The Sonoran pronghorn is one of five subspecies of pronghorn (see Example 14.2).

Question

The Sonoran pronghorn is one of five subspecies of pronghorn (see Example 14.2). The Sonoran subspecies is restricted to approximately 44,000 hectares in southwestern Arizona. There were approximately 200 individuals in this population based on census estimates in the 1990s. A group of 22 biologists from a variety of federal, state, tribal, university, and environmental organizations convened a population viability analysis (PVA) workshop in September 1996 Estimates of the life history parameters used by VORTEX were provided by participants of the workshop. Some of the values were available from field data, but there were no quantitative data available for many parameters. For these parameters, the field biologists provided "best guesses". The participants performed a sensitivity analysis to evaluate the response of the simulated populations to uncertainty by varying eight parameters: inbreeding depression, fecundity, fawn survival, adult survival, effects of catastrophes, harvest for research purposes, carrying capacity, and size and sex/age structure of the initial population. A severe drought in 2002 nearly caused the extinction of this subspecies. Eighty percent of the population was lost, from an estimated 100 animals down to a low of 21. There is concern that this bottleneck may have caused substantial loss of genetic variation so that this population may no longer be viable. Some have suggested that "genetic rescue" may now be appropriate. That is, animals from other subspecies should be introduced into the Sonoran subspecies. Do you think that introducing pronghorn from another subspecies is a good idea? Discuss the potential advantages and disadvantages of this management action. Your specific recommendation is less important than whether or not you consider and discuss the most important issues involved.

Explanation / Answer

Sonoran Pronghorn;
It is known as "prairie ghosts" because they are so elusive, the Sonoran pronghorn is the fastest land mammal in North America.

Pronghorn look like a cross between antelopes and goats but are actually neither. Their closest living relatives are, strangely enough, giraffes, but all other members of their taxonomic family are extinct. The Sonoran pronghorn is the fastest land mammal in North America, with top racing speeds of more than 95 kilometers per hour.

Smaller and lighter in color than other pronghorn subspecies, the genetically and geographically unique Sonoran pronghorn is specially adapted for survival in harsh arid conditions. Sonoran pronghorn are reddish brown on their backs and sides, and have lighter colored undersides. They have bright white markings on their heads and necks; males have black faces and black patches on the sides of their necks. Male Sonoran pronghorns sport large black pronged horns, while females have short black horns.

Pronghorn were once as widely distributed as buffalo. The desert ranging pronghorn, including the Sonoran pronghorn, ranged widely but in reduced numbers within the Sonoran desert in Arizona and California down into Sonora, Mexico – a broad, open desert landscape with limited vegetation. Today they are reduced to an estimated 160 free ranging animals within the United States, and an additional 240 free ranging within Sonora Mexico.

RECOVERY STRATEGY
The recovery strategy is to secure a sufficient number of Sonoran pronghorn populations that are
viable under appropriate management scenarios within select areas throughout their historical
range. In recognition of the binational distribution of the species, and the unique challenges and
opportunities this presents, two conservation units (CU) for the species have been designated,
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one in the United States and one in Mexico. The U.S. Conservation Unit is located in Arizona
and California and includes the historical range of Sonoran pronghorn in the United States. The
Mexico Conservation Unit includes the historical range of Sonoran pronghorn in Mexico. Within
these CUs there are management units, including the Cabeza, Arizona Reintroduction, and
California Reintroduction Management Units in Arizona and California; and the Pinacate,
Quitovac, and Sonora Reintroduction Management Units in Sonora.
RECOVERY GOAL, OBJECTIVES, AND CRITERIA
The recovery goal is to conserve and protect the Sonoran pronghorn and its habitat so that its
long-term survival is secured, and it can be removed from the list of threatened and endangered
species (delisted). To achieve this goal, this draft recovery plan identifies the following
objectives:
1. Ensure multiple viable populations of Sonoran pronghorn rangewide.
2. Ensure that there is adequate quantity, quality, and connectivity of Sonoran pronghorn
habitat to support populations.
3. Minimize and mitigate the effects of human disturbance on Sonoran pronghorn.
4. Identify and address priority monitoring needs.
5. Identify and conduct address priority research needs.
6. Maintain existing partnerships and develop new partnerships to support Sonoran
pronghorn recovery.
7. Secure adequate funding to implement recovery actions for Sonoran pronghorn.
8. Practice adaptive management, in which recovery is monitored and recovery tasks are
revised by the Service in coordination with the Sonoran Pronghorn Recovery Team as
new information becomes available.

Reintroducing species:
Any process to reintroduce a threatened or endangered species as “experimental” requires the Service
to:
Compile and analyze all new biological information, including habitat requirements, on the
species;
Review the overall approach to the conservation and recovery of the Sonoran pronghorn in the
United States;
Review actions identified in the recovery plan;
Determine what areas, if any, might require special management or areas that should be
excluded from the experimental population area;
Write a draft environmental assessment and present alternatives to the public for review and
comment;
Review and incorporate any new information or analyses provided through the public input;
Publish a proposed rule in the Federal Register and solicit comments from the public; and
Finalize the environmental assessment and the rule designating an experimental population and
identifying an experimental population area; thereby either authorizing the release of a species
as experimental or adopting the no action alternative (not permitting the release).

Benefits of reintroducing species:
Reintroductions aid in the recovery of threatened or endangered species. Species with small
populations and limited ranges tend to be more vulnerable to perturbations. The Service augments
species’ existing population numbers in a variety of situations around the country. When a species’
range has been severely reduced or a significant population extirpated, and we believe the species
needs a wider distribution than the current one to achieve the long term resilience and persistence
necessary for recovery and delisting, often the only remaining recovery option is reintroduction.
Under a section 10(j) rule, the Service has much more leeway to take local concerns into account when
preparing management strategies and thus can avert restrictions on current and future land uses and activities. This flexibility can make a reintroduction process more acceptable to apprehensive
stakeholders. The reintroduction process, by its nature, is very inclusive. The Service has seen stronger
support for conservation efforts when stakeholders are involved and have a voice in the process.

Why reintroduce new Sonoran pronghorn populations :

Historically, both the numbers and range of Sonoran pronghorn in the U.S. and northern Mexico have
been severely reduced due to a combination of human activities and natural occurrences. In the drought
of 2002, there was a major die off on both sides of the border and the remaining U.S. population was
reduced by 83 percent to only 21 animals. A captive breeding facility was established at Cabeza Prieta
NWR in 2003 and the Service and its partners have worked to increase the availability of emergency
water sources and forage for Sonoran pronghorn.
Consequently the U.S. wild population now stands at 80-90 individuals. However, this population
remains both small and restricted in range, making it vulnerable to drought, wildfires, the genetic and
demographic problems associated with small populations and a variety of human-caused disturbances.
The Service and the Sonoran pronghorn recovery team believe that reestablishment of two additional
populations in its historic range will significantly reduced the likelihood of extinction and contribute to
the resiliency and persistence necessary to recover Sonoran pronghorn so that they no longer need the
protections of the ESA and can be delisted

The recovery goal is to conserve and protect the Sonoran pronghorn and its habitat so that its long-term survival is secured, and it can be removed from the list of threatened and endangered species .

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