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
t
I
I
I
I
I
I
I
I

flannel mouth sucker (1000/mi), resulting in an endpoint objective of 100 razorback
sucker/mile (Ryden 1997, Ryden and Pfeifer 1994). The Colorado and San Juan
razorback sucker stocking plan objectives will clearly exceed the minimum
population abundance necessary to maintain an effective population size (Ne) if
they are successful. The Utah stocking plan will achieve the minimum population
abundance required to maintain Ne for razorback sucker in the Green River
according to the demographic life stage model employed by Lentsch et al. (1998).

With the lack of historic population data to ground recovery goals, the
abundance requirements of the recovery plan and the Utah and Colorado stocking
plans are arbitrary at this time. Limitations upon the carrying capacity of the
Green River or any of the other rivers recommended for razorback sucker
populations are primarily a lack of lentic, floodplain habitat for nursery or adult
residence purposes, and the presence of an abundant nonnative fish population
acting as predators and competitors. Which of these factors that act as the
primary limiting factor is uncertain. Implementation of stocking plans, floodplain
habitat restoration and nonnative fish control actions must proceed to establish
adult razorback sucker populations, determine realistic abundance criteria and
refine recovery goals for this species. At this time it is proposed to define five
prospective recovery populations including Lake Mojave as an artificially
maintained genetic refugia population, two riverine populations in the middle and
lower Green, and two populations in the Colorado-Gunnison and San Juan rivers
(Table 5). It is proposed to require the Lake Mojave, middle Green River, and one
of the other populations to meet the abundance requirement of 5,400 fish for
downlisting. A fourth population in addition to the the downlisting population would
have to meet the abundance criterion for delisting.

The USFWS Recovery plan further specifies a general abundance trend
requirement of maintaining of a threshold abundance for five years for all
razorback sucker populations under both downlisting and delisting criteria. It is
proposed here to further specify what "maintenance" means by using the same
regression slope criterion for Colorado pikeminnow of six population estimates
spanning 12 years for delisting (Table 6).

No quantifiable criterion describing natural annual recruitment in razorback
sucker populations can be specified due to a lack of historic or present examples.
The USFWS recovery plan specifies that the abundance levels required for
downlisting and delisting for all populations be maintained by natural recruitment
for ~5 years. It is proposed here to amend this requirement to five years for
downlisting and 12 years for delisting. This natural recruitment criterion can only
be confirmed by documentation of population estimates meeting the abundance
and trend criteria and the presence of small razorback sucker in length frequency
distribution data that cannot be attributed to stocking. Quantified measurements of
recruitment rates necessary to maintain these populations will have to be derived
when any of these existing populations appear to be self-sustaining.

35