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

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the number of populations specified and abundance requirement of 4,000 adult
fish proposed here for both downlisting and delisting are based on achieving
demographic stability. The abundance requirement originates from the
demographic life stage model results adopted by Lentsch et al. (1998), which calls
for 4,118 adult fish per population to achieve 95% probability of persistence and
maintaining existing genetic diversity.

The requirement for abundance trend duplicates what was proposed for
humpback chub and the natural annual recruitment requirement is similar to that
proposed for the razorback sucker, but uses the eight-year time frame used for
humpback chub. Also recognizing the lack of historical demographic data for the
bony tail, the natural recruitment criterion for this species can only be confirmed by
documentation of the population estimates and trend criteria. The ability to confirm
the presence of small-size bony tail in length frequency distribution data may be
constrained by difficulty in distinguishing its juvenile form from humpback and
roundtail chub juveniles when sampling habitats likely to contain these other Gila
species. Quantified measurements of recruitment rates necessary to maintain
these adult populations will have to be derived when any of the existing
populations appear to be self-sustaining.

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