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Last modified
7/14/2009 5:02:31 PM
Creation date
5/22/2009 5:00:09 PM
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UCREFRP
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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<br />Diet overlap values were considered biologically important only for comparisons with certain <br /> <br /> <br />size-interval, river-reach groups of five fishes. <br /> <br /> <br />Because interspecific demand for resources might not exceed supply, Bowen (1983) <br /> <br />noted that even extensive diet overlap is not conclusive evidence for competition. <br /> <br />Accordingly, McAda and Tyus (1984), who also used Schoener's index to examine diet <br /> <br />overlap between YOY Colorado squawfish and nonnative fishes in the Green River, <br /> <br /> <br />suggested that the high diet overlaps they observed between Colorado squawfish 22-40 <br /> <br />mm TL and channel catfish 19-55 mm TL (overlap value = 0.60) and especially red shiner <br /> <br /> <br />15-69 mm TL (overlap values 0.70-0.80) might reflect shared use of abundant resources, <br /> <br /> <br />primarily immature dipterans, rather than competition. The same may be true for the higher <br /> <br />diet overlaps we observed. Ward et al. (1986) reported that chironomids, the principal food <br /> <br /> <br />category resulting in high diet overlap, were among the more common benthic invertebrates <br /> <br />in the Colorado River System. <br /> <br /> <br />We observed that overlap values were generally higher and, for most fishes, diet <br /> <br /> <br />diversity was greater in the lower than upper reach, perhaps because food resources were <br /> <br />more abundant and diverse in backwaters of the lower reach. Based on observations <br /> <br />during summer and fall 1979-1988, Haines and Tyus (1990) found that backwaters in the <br /> <br /> <br />upper and lower reaches were similar in mean surface area, but that those in the lower <br /> <br />reach were shallower and warmer, conditions that may favor higher productivity. Also, <br /> <br /> <br />within the upper reach, Grabowski and Hiebert (1989) noted that during summer and fall <br /> <br />1987-1988 concentrations of backwater nutrients, particulate organic matter, phytoplankton, <br /> <br /> <br />zooplankton, and benthic macroinvertebrates (particularly chironomid larvae) increased <br /> <br />progressively downstream. They suggested that this trend was due to attenuation of flow <br /> <br />releases from Flaming Gorge Reservoir at downstream sites which reduced the degree of <br /> <br />13 <br />
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