5001

• UCREFRP Catalog Number: 5001
• Author: Nicola, S. J.
• Title: Fisheries Problems Associated With the Development of the Lower Colorado River.
• USFW Year: 1981.
• USFW - Doc Type: \
• Copyright Material: YES

• • {
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certain that construction of the three main storage dams changed river
conditions sufficiently to either contribute further to the decline or
prevent the natural recovery of these species.
The squawfish is now extinct below Lake Mead almost certainly due to the
fact that it was denied access to upstream spawning areas. The last
verified capture of this species was in 1967 (Hinckley 1973). The humpback
chub was never reported from the lower river other than from just below the
Hoover Dam site. It has not been taken since the dam was constructed and
is also extinct in the lower river.
The bonytail chub may persist in small numbers in Lakes Havasu and Mohave.
Occasional reports are received of bonytail being taken by fishermen. The
last verified capture was of a 2.5 kg specimen caught just below Davis Dam
in 1975. The humpback sucker is faring somewhat better than the chub.
Adult specimens are taken occasionally by biologists as well as fishermen
in parts of the lower river. Both the bonytail and the sucker are apparently
able to reproduce in the Lower river, although they are nowhere.. abundant and only
one juvenile specimen has ever been encountered--a humpback sucker taken in
a canal in Imperial County.
One effect of the changed river environment was that conditions became more
favorable for exotic species. Channel catfish (Ietalurus purcetatus), carp
(Cyprinus carpio), largemouth black bass (Micropterus salmoides) and other
sunfish (Centrarchidae), and rainbow trout (SaZmo gaiz~irceri) had been planted
in the. river at various times earlier in the century, but had. never become
abundant. The Coldwater discharge. of Hoover Dam. created. ideal conditions
for rainbow trout and a hatchery was soon built below the dam to support a
growing trout fishery in this section of the river. The black bass. and sunfish
seemed to benefit most from increased water clarity, while the. carp and
channel catfish appeared to benefit from "stabilized" flows. As the fisheries
for the exotic species expanded it was only natural that biologists should
concentrate their efforts on managing these and others that might be suited
to the changed river environment, rather than the native fishes.
Until the dams were built, use of the lower river for fishing or other forms
of recreation was low. Following completion of the three major dams,
recreational use, primarily fishing, expanded greatly. Although there are
no early estimates of angler use, the good fishing in Lake Havasu in the
1940's (0.5 fish per angler hour; Dill 1944) had attracted enough fishermen
that by 1965 the catch rate had declined to less than 0.2 fish per hour.
These statistics are probably indicative of a trend throughout the lower
basin, for by the early 1960's biologists were attempting to improve fishing
by adding new species to the fauna. In the late 1950's and early 1960's,
striped bass (Mororee saxatiZis) and flathead catfish (PiZodictis oZivaris)
were successfully introduced. Although fishing success is generally low for
these species, they have provided angling for trophy-sized fish, perhaps
filling the role formerly played by the Colorado squawfish.