7771

• UCREFRP Catalog Number: 7771
• Author: Muth, R. T. and D. E. Snyder.
• Title: Diets of Young Colorado Squawfish and Other Small Fish in Backwaters of the Green River, Colorado and Utah.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

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ex; = 1 - 0.5 CE IpXi - rTIl )
1=1

where D. is the number of food categories, Pxi is the proportion of food category 1

(expressed as mean of volume percentages) in the diet of species ~ (Colorado squawfish),

and Pvi is the proportion of food category 1 in the diet of species y. (other fishes). Values

range from 0.0 (no overlap) to 1.0 (complete overlap). When data on resource availability

are absent, Schoener's index is one of the best indices available for calculating resource

overlap (Hurlbert 1978, Linton et al. 1981, Wallace 1981). Diet overlap is useful in helping

to elucidate food relationships among species and has been considered biologically

important when values exceed 0.60 (Zaret and Rand 1971, Mathur 1977, Matthews and Hill

1980, Galat and Vucinich 1983, Michaletz et al. 1987).

RESULTS

Digestive tracts from 2554 fish representing 15 species were examined for food

items; less than 3% were empty, mostly from fish ~ 13 mm TL. After subsets with less

than six specimens containing food were eliminated from the dataset, 2297

specimens representing nine species remained for diet analyses. Native fish

included 972 Colorado squawfish (7.5-73.0 mm TL, mean 19.1),35 speckled dace

Rhinichthvs osculus (23.1-39.8 mm TL, mean 28.1), 42 blue head sucker Catostomus

discobolus (23.0-58.9 mm TL, mean 35.9), and 21 flannelmouth sucker C. latipinnis

(32.0-64.3 mm TL, mean 47.9). Nonnative fish included 729 red shiner (11.3-74.5 mm TL,

mean 29.1), 92 sand shiner Notropis stramineus (22.2-53.2 mm TL, mean 31.0), 330

fathead minnow Pimephales promelas (11.0-65.9 mm TL, mean 32.5), 58 channel catfish

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