|
- problem animal control - harvesting
- Illegal hunting -
It is assumed that sport hunting, problem
animal control and harvesting
will be the main forms of hippo management in the Caprivi.
Sport Hunting
At the outset, it is assumed that sport hunting will
be restricted to male hippo. Hunting clients seek trophies
with large canines and large body size and these characteristics
are limited to males. The canine teeth of a hippo begin
to assume full size at about 20 years of age (approximately
2kg for the pair) and only increase slightly over the
remainder of the hippo's life. The largest weights seldom
exceed 3kg and, in some cases, the teeth may decrease
through breakage and wear (Laws 1968). The body weight
of a 20 year old hippo is about 1,250kg (Analysis
2) and hunting clients are unlikely to shoot much
smaller animals.
The proportion of a hippo population which can be sustainably
hunted to provide trophies is as low as that for elephant.
If it is assumed that the earliest age at which hippos
are likely to be taken as trophies is about 20 years
of age, this restricts hunting to less than 7% of the
total population. This is not the important statistic,
however. In a population of 1,000 animals the annual
recruitment to the 20 year old age class is about 7
animals and it is this figure which cannot be exceeded.
However, if quotas were set as high as this, all males
older than 20 years would be removed from the population
and hunting would be reduced to the annual recruitment
of 20 year olds. Martin tested the effects of increasing
levels of hunting quotas on the age structure of a hippo
population (Analysis
8; Figure
17 ) using a population
model.
The maximum sustainable offtake of male hunting trophies
from a hippo population is about one-half a percent
of the total population. At this level, there will always
be some males in the population surviving beyond 20
years of age (Figure
18D). A slight selectivity for older animals with
larger tusks is built into the model (Analysis
8).\
Hunting causes the stable age structure of the population
to become slightly skewed in favour of females (males:females
48%:52% versus 49.9%:50.1% when there is no hunting).
The number of males in the age classes below 20 years
actually increases from the number in the unhunted population
(Figure
17) but this is purely an artefact based on the
redistribution of the animals in all the age classes
to fit the new population profile. The total number
of males in a population of 1,000 animals decreases
from 494 in the no-hunting situation to 463 when it
is attempted to extract a quota of 0.9% (9 animals)
from the population.
It is sound management strategy to maximise the number
of hippo which can be hunted as trophy animals since
this is the highest valued use for a hippo. When setting
multiple quotas (i.e. sport hunting, problem animal
control and harvesting), the sport hunting quota should
be set first and the others adjusted to take up the
balance of the sustainable offtakes.
back to top
Problem animal control
Under a management strategy to maximise returns from
a hippo population, it makes little difference whether
a hippo is killed under the heading "problem animal"
or "harvest" - provided the products of the hippo (meat,
skin and teeth) are recovered efficiently and sold or
used to maximum advantage. However, the contingency
may well arise of having to deal with a problem
animal and this would take precedence over any harvesting
programme. Martin proposes a quota of 10 problem animals
(1% of a population of 1,000 animals) and animals should
be killed as problem animals only when absolutely necessary.
At the end of the management year any balance left on
the PAC quota can be harvested.
For the purpose of simulating the effects of problem
animal control (PAC) in the population
model it has been assumed that PAC is limited to
animals older than 5 years and that both males and females
are included without selectivity for larger animals.
Using the same model
parameters as for sport hunting tests, it was found
that the maximum sustainable offtake of problem animals
is slightly under 6% of the total population (Table
1). In a population with a stable age structure, about
59% of the total population consists of animals older
than 5 years and the annual recruitment into the 6 year
old age class is slightly less than 6% of the total
population. Removing 5% of the population as problem
animals has the effect of narrowing the upper part of
the age pyramid and broadening the base (Figure
18C).
|
|
PAC
offtake - % of total population
|
|
|
0
|
0.25
|
0.5
|
0.75
|
1
|
2
|
3
|
4
|
5
|
6
|
| |
|
|
Rate
of growth %
|
7.13
|
6.82
|
6.51
|
6.20
|
5.90
|
4.65
|
3.45
|
2.25
|
1.00
|
Unsustainable
|
|
Initial
population 1,000
|
PAC
offtake - number of animals
|
|
|
65
|
70
|
80
|
90
|
100
|
150
|
200
|
|
%
of population at start
|
6.5
|
7
|
8
|
9
|
10
|
15
|
20
|
| |
|
|
Years
to extinction
|
46
|
34
|
23
|
18
|
15
|
8
|
5
|
|
Analysis 2: Relationship between age and body weight
for hippo
Analysis 7: Financial value of hippo
Analysis 8: Effects of trophy hunting quotas on age
structure
Figure 17: Effect of increasing sport hunting quotas
on population age structure
Figure 18 Effect of various management practices on
hippo population age structures
|
These relatively high offtakes of problem animals are possible
only if the assumption that both males and females are hunted
in equal proportions is satisfied. If it is satisfied, it
has the further effect that sport hunting quotas are not affected
by the level of problem animal control - provided it is sustainable
(Figure 18E).
