7739

• UCREFRP Catalog Number: 7739
• Author: Muth, R. T. and T. P. Nesler.
• Title: Associations Among Flow and Temperature Regimes and Spawning Periods and Abundance of Young of Selected Fishes, Lower Yampa River, Colorado, 1980-1984 - Final Report.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: NO

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were assigned to a larval phase or the juvenile or adult developmental periods (Snyder 1976), measured
(total length, TL) to the nearest millimeter, and enumerated. All data for each sample were entered into a
computer database (MANAGE or ~).
Eight of the more commonly coUected fishes were selected for our analyses; four natives (Gila sp.,
speckled dace, bluehead sucker, and Dannelmouth sucker) and four nonnatives (red shiner, sand shiner,
fathead minnow, and redside shiner). Fish were classified as age-O (aU taxa) or older (nonnatives only) by
relating data on date of capture and specimen TL and developmental phase or period with available,
taxon-specific information on typical TL at hatching, early growth rates, length at end of first year, and
spawning period (see Appendix A).
Initiation and duration of the spawning season for each taxon per year were estimated from
length-frequency distn"butions of age-O fish organized by sampling dates and using available information on
TL at hatching and early growth rates (see Appendix A). Two spawning-period parameters for each taxon
were produced from these estimates: (1) total number of days in the spawning season (SPAWN-T) and (2)
number of days, beginning April 1, to initiation of spawning (SPAWN-I). April 1 was selected as the
starting date because, typicaUy, ice covering the river breaks up and river discharge, water temperature, and
extent of low-velocity habitat begin to increase in April; these events were presumed to be biologicaUy
relevant to spawning of Yampa River fIShes.
Indices of relative abundance of age-O or older fish for each taxon by river reach and over aU
reaches (total) per year and by reach over aU years were calculated as number of fISh collected per area
seined (catch-per-unit-effort; CPUE) and percentage of all samples in which a particular taxon occurred
(percentage of occurrence; PO). In calculating these indices for age-O fISh, only samples collected on or
after estimated initiation of spawning for each taxon per year were included in analyses. According to
Ricker (1975) and others, values of CPUE are related in a constant or predictable way to population size,
and changes in absolute abundance over space and time will be reflected in CPUE values. Haynes and
Muth (1982) discussed strengths and weaknesses of CPUE in estimating abundance of fIShes in open,
structurally diverse systems like rivers of the Colorado River Basin.

Correlations.-Correlation coefficients (pearson r) were calculated to better assess interdependency
among years between monthly discharge parameters and degree-days, among annual relative-abundance
indices and spawning-period parameters of fishes, and between annual relative-abundance indices and
spawning-period parameters of fishes and monthly discharge parameters and degree-days. Because of the
survey-sampling nature of the existing fISh database (data were not coUected within an experimental
framework) and because variables were measured or estimated, therefore subject to error, this descriptive
statistical technique was considered most appropriate; our objective was to establish and estimate degree of
association between variables (interdependence), not to describe functional relationships between variables
(i.e., predict one variable in terms of another). The level of statistical significance for coefficients was set at