9378

• UCREFRP Catalog Number: 9378
• Author: Nesler, T. P.
• Title: Recovery of the Colorado River Endangered Fishes
• USFW Year: 2000.
• USFW - Doc Type: Biological recovery goals and criteria for Colorado pikeminnow, Humpback chub, Razorback sucker & Bonytail.
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

Razorback sucker

Status and Trends The status and trend of this species is evident in the
disappearance or decline of riverine populations (USFWS1998). The information
available for this species shows it's range and abundance has declined such that
only one wild riverine population and one reservoir population of any numerical
significance remain (middle Green River and Lake Mojave). Recruitment in the
middle Green River population appears inadequate to stabilize abundance (Modde
et al. 1996) and recruitment in the Lake Mojave population is sustained through an
on-site spawning and growout operation for augmentation stocking back into the
reservoir (Mueller 1995). It is clear that recovery of the razorback sucker from its
current federal status as endangered will require restoration stocking to develop
adult populations, and mitigation of existing threats to enable reproductive success
and self-sustaining natural recruitment. Available historic data was inadequate to
provide a specific assessment of population abundance, trends, recruitment and
size structure similar to the Colorado pikeminnow and humpback chub.

Recovery Goals and Criteria Historical population demographic data for a
viable, riverine population of razorback sucker is unavailable to use as a template
for recovery goal development as was done for the Colorado pikeminnow and
humpback chub. The recovery plan (USFWS 1998) calls for five populations for
downlisting and seven populations for delisting. With the exception of the Lake
Mojave population, the remaining populations must be maintained by natural
recruitment. The genetics management plan for Upper Basin (Czapla 1999)
identifies three presumptive populations, including the Middle Green River, Lower
Green River, and Upper Colorado River. For the purpose of identifying recovery
goals and criteria, these two guidance documents are different only in their degree
of specificity concerning populations identified.

The recovery plan identifies populations necessary for recovery specifically
in Lake Mojave, the middle Green River, and the lower Green River. The genetics
management plan for the Upper Basin goes one step further in identifying the
Upper Colorado River as a targeted population. The recovery plan recommends
five potential population sites upon which to achieve the recovery goal of four
razorback sucker populations additional to the three identified. These include the
Salt and Verde rivers in the Lower Basin, and the Colorado, Gunnison, and San
Juan rivers in the-Upper Basin. Presently, restoration stocking of razorback sucker
has occurred in the San Juan, Verde, Salt, and Gunnison rivers. At this time,
hatchery-reared razorback sucker have survived and reached reproductive status
in the San Juan River (Ryden 2000). Fish stocked in the San Juan River were
progeny derived from adults collected in the San Juan River arm of Lake Powell.
Fish stocked in the Gunnison River were derived from adult razorback sucker from
the upper Colorado River, Etter Pond (near Palisade, Colorado) and the Colorado
River arm and San Juan River arms of Lake Powell. The direction of genetics
management for razorback sucker is to maintain Upper Basin and Lake Mojave
stocks separately, and to maintain Green River stocks separately from the

33