7055

• UCREFRP Catalog Number: 7055
• Author: Archer, D. L., L. R. Kaeding and B. D. Burdick.
• Title: A Study of the Endangered Fishes of the Upper Colorado River.
• USFW Year: 1985.
• USFW - Doc Type: Grand Junction, Colorado.
• Copyright Material: NO

Hatching dates for individual larvae were estimated by back-calculation
using an equation developed by Haynes et ale (1985):

AGE = - 76.71 + 17.50 TL - 1.06 TL2 + 0.0221 TL3

~here TL is total length (mm) at the time of collection, and AGE is the number
of days since hatching. This equation ~as derived from the gro~th rate of
Colorado squawfish in a hatchery (Hamman 1981b). The median incubation period
for eggs held in 20 C water ~as 102 hr (Marsh 1985); therefore, 4 days were
subtracted from hatching date to determine spawning (egg deposition) date.
The peak spawning period ~as considered to be when the median 501 of the
Colorado squa~fish larvae were estimated to have been spawned. Estimated
spa~ning dates from the upper reach (Reach 4) were compared ~ith ~ater-
temperature and discharge data from the USGS gage at the Colorado-Utah border.
Similar comparisons were not made for Reaches 1-3 because gage data are not
available for these areas.

Fall Dost-larval_ aqe-O samolinq (Obiective 2)

The annual reproductive success of Colorado squa~fish ~as estimated by
systematic sampling of the small fishes in reaches 2-4--the riverine part of
the study area. Investigators began at the upstream end of the reach and
sampled the first backwater or embayment encountered in each 5-mi interval as
they moved do~nstream. Sampling at each site consisted of t~, non-
overlapping seine hauls in the back~ater and two similar seine hauls in nearby
shoreline habitats. Each haul ~as treated as a separate sample. The size of
each area seined ~as quantified and the mean depth and velocity of the ~ater,
as well as the dominant substrate size, were measured at two equidistant
points along a transect through the center of the area seined. water
temperature was recorded. Area seined ~as dependant on back~ter size and thus
varied among sample sites, but generally did not exceed 250 m. Samples were
taken ~ith 1/4-in-mesh (6-mm-mesh) seines in 1982 and 1/8-in (3-mm) seines in
1983 and 1984. All fish were identified in the field, enumerated, and released
alive in 1982. In 1983 and 1984, fish smaller than about 40 mm long ~ere
preserved in 101 formalin and later identified in the laboratory under a
binocular microscope. These changes in gear and identification procedure
between 1982 and subsequent years resulted from our belief that small Colorado
squawfish were escaping the 6-mm-mesh seine and that many of those captured were
too small to be accurately identified in the field. River~ide surveys ~ere
conducted once in 1982 (September). However, because we were also interested in
the temporal effect of sampling on the relative abundance of these young
squawfish, two surveys were conducted in 1983 (September and October) and three
in 1984 (August, September and October). Data are summari2ed as the number of
Colorado squawfish captured in back~ater habitats per 10 m swept ~ith the
seine. Data are pooled ~ithin ID-mi-long reaches for graphical presentation and
~ithin the four study reaches for statistical analysis.

Statistical analysis

Total displacement (distance between the most upstream and the most
downstream locations) of radio-equipped Colorado squa~fish ~as compared among
years and river reaches, as well as among fish size groups. Preliminary
analyses ~ere conducted to determine ~hether fish size ~as related to distance
moved. Three separate comparisons ~ere made, ~ith fish grouped into one of t~o

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