Quota setting
It is not necessary to know the numbers of animals in the population
in order to set sustainable quotas – indeed a system based on
population estimates is likely to be far less robust than an
adaptive management system (Holling 1978, Bell 1986, Martin
1999)The key parameter to be monitored is the age of trophies
taken from the population. (See
adaptive quota setting for buffalo for more details). Methods
of ageing roan, sable and tsessebe from their dentition or horns
are available (Grobler 1979,1980; Joubert 1976; Child et al
1972; Huntley 1973), which could easily be applied by local
community monitoring staff with some training. It is logical
that conservancies should take on this monitoring rôle in all
areas where the species are hunted in conservancies since it
is effectively their resource being managed. In State protected
areas where there is hunting this would be the responsibility
of park staff.
Assessing population numbers based
on monitoring data from sport hunting
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Figure 23: Effects of hunting quotas
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The adaptive monitoring system can be reversed to provide
population estimates based on the monitoring data obtained
from sport hunting. The data in (Figure
23) show the shape of the age pyramid to be expected at
different levels of hunting quotas. For example, if the hunting
quota is 2% there are unlikely to be any males older than
8 years in the population. If the ages of the animals taken
in any year are accurately determined and if it is found that
there are 7 year-old animals in the population but no 8 year-olds,
one can assume that the actual numbers of animals killed in
the year concerned is 2% of the population. This permits a
reverse calculation to be carried out: if 10 animals were
hunted and this, according to the age structure model should
be 2% of the population, then total population would be 500
animals. The system is based on the following assumptions:
- the adult male survival rate and the selectivity for
trophies are close to the values used in the model and
- the age determinations can be carried out with some accuracy
However, over several hunting seasons through some iterations
with the model and through deliberately pursuing a course
of active, adaptive management, it might be possible to simultaneously
refine the model, obtain better estimates of the populations
from which the hunting trophies are derived and arrive at
optimum hunting quotas.
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