners,
fathead minnows, and speckled dace), these fish were included in the analysis
of fish community composition because of the relatively high number of
specimens they represented. Actual numbers of these smaller species in the
main channel are probably much higher than indicated in the collection data.
Frequency of occurrence for all species was based on the percentage of
collections in which each species occurred. A collection is one
electrofishing sample (usually one mile of electrofishing), one trammel net
set, or one seine haul.

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