9383

• UCREFRP Catalog Number: 9383
• Author: SWCA, I.
• Title: Recovery Goals for the four Colorado River Endangered Fish Species.
• USFW Year: 2000.
• USFW - Doc Type: Logan.
• Copyright Material: NO

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1997), bald eagles, peregrine falcons, desert tortoise (Berry 1999), Pacific salmon (Allendorf et
a 19 , and southern sea otters (Ralls et al. 1996).
urthermore, recovery is based on removal of threats and improvement of the status of
the species during the period in which it is listed, and not just from the time a listed species is
proposed for reclassification. Hence, while dams were considered a major threat to the four
endangered fishes of the Colorado River, construction of new dams in prime habitat ceased
nearly 4 decades ago. The ongoing threat is not new dam construction but the effects linked to
the operation of th s, such as river regulation, cold water releases, and removal of
sediment and org tter, as well as introduction of nonnative fish species.
Two major stan ards must be met before achieving recovery of an endangered species.
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The first is the determination and quantification of the population at the level of "endangered",
which is defined in the ESA (Section 3 [6] and 3 [20]) as "...a species which is likely to become
extinct throughout all or a significant portion of its historic range." The second is the
determination and quantification of the population at the level of "threatened", which is defined
in the ESA as "...a species which is likel become an endangered species within the
foreseeable future. "
To determine the level at which a species is "endangered", the standard suggested by
Mace and Lande (1991) is used, in which a vertebrate population with an effective population
size (Ne) of <500, that may be subject to catastrophic population crashes, should be considered in
danger of extinction and therefore, endangered. A species is in danger of extinction when any of
the following considerations and conditions is met:
. Genetics: when numbers of individuals are to to maintain genetic variability
and to counter the effects of deleterious gene mutations from inbreeding.
. Demographics: when numbers of individuals are too low so that when deaths
exceed births and recruitment for periods of time, the population moves toward
low genetic viability and extinction.
. Population Redundancy: when populations are too few, or too concentrated, to
avert catastrophies from singular threats.
. Threats: when threats persist such that a significant portion of the po tion can

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