8278

• UCREFRP Catalog Number: 8278
• Author: Cavalli, P. A.
• Title: An Evaluation of the Effects of Tusher Wash Diversion Dam on movement and Survival of Juvenile and Subadult Native Fish.
• USFW Year: 2000.
• USFW - Doc Type: Salt Lake City.
• Copyright Material: NO

entrainment of larval fish is to reduce flows in the raceway during the larval drift periods. A
reduction in the amount of water diverted would probably reduce entrainment of all life stages of
endangered fish, but the cost of such an action (reduced crop production and power generation)
could be substantial. A comparison of the costs associated with fish exclusion structures to the
costs associated with reducing diversion of water during the larval drift periods should be
completed in order to help make decisions about modifications to the raceway that may be
needed to protect endangered fish.
Tusher Wash Diversion Dam, Thayn Power Plant and pump station, and the Green River
Canal appear to have a negative affect on subadult fish. Large numbers of native fish, including
a razorback sucker, were found impinged on the grate in front of the power plant and pump
station. No endangered fish have been found on the grate since the wall in front of the power
plant was removed, but adult Colorado pikeminnow were caught with electrofishing gear in the
Green River Canal during the summer of 2000 (Tim Modde, U.S. Fish and Wildlife Service,
personal communication). Few fish were found in the Green River Canal when it was dry, but
these numbers were probably affected by diversion of water out of the canal through sluice gates
and the removal of fish by scavengers before sampling occurred; tracks from birds, humans, and
other mammals were noted throughout the canal system. Fishing tackle was also found in the
Green River Canal; local fishermen often catch fish in the canal, and some people walk the canal
when it is dry to capture stranded fish (Kim Olson, Utah Division of Wildlife Resources,
personal communication). Glen Baxter (personal communication), along time resident of Green
River, Utah reported having seen a 38 pound catfish that was caught in the canal several years
ago, and another resident claimed to have found Colorado pikeminnow in his ditch at the end of
the imgation season (Frank Vetere, personal communication with Jeff Beck, Utah Division of
Wildlife Resources). These findings and anecdotal reports suggest that modifications are needed
to keep subadult and adult fish from entering the canal system. However, the debris carried by
the Green River will have to be factored into the design of the modifications in order to keep
maintenance costs at a reasonable level.
Tusher Wash Diversion Dam does not appear to be a complete barrier to upstream
movement by subadult fish when flows are at least 4,800 cfs. The average catch rate and average
size of most species were not different upstream of the dam compared to downstream of the dam.
The differences in catch rates or average size that were noted can probably be explained by
factors such as small sample sizes (e.g. only three Colorado pikeminnow were captured upstream
from the dam) or differences in habitat availability (e.g. all of the Gila spp. were captured near
Swasey's Rapid, which is found above the diversion dam; at this point, the valley becomes wider
and the average gradient declines. Consequently, riffles are rare and there are no rapids and
below this point, while both of these habitat types are common above this point). The lack of
significant differences could be explained by either similar production and growth upstream and
downstream from the dam or by movement of all sizes offish across the dam. However,
flannelmouth suckers, bluehead suckers, and channel catfish were documented to move upstream
past the dam. Therefore, it seems likely that fish passage at the dam is possible when flows are
approximately 4,800 cfs. However, the average base flow during recent years has been
approximately 2,500 cfs. It is still unknown whether or not subadult fish can move upstream past
Tusher Wash Diversion Dam during periods when the discharge is closer to average base flow
conditions.
None of the radio-tagged Colorado pikeminnow were found to move upstream past
Tusher Wash Diversion Dam. One fish was found in the same location for several weeks. This
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