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

1

1

1

1
1

1

1
QUANTIFIABLE INTERIM MANAGEMENT OBJECTIVES
The establishment of quantifiable interim objectives is critical for the management and recovery of
endangered species in the Colorado River system. The term "interim" is being used here because
the current objectives established for the UBRIP will need to be refined at regular intervals as new
information is acquired. The quantified objectives presented herein (Table 7), therefore, do not
imply any priority for use by the USFWS down-listing species. In addition, the achievement of
these objectives is dependent upon a multitude of environmental conditions (see below) and
management actions. These management actions have been outlined and are reviewed annually by
the UBRIP in a recovery action plan. The application of IMOs will primarily be within the UBRIP
to evaluate progress towards recovery of these endangered fish. In this light, the IMOs will
provide a framework for prioritizing short-term actions needed for recovery and guidelines for
obtaining the information needed to define quantifiable long-term recovery objectives.
The calculated IMO values for each species included: 5477 (±966) for Colorado squawfish, 5316
(±804) for razorback sucker, 4796 (±1317) for humpback chub, and 4118 (±817) for bonytail
(Table 7). The values represent the total number of adults required to reach a 95% probability of
maintaining Ng adults for at least 100 years. The values were driven largely by the relatively low
fecundity estimates and low young-of-the-year survivorship values (Crowl and Bouwes 1998).
They appear, however, to be reasonable. Nunney and Campbell (1993) indicate that minimum
viable population sizes of up to 10 times N. would be reasonable. They argue that this magnitude
of population size would be required to preserve small differences in life history and behavior traits
between populations. Our estimates of N. are 5.5, 5.3, 4.8 and 4.1 times greater than N. for
Colorado squawfish, razorback sucker, humpback chub, and bonytail, respectively. By targeting
increased survivorship at specific (earlier) life-stages, these estimates could decrease significantly.
The life-stage distribution of individual species based on current values are summarized in Table 8.
Table 8. Life-stage structure for each population based on management objective values.
Age
class CS RZ BB BT
Age
class Surv
- % #/yr Surv
% #/yr Surv
% #/yr Surv
% #/yr
Adults 80 5477 70 5316 76 4796 80 4118
Age-3 60 9128 55 7594 76 6311 60 5148
Age-2 40 22821 37 13808 15 8303 40 8579
Age-1 30 76069 22 37318 10 55355 30 21448
Age-0 14 543353 14 169629 5 553555 14 71493
Eggs 1 54335317 1 1211635 1 11071099 1 510665
22