8033

• UCREFRP Catalog Number: 8033
• Author: Lentsch, L. D., et al.
• Title: Endangered Fish Interim Management Objectives for the Upper Colorado River Basin Recovery And Implementation Program -Final Report.
• USFW Year: 1998.
• USFW - Doc Type: 55,
• Copyright Material: NO

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DEVELOPMENT OF QUANTIFIABLE OBJECTIVES
Objectives for management of endangered fish in the UCRB were quantifiable in terms of viable
population size estimates. They represent the number of individuals in a population (N.) that the
UBR1P should target to achieve through recovery management actions. They are the population
size estimates of the IMOs. These estimates incorporate two basic biological components:
maintenance of genetic variability (expressed as NJ and population demographic stability
(incorporated within N.). The process used to develop the IMOs was based upon a review of a
number of methods for quantifying population status, minimum viable population size, listing
criteria, and conservation criteria (Soule 1987, Mace and Lande 1990, Nunney and Campbell
1993, Ralls et al. 1996, Allendorf et al. 1997). This approach incorporated: 1) the conceptual
technique for developing delisting criteria for sea otters outlined in Ralls et al. (1996), 2) the
application of the empirical information for measuring effective population sizes for Pacific salmon
stocks as suggested by Waples (1990a,b and 1991), 3) the methods for calculating populations
parameters important for prioritizing recovery efforts by Allendorf et al. (1997), and 4) the
methods for establishing listing criteria by Mace and Lande (1990). The acceptable level of risk
for long-term viability was set at a 95% (1 in 20) chance of persistence for 100 years.
Process and Assumptions
The following process was adhered to for each species and their representative subpopulations in
the UCRB. First, the number of populations or subpopulations was identified. Second, a
minimum effective population size (M), was set as a constant for all populations. Third, sex ratio
was estimated based on empirical evidence and varied from species to species. Fourth, the number
of individuals breeding in the population (Nb) required to maintain N. was estimated based on sex
ratio. Fifth, the ratio of effective population size to census population size (NA?) was set as a
constant for all populations. Sixth, the number of individuals in the population required to maintain
the genetic diversity (based on Nb and NJM (NJ was estimated. The seventh and final calculation
involved accounting for the population demographic features by using Crowl and Bouwes (1998)
life-stage models.
Accurate empirical information did not exist to calculate N. for all populations and species. To
estimate the required values to calculate N. we conducted a literature review, a technical
workshop, and consulted the Biology Committee for the UBRIP. The literature review included a
search for information on the target species as well as for "surrogate" species that may have similar
life history traits. Species experts from the UCRB participated in the workshop and are members
of the Biology Committee. They reviewed the values of parameters set in the Crowl and Bouwes
(1998) life-stage, reviewed the existing information, and came to agreement on the final values
used in the N. calculations for each species (Table 6). They also agreed to the use of "surrogate"
species information for bonytail. The sex ratio for bonytail was assumed to be the same as
humpback chub and the population demographic values were assumed to be the same as Colorado
squawfish. This assumption was made because no empirical information exists in the Upper Basin
for bonytail (Table 4).
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