9544

• UCREFRP Catalog Number: 9544
• Author: Collins, K., P. and D. K. Shiozawa.
• Title: The Effects of Fish Predation on Backwater Invertebrate Communities of the Green River, Utah.
• USFW Year: 1994.
• USFW - Doc Type: Provo, UT.
• Copyright Material: NO

rom a ), and Colorado squawfish. Together these three species comprise 93 - 95%
of all backwater fishes (Haines and Tyus 1990). All three species consume
chironomid larvae, and the red shiner and young Colorado squawfish also consume
zooplankton, and semi-aquatic insects (Catherine A. Karp, personal communication).
METHODS
Study area
The Green River originates in Wyoming and is part of the Colorado River
drainage,joining the Colorado River in southeastern Utah. 404 km above its confluence
with the Colorado River it enters Ouray National Wildlife Refuge (ONWR). When it
reaches ONWR it has a drainage area of 47,723 km2 with an average high flow of
11,926 cfs and an average low of 3,530 cfs (U.S.G.S. data). All backwaters used in
this study were located on ONWR and were shallow (approximately 0.75 m to 1.0 m
deep) with no measurable current except when the wind blew. Secchi disk visibility
averaged 22 cm, and the substrate was composed of soft sediments under a thin
(approximately 4 cm) layer of flocculent material.
Experimental design
A randomized block design was used with three treatments per backwater. The
treatments were: (a) a four m2 (2 x 2 m) control area, marked by posts, which was
open for foraging to all backwater fishes, (b) a four m2 caged area that excluded all
fish, and (c) a four m2 cage with 2.5 cm wide by ten cm high (spaced approximately
ten cm apart) perforations cut into all four sides. These perforations excluded large
fish such as carp (Cyprinus carpio) and channel catfish (Italurus u a us) but
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