8133

• UCREFRP Catalog Number: 8133
• Author: Collins, K. and D. K. Shiozawa.
• Title: The Effects of Fish Predation on Backwater Invertebrate Communities of the Green River, Utah\
• USFW Year: 1996.
• Copyright Material: NO

access by smaller fish. We constructed each cage of four panels that were 1.2 in high and two
meters wide. The panels were framed with wood and covered with 1.6 mm fiberglass screen.
The four panels were bolted together and the cage was placed in the backwater and secured
with fence posts placed at each corner. The cages extended 20 to 40 cm above the water
surface, varying, over time, with river depth. The position of the treatments within each
backwater was randomized.
The third treatment allowed us to: (1) determine the combined effect of the smaller fish
(i.e. red shiner, young Colorado squawfish, etc.) on the backwater invertebrate community,
and (2) to check for cage effect (whether any statistical significant differences between the
control treatment and the closed treatment were due to the presence or absence of fish, or to
some physical differences created by the cage).
Sampling_
Enclosures were installed August 6-8, 1992. Samples were initially taken weekly;
August 14-15 (week 1), August 21-22 (week 2), August 28-29 (week 3). After week 3 the
sampling interval was lengthened to approximately biweekly because of decreasing water
temperatures; September 11-12 (week 5), September 25-26 (week 7), and October 16-17 (week
10) (Shiozawa and Barnes 1977). During each sampling period 30 benthic cores (19 mm in
diameter) and five vertical plankton tows (20 cm in diameter) were taken from each treatment
within each backwater. While the total number of core samples taken per treatment was high
(180), the total area sampled over the duration of the experiment was approximately 510
square centimeters. This surface area was low enough that sample removal was unlikely to
significantly influence the treatments. Samples were preserved in a 5 % formalin solution.
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