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

The success of any conservation or recovery program depends on eliminating or significantly
reducing the impacts of activities that threaten the species existence. It will be critical, therefore,
that the threats to the continued existence of Colorado River fish be eliminated in concert with
' attaining the IMOs. These threats have been categorized within the Endangered Species Act of
1973, as amended, as:
1) The present or threatened destruction, modification, or curtailment of its habitat or
' range,
2) Over utilization for commercial, recreational, scientific, or educational purposes,
3) Disease, predation, competition and hybridization,
' 4) The adequacy of existing regulatory mechanisms,
5) Other natural or human induced factors affecting its continued existence.
It would be appropriate for the UBRIP, therefore, to identify, categorize, and implement
management actions that specifically reduce the threats to a level that listing is no longer
warranted. In this fashion, recovery of the endangered Colorado River fish could be achieved:
' eliminate threats and attain IMOs.
Prioritization of Management Actions
Species specific life-history models have been used to prioritize management actions by identifying
' the life history stage most likely to be sensitive to conservation efforts. The National Research
Council (NRC 1992) used a life stage model to conclude that protection of juvenile and sub-adult
sea turtles would enhance population status to a greater degree than protecting eggs and hatchlings
' from human induced mortality. Lande (1988) conducted an similar analysis on northern spotted
owl by comparing population growth to a variety of demographic parameters and concluded that
annual adult survivorship was the most critical parameter followed by juvenile survivorship, and
fecundity.
We used the Crowl and Bouwes (1998) life-stage model to evaluate the influence of enhancing the
critical demographic parameters of the four endangered Colorado River fish species. The purpose
of this evaluation was to identify which life-stage parameters are most sensitive to management
actions. Simulations were run to determine how changes in each of the survivorship values for
each stage class affected the time it took for squawfish to reach some chosen target value. For
these simulations, we used an initial population of 1400 (representing the Upper Green) and a
population target of 5000 adults for illustrative purposes. Two results are important for these
' kinds of simulations. First, a comparison of the percent increase required for each life stage
provides insight into how management actions might be prioritized. Figures 3 and 4 show that to
reach the target adult population of 5000 (beginning with 1400), increases in survivorship of 12,
17.5, 37, 49, 73 and 841/o would be required for egg, YOY, 1-, 2-, 3-yr old and adult life stages,
respectively. For these results, increasing egg or YOY survivorship by relatively small
' percentages (12 and 17.5%) results in the population reaching the target value. In contrast, to
increase the squawfish population from 1400 to 5000 adult individuals requires increasing
survivorship values by 37, 49, 73 and 84%, potentially difficult targets to reach. The second
' criteria by which to prioritize management activities is the time required to reach the target values
for various activities. Figures 3 and 4 show that very small increases in survivorship values (2%)

23