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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Green River shows a similar decrease in recruitment from 23-27% to 5-9%, but is
distinguished by a subsequent increase to 19% in 1997. The White and Yampa
populations show similar recruitment attributes with rates fluctuating between 8-
16% and 8-22%, respectively, that are interspersed with single years of 0%
recruitment. Neither of these tributary populations demonstrates clear increasing
or declining trends in recruitment. Given the dependence of the White and Yampa
populations on recruitment from the Green River, increases in the small to mid-size
classes in the latter population would be expected to result ultimately in evidence
of increased recruitment to the tributary populations. This presumption is based on
the dispersal behavior noted by Osmundson et al. (1997).

Recovery Goals and Criteria Three populations are proposed as important to
recovery. These are the Green River, Colorado River, and San Juan River
populations. The presence of a Colorado pikeminnow population in all three sub-
basins is considered necessary, but only two of these three populations are
required to meet the criteria defined for abundance, abundance trend, annual
natural recruitment, and adult length frequency distribution for both downlisting and
delisting. The first two populations are further separated into population segments
with an associated distribution in major tributaries. These population complexes
reflect an interconnected system of linked population segments. For the Green
River complex, it is evident that adult populations reside in the four tributary rivers
and these populations join with the Green River adult population in producing the
larval progeny that drift into and grow to the juvenile stage in nursery habitats in
the mainstem Green River. These juvenile fish ultimately disperse, and recruit into
the adult populations. This dispersal and recruitment as adult fish maintain the
tributary populations in the Yampa and White rivers, and presumably in the _
Duchesne and Price rivers as well as the mainstem Green River population. In the
Colorado River, enhancement of the Gunnison River as a tributary population and
expansion into unoccupied mainstem habitat from Palisade toward Rifle are
recovery measures that would serve to increase population size and complexity
and contribute to demographic and genetic stability. The San Juan River
population is the smallest and most limited in habitat and habitat complexity (via
lack of access to large tributaries like the Animas River), but the persistence of a
very small Colorado pikeminnow population suggests recovery potential exists.
The uncertainty of this potential compared to the other two subbasin populations
makes application of population criteria more speculative, but the presence of a
population in the San Juan as a distributional requirement at least is appropriate.

Abundance goals must consider genetic viability through maintaining
effective population size (Ne). Franklin (1980) suggested an Ne of 500 animals
provides long-term maintenance of genetic diversity. Lynch (1996) indicated that
an Ne of 1000 was acceptable for long-term maintenance of adaptive genetic
variation. Even in long-lived animals such as these fish species with an estimated
survival rate of 0.86, it is unlikely that all individuals in a population contribute to
the next generation, therefore a greater number of adult fish are necessary to