9690

• UCREFRP Catalog Number: 9690
• Author: Recovery Implementation Program
• Title: Recovery Implementation Program For Endangered Fish Species In The Upper Colorado River Basin 23rd Annual Recovery Program Researchers Meeting
• USFW Year: 2002
• USFW - Doc Type: 21
• Copyright Material: NO

morphologically variable cyprinid species native to the Colorado River drainage. All three
members of this complex, G. cypha, G. elegans, and G. robusta occur (or occurred) in the Yampa
River Canyon. Both G. elegans and G. cypha are federally listed as endangered, with the former
likely extirpated from the Yampa River; only G. robusta is still unlisted and relatively common
although it is a candidate for listing. Growth rates based on valid age determinations, as well as
other life history aspects, are poorly known for G. robusta, and indeed for all three species.
Consequently, in addition to providing information directly on G. robusta, this species may be
considered a surrogate to better understand growth patterns of G. elegans and G. cypha. Gila
robusta have been collected during July in 1998, 1999, and 2001 by angling (1998) and
electro fishing (1999, 2001) in the Yampa River Canyon in Dinosaur National Park. Presumed
ages determined from otoliths, opercle bones, and scales all show significant correlations.
However, otoliths and opercles show the highest correlations. Compared to both otoliths and
opercle bones, scales underestimate ages for fish greater than seven years. Based on data from
1999 (n=28), median ages were 6, 6, and 5, and maximum ages were 18, 11, and 8, based on
otoliths, opercles, and scales, respectively. Using otolith data, growth trajectories of males and
females diverge for fish older than 10 years, with females showing greater increases in length and
mass than males.

Snyder, D. E.

Larval Fish Laboratory, Colorado State University, Ft. Collins, CO

Computer-Interactive Key to Sucker Larvae and Early Juveniles of the Upper Colorado
River Basin. The detailed descriptions and 60 pages of keys in the Colorado Division of Wildlife
(CDOW) guide to Upper Colorado River Basin sucker larvae and early juveniles (Snyder and
Muth 1990) have served the Recovery Program and research community well, but they need to be
updated with character range extensions observed since publication and expanded to include
longnose sucker. However, intricate printed keys such as these are very difficult to prepare,
correct, update, or expand to cover additional species because each change cascades through
most subsequent portions of the key. Also, users of the very long and intricate keys have found it
formidable and inflexible. As a modem alternative, I've decided to replace the printed key with a
computer-interactive key because it is much easier to prepare, update, and expand, and users will
find it a much more flexible and user-friendly taxonomic tool. Among other advantages, users can
limit consideration to a subset of species when appropriate and bypass characters that are
unfamiliar, difficult to accurately measure or observe, or that happen to be damaged on the
specimen of concern. With this presentation I will discuss and demonstrate a preliminary version
of the new key.

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