6012

• UCREFRP Catalog Number: 6012
• Author: Miller, W. H., D. L. Archer, H. M. Tyus and K. C. Harper.
• Title: Colorado River Fishery Project
• USFW Year: 1982.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

• .
Predation - PicAda and Wydoski (1980) believed that failure of
razorbacks to reproduce successfully may be attributed to predation of
eggs and larvae by exotic species such as the largemouth bass, channel
catfish and green sunfish. Medel-Ulmer (1982) actually found large
quantities of razorback eggs in the stomachs of bluegill, channel catfish
and largemouth bass in Senator Wash Reservoir, California.
Health - No reproduction of Mohave razorbacks has been found in
many years and the adult population is beset by various disease problems,
not the least of which is blindness, apparently caused by parasites
(myxosoma). Upper Colorado River fish also were found to be blind.
Learnaea was commonly found on razorback adults. This species' preference
for slow moving water makes it quite susceptible to invasion by parasites.
However, lack of reproduction and subsequent aging of the population are
the cause of the decline of the species rather than disease.
Other Native and Exotic Species
Four non-endangered native fish species, the flannelmouth sucker
Catostomus latipinnis, bluehead sucker C. discobolus, roundtail chub and
speckled dace, Rhinichthys osculus were common throughout much of the
study area. Flannelmouth suckers were most numerous followed by bluehead
suckers. Speckled dace were common to prevalent in nearly all strata.
Roundtail chub were prevalent in the upper Colorado River, particularly
in Colorado upstream of the Utah line, but were much less prevalent in
the Green River.
Relatively uncommon to rare native species in the study area were
the mottled sculpin Cottus bairdi and mountain whitefish Prosopium
Williamsoni. They were seldom encountered because their preferred
habitats that were outside the study area. Many endemic fish were
tagged with Floy anchor tags to identify recaptures at sampling stations.
Relatively few recaptures signified that recaptures did not significantly
influence catch rate values.
Fifteen non-native fishes (exotics) have become established in the
Upper Colorado River Basin. Most significant were the red shiner
Notropis lutrensis, channel catfish Ictalurus punctatus and fathead
minnow, Pimmepheales promelas, which made up a major segment of the fish
population.
Other species that were widely distributed but were found in moderate
numbers include the carp (Cyprinus carpio), sand shiner (Notropis stramineus)
and black bullhead (Ictalurus melas). Largemouth bass (Micropterus
salmoides) were widespread in the upper Colorado River, while smallmouth
bass (M. dolomieui) were common in the Green River throughout the Uintah
Basin. Eight other exotic species were collected occasionally. None
were regarded as significant-nor expected to proliferate. Redside
shiners (Richardsonius balteatus) were collected in Dinosaur National
Monument. In University of Idaho studies, the redside shiner, a native
species of the Columbia River system, was found consistently intermixing