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

perforated treatment, chlorophyll a levels did not detect trophic cascade effects at the
phytoplankton level as is so often in the case in lentic systems (Carpenter et at. 1987, Johannes
et at. 1989, McQueen 1990, Shapiro and Wright 1984, but see McQueen et at. 1989). It is
somewhat surprising that there was no detectable effect of invertebrate predators on
oligochaetes since both predatory and omnivorous chironomids (such as TanXpus and
Chironomus), as well as corixids of the genus Tricorixa, are known predators of Oligochaetes.
Loden (1974) noted that oligochaetes often break into two pieces when in the grasp of a
predator. Given the regenerative abilities of oligochaetes, this would suggest that oligochaete
biomass may decrease in the presence of predators while their overall density remains about
constant (Wisniewski 1978).
iversi
As shown in Table 5, chironomids appear to be more diverse in control and perforated
areas. These results, coupled with the fact that all of the uncommon genera found were taken
from the control and perforated treatments, suggest that fish predation helps maintain the
diversity of chironomids in backwaters. This is consistent with other studies that have shown
that predation lessens the impact of competition and even prevents the local extinction of some
benthic invertebrates (Connell 1961, Paine 1966, Menge and Sutherland 1976).
Implications
The Colorado squawfish, North America's largest minnow (cyprinidae), now occupies
less than 25% of its historical range and is listed as endangered by the U.S. Fish and Wildlife
Service (Karp and Tyus 1990). While several factors have been implicated in the decline of
the Colorado squawfish, the rarity of juveniles (70-400 mm total length) suggests that the
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