7224

• UCREFRP Catalog Number: 7224
• Author: Kaeding, L. R., B. D. Burdick, P. A. Schrader and C. McAda
• Title: Temporal and Spatial Relations between the Spawning of Humpback Chub and Roundtail Chub in the Upper Colorado River
• USFW Year: 1990
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

SPAWNING OF HUMPBACK AND ROUNDTAIL CHUBS
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PC I
FlcuxE 1.-Principal component (PC) scores for 597 fish captured in the Colorado River at Black Rocks,
Colorado, 1983-1985, and classified in the field as either humpback chub, roundtail chub, bonytail, or unclassified
Gila sp. Within the limits of the polygon there were 146 (54%) humpback chub scores that are not individually
plotted for purposes of graphical clarity. The line Y = -0.123 X, fitted by eye, is shown; Y is PC II, and X is PC
I.
Results
Analyses of Morphologic and Meristic Characters
During the 3-year study, we identified 597 ma-
ture Gila spp. in the field. Of these, we considered
270 as humpback chub, 269 as roundtail chub, 1
as a bonytail (Kaeding et al. 1986), and 57 as un-
classified Gila sp. The principal component anal-
ysis of the morphologic measurements revealed
two clusters, humpback and roundtail chubs (Fig-
ure 1). The first two principal components (PC I
and II) explained 85% of the variation in the data
matrix. The line Y = -0.123 X, fitted by eye,
divided the two clusters. Because the slope of this
line is near zero, the in$uence offish size on shape
was almost entirely accounted for in PC I, and the
shearing technique of Humphries et al. (1981) was
not needed (G. R. Smith, University ofMichigan-
Ann Arbor, personal communication). In analyses
of Colorado River Gila spp. that included shorter
specimens, such lines had positive slopes near un-
ity (e.g., Bookstein et al. 1985). The gradual slope
of our line may result from the relatively narrow
length-class of adult fish examined.
The most important morphologic characters for
distinguishing species were depth of the nuchal
depression and caudal peduncle depth (Table 1).
Of the taxonomic assignments made in the field,