7354

• UCREFRP Catalog Number: 7354
• Author: Wydoski, R. S.
• Title: Biological Review of Endangered or Imperiled Fish in the Upper Colorado River Basin.
• USFW Year: 1985.
• USFW - Doc Type: Washington, D. C.
• Copyright Material: NO

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Rationale - The early life stages (larvae, young-of-the-year,
and juvenile) of the rare fish inhabit the warmer shallow
backwater areas or the shallow shoreline of the rivers. This
type of habitat is found primarily in the floodplains of the
rivers where the land is used for agriculture rather than in
the deep canyon areas. Since this region is arid and
irrigation is needed to grow crops, large pumps are used
along various reaches of the rivers of the upper basin.
Irrigation water is needed at the same time that the early
life stages are drifting downstream and occupying the
shoreline areas. There is a possibility that losses from
irrigation pumps could be significant.
Considerations - This possible cause of mortality among the
early life stages of rare fish should be investigated.
First, the number of pumps in various floodplain reaches of
river should be determined. The location of the intakes
should also be determined as well as the capacity of the
pumps to establish the extent of irrigation pumping. The
losses of the early life stages could be estimated by
sampling near the intakes or as the water is pumped into
ditches. However, the impellor of the pump may destroy the
small fish so that identification of species may not be
possible. If the estimated losses of young rare fish is
significant, then the pump intakes can be modified to prevent
or minimize the losses. Installation of such modified
intakes may have to be paid by a natural resource agency
since the private landowners have water rights and may not be
responsible legally to make such changes.
o Take action to control competition and predation on the rare endemic fish
from introduced fish species.
- Prevent further introductions of nonnative fish into the upper basin
through stocking practices and through regulations.
- Reduce suitable habitat for nonnative fish.
Rationale - Competition and predation may play a significant
role in -mortality of the rare Colorado River fish. A number
of the introduced species are not adapted for the large
riverine environment. However, such species (e.g. largemouth
bass and green sunfish) are adapted well for the backwater
areas used by the young life stages of the rare fish.
Actions should be maintained by the state conservation
agencies to prevent further introductions and reduce the
habitat where possible to control the numbers of introduced
fish.
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