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

i r
males have long anal fins (when compressed the anal fin will
extend beyond the origin of the caudal fin) while females
have shorter anal fins that do not extend beyond the origin
of the caudal fin. These relationships are not absolute but
are valid for a large proportion of the specimens (e.g.,
85-90% in some studies). Mass marking of small fish has been
done in a variety of ways with varying results. These
marking techniques should be reviewed to select some marks
for testing the effects on the fish, retention, and recovery.
The marking of small fish would allow investigators to
determine the extent (speed and distance) of movement and add
to our understanding of the significance of this dispersal
mechanism. For example, several of the confirmed spawning
areas for Colorado squawfish may be contributing the majority
of the young for the system and, therefore, may be highly
critical in keeping the species from becoming extinct.
o Obtain essential information on the
the Colorado squawfish, other rare
that are common in the upper basin.
biology and habitat requirements for
species, and selected endemic species
- Determine the extent and significance of downstream larval movement
(both passive drift of early larvae and active movement of advanced
larvae) of the Colorado squawfjsh as a potential mechanism for
populating suitable nursery areas.
- Examine the availability and size of food organisms (plankton and
benthos) in the shallow backwater habitats of the upper basin to
determine if the quantity (abundance) and quality (size) of potential
food organisms is a limiting factor in survival of young rare fish.
Conduct studies under controlled conditions (e.g., hatchery or
laboratory) to determine food preference of young rare fish.
- Review the systematics of the Gila sp. through coordinated, concurrent
studies on the same specimens.
Rationale - Gaps exist in the knowledge of the biology and
habitat requirements of the Colorado squawfish. For example,
habitat utilization curves for adult squawfish have only been
developed for spawning. In addition, the extent and
significance of downstream larval movement needs further
study since it may be critical to the survival of the
species. Some life history and habitat requirement
information has been collected on the razorback sucker but we
still do not have adequate information to provide sound
biological opinions regarding this rare species. Very little
information is known about the biology and habitat
requirements of the humpback and bonytail chubs. The
bonytail chub is on the verge of extinction, the humpback
chub is found primarily in two major areas of the UCRB, and
the razorback sucker is rare. Mortality of the young rare
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