Game harvesting comes in two forms: game ranching (or game farming) and game
cropping. The difference is in degree rather than kind, but essentially game ranch-
ing seeks to bring the animals under human control, as in the farming of domesti-
cants, whereas game cropping is the harvesting of wild populations. Game ranching
is a spectrum of activities that overlap conventional animal husbandry at one end
(e.g. the reindeer industry in Finland and Russia) and game cropping at the other
end. It is beyond the scope of this book. The interested reader might try papers in
Beasom and Roberson (1985) and Hudson et al. (1989) for a general overview of
game ranching, and the volume edited by Bothma (1989) for a thorough treatment
of game ranching in southern Africa. Because game cropping can be an important
conservation threat, however, we consider it in greater detail below.
In large mammal species, harvesting is often directed at males rather than females
or focused on older rather than younger age groups. This is often imposed through
tag or license restrictions on hunters. The intent of such a policy is to guarantee the
perpetuation of the breeding segment of the population. Age- and sex-structured har-
vest models of Norwegian moose, for example, suggest that the optimal policy would
be to concentrate harvests on calves and old males, while rarely removing females
from the population (Sæther et al. 2001). This makes intuitive sense, if the popula-
tion is well mixed and all harvested individuals are equally valuable.
Male-biased harvesting is not always the best policy. In Scottish red deer, for
example, the proportion of males born tends to decline with population density, and
the mortality of older animals increases relative to females (Clutton-Brock et al. 2002).
As a result, red deer populations have naturally skewed sex ratios, even without
sex-biased hunting. But males bring in far more income to landowners than do females,
so highly skewed sex ratios are economically disadvantageous. The remedy is
increased culls of females to keep female density less than 60% of the ecological
carrying capacity (Clutton-Brock et al. 2002). In other species, extreme male-biased
culls could lead to some females being unable to conceive (Ginsberg and Milner-Gulland
1993; Milner-Gulland 1997), obviously outweighing any slight advantage accruing
from age-biased harvesting.
In order to develop sex-biased harvest models, however, detailed information is
required on age- and sex-specific survival rates, reproductive rates, and how these
demographic parameters are affected by changes in population density. The last point
is crucial: without reliable information on density-dependent parameters, even
though detailed life tables are available, a prioriidentification of optimal harvesting
levels is impossible. The requisite demographic information is available for few
wildlife species, so male-biased harvests should be viewed with an appropriate
degree of caution.
In addition to the biological complexities inherent to renewable resource systems,
there are additional complicating factors when wildlife species are harvested com-
mercially. This is because market dynamics, limitations on harvest controls, and poten-
tial conflict between short-term versus long-term goals also influence the levels of
harvest effort. This has important effects on the economic equilibria for effort levels
and the risk of resource overexploitation. For example, imagine that a population has
a carrying capacity K=100 individuals, maximum intrinsic growth rate rmax=1, catch-
ability coefficient q=0.02, and effort E=20 units. Annual net recruitment (R(N))
WILDLIFE HARVESTING 347
19.7 Age- or sex-biased harvesting
19.8 Bioeconomics
