7019

• UCREFRP Catalog Number: 7019
• Author: Hawkins, J. A.
• Title: Age and Growth Of Colorado Squawfish From the Upper Colorado River Basin, 1978-1990.
• USFW Year: 1991.
• USFW - Doc Type: Fort Collins, CO.
• Copyright Material: NO

2

Musker (1981) aged 152 Colorado squawfish collected from the Colorado (14), Green
(103), Yampa (26), and White (nine) rivers between 1979 and 1981. Using the scale method, he
back-calculated lengths. He determined a body-length to scale-radius relationship for each river
and used the result in the back-calculation formula. Due to small sample sizes and the lack of
smaller fish, these relationships were not accurate and influenced his results. Musker (1981)
reported lengths of age 1+ fish at 195 mm for the Yampa River and 399 mm for the White River.
However, the first annulus was unknowingly missed and fish 'Were underaged by one year.
Fin-ray sections were used to corroborate scale ages from two fish.

The age information provided by these studies has been valuable and is often cited by
other researchers. With our increasing understanding of the life history of Colorado squawfish,
certain aspects of their age and growth become apparent. There was a need to synthesize the
information we have to date with current age and growth data and relate the known life-history
events of the species with age and growth. Information presented in this report will be expanded
in my master's thesis that will be completed by late fall 1991.

Ob iectives

The objectives of this study were to:
I) Evaluate use of scales as a standard ageing method for Colorado squawfish.
2) Validate the scale technique by use of other bony structures and
mark-recapture information.
3) Determine average individual growth rates and compare between
populations.
4) Determine age composition of each population.
5) Compare rates of growth, size at maturity, and longevity in male and
female Colorado squawfish. .

Hypotheses were:
1) Colorado squawfish individuals can be aged using standard scale-ageing
techniques.
2) Ageing Colorado squawfish with scales is equivalent to ageing with
otoliths, vertebrae, fin rays, or opercula.
3) Growth rates are equal between individuals in different populations.
4) Growth rates of males and females are equal.
5) Current growth rates are equal to historical rates of growth.

Two objectives (2 and 5) were not met because of complications. Other bony structures
(otoliths, vertebrae, and opercula) were not used to validate the scale technique. An attempt was
made to age these structures, but my present expertise was not sufficient to place much
confidence in the results. Other validation methods, discussed later, were used to validate scale
ages. Work will continue with other bony structures, but ages obtained will also need verification
to ensure that ages are correct. Results of this work will be presented in my thesis. Because only
a limited number of aged fish were positively identified as either male or female, no attempt was
made to compare results between sexes.

METHODS

Canture and ta~ records

Records of Colorado squawfish tagged from 1978 through 1989 were obtained from the
database administrator of the USFWS Grand Junction, Colorado, field station. Additional records
were obtained from agency progress reports and personal com~unication with researchers.
Agencies involved in these collections included Bio/West, Inc.; Colorado Division of Wildlife;
Colorado State University; New Mexico Department of Fish and Game; New Mexico State
University; Utah Department of Natural Resources; and USFWS field stations in Grand Junction