Although fixed escapement policies have the strongest conservation potential, the
high variability in harvest levels can make fixed escapement less attractive to man-
agers and resource users than other options. However, in a world that increasingly
places multiple values on wildlife populations, including touristic, ecological, and
ethical values well beyond their immediate recreational or commercial hunting
value, fixed escapement policies seem likely to increase in attractiveness in the future.Most harvesting of wildlife for recreational hunting has been managed largely by trial
and error. This approach works well when populations and their habitats are good
at looking after themselves, when intrinsic rates of increase are high, when rate of
increase and density are related by tight density-dependent negative feedback, and
when the population size is kept above the level synonymous with the maximum
sustained yield (NMSY). These conditions describe what generally happens in tradi-
tional wildlife management. The populations and their habitats have been resilient
because it is only such animals that evolve into game species.
In practice, one cannot have both high density and high yield, except while den-
sity is temporarily being reduced. It cannot stay there for long because it will track
rapidly towards its equilibrium. Most managers seek to maximize offtake and so would
like to raise yield and lower density. This is the cause of the frequent clashes
between hunters and managers over whether females and young should be harvested.
In their review of harvest management for game birds, Robertson and Rosenberg (1988)
explain that “In America the potential harvest is assessed on an annual basis and the
activity of sportsmen controlled by bag and season limits. These restrictions rarely
aim to achieve MSY, partly due to the reluctance of sportsmen and managers to reduce
breeding populations, a situation often wrongly referred to as over-shooting.”
The results of this misunderstanding mostly kept offtake well below the maximum
sustained yield and game populations were seldom threatened by the harvesting.
However, the majority of sustained-yield estimates popular during the last few
decades were overestimates and would have resulted in extinction of populations had
they been applied rigorously.
The trick with managing a population for sustained yield is to play it safe. We esti-
mate MSY on what information is available to us (usually the trend of population
indices under a known constant offtake or constant effort), we refine that estimate
of MSY as often as we can or at least as often as our monitoring system allows, but
we keep the harvest well below the MSY. We make certain that our estimate of popu-
lation size remains well above the estimate of NMSY. Remember that in the early stages
of managing a population for sustained yield our estimate of both the current popu-
lation size Nand the NMSYmay be wildly inaccurate. Unless we have done this sort
of thing experimentally several times before we may not appreciate how inaccurate
our estimates are likely to be: we must allow ourselves a wide margin of error. Remember
that the standard error of an estimate tells us nothing about the accuracy of that
estimate. Our monitoring of population size will let us know in plenty of time when
we need to ease off harvesting effort.There is no difference in principle between harvesting for commercial benefit and
harvesting for recreational benefit. Both are based on the sustainable yield concept
suitably cushioned by a margin of error. However, in practice there are a number of
pitfalls to the management of sustained commercial offtake.346 Chapter 19