If the assumption is not satisfied and more males than females
are killed as problem animals, then sport hunting quotas would
have to be reduced to compensate for this effect.
back to top
Harvesting
If harvesting (cropping) of hippo is to take place, it is
strongly recommended that it is practised unselectively. Any
cropping system which targets particular age classes will
alter the age structure of the population in a manner which
may produce undesirable long term effects. It has already
been shown that by excluding the first five age classes from
PAC the age pyramid assumes a 'bottom-heavy shape' (Figure
18C) and by selectively hunting large males for trophies the
age pyramid becomes skewed in favour of females and has a
'bite' out of it for all the male age classes above 30 years.
If any further selective pressures are introduced through
harvesting it becomes increasing difficult to predict the
outcomes.
For a hippo population
growing at 7.13% per annum, offtakes of up to 7% of the
total population are possible, provided the harvest is unselective
(see table below). For a population of 1,000 animals, the
maximum sustainable harvest would be about 70 animals annually
if there were no sport hunting or problem animal control.
At this level, population growth would effectively be zero.
The age structure of the harvested population is identical
to that of the unharvested population (Figure
18A & B).
|
|
Harvesting
– % of total population
|
|
|
0
|
0.25
|
0.5
|
0.75
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
| |
|
|
Rate
of growth %
|
7.13
|
6.87
|
6.60
|
6.33
|
6.07
|
5.00
|
3.99
|
3.00
|
1.78
|
0.71
|
0
|
|
Initial
population 1,000
|
Harvest
annual offtake – fixed number of animals
|
|
|
71
|
75
|
80
|
90
|
100
|
120
|
150
|
200
|
300
|
500
|
|
%
of population at start
|
7.1
|
7.5
|
8
|
9
|
10
|
12
|
15
|
20
|
30
|
50
|
| |
|
|
Years
to extinction
|
59
|
40
|
32
|
24
|
19
|
14
|
10
|
7
|
5
|
3
|
When harvesting is combined with problem animal
control and sport hunting, the maximum
harvest must be reduced. If 5 sport hunting trophies are taken
annually from the population of 1,000 animals in the Caprivi
(0.5% of the total population) and if 10 animals are killed
as problem animals (1% of the total population), then the
maximum harvestable balance which would result in zero population
growth would be about 45 animals. The age structure which
results from this management regime is shown in Figure 19F.
To implement such a management programme in the Caprivi is
not as simple as it might appear. Firstly, the Caprivi hippo
population is dispersed in a number of geographically discrete
subunits on the different rivers in the Caprivi. Secondly,
on those river sections which are international boundaries
the Namibian 'share' of the hippo population should strictly
be treated as half of the estimate for any particular section
- it would be provocative to neighbouring countries to treat
it as more than this. Thirdly, to harvest with no bias towards
any particular age class requires the application of random
number techniques and some discipline. Lastly, some practicalities
need to be taken into consideration in allocating quotas in
conservancies.
Martin simulated the application of the management principles
(Table 7).
|
|
Total Population
|
Namibia
population
|
Sport Hunting
|
Problem
Animal Control
|
Harvest
|
Total Offtake
|
|
|
C
|
A
|
C
|
A
|
C
|
A
|
|
|
Kavango
|
247
|
247
|
1.2
|
1
|
12.4
|
1
|
12.4
|
12
|
14
|
|
Mahango
NP &
Babwata
Western Core
|
187
|
187
|
0.9
|
1
|
9.4
|
|
9.4
|
9
|
10
|
|
Communal
land
|
60
|
60
|
0.3
|
|
3.0
|
1
|
3.0
|
3
|
4
|
|
Kwando
|
308
|
234
|
1.2
|
2
|
11.7
|
4
|
11.7
|
12
|
18
|
|
Babwata
Eastern Core
|
91
|
91
|
0.5
|
1
|
4.6
|
|
4.6
|
4
|
5
|
|
Kwandu
|
8
|
8
|
0.0
|
1
|
0.4
|
1
|
0.4
|
1
|
3
|
|
Mayuni
|
42
|
42
|
0.2
|
|
2.1
|
1
|
2.1
|
2
|
3
|
|
Mashi
|
18
|
18
|
0.1
|
|
0.9
|
1
|
0.9
|
1
|
2
|
|
Mudumu
|
34
|
17
|
0.1
|
|
0.9
|
|
0.9
|
1
|
1
|
|
Communal
land
|
115
|
58
|
0.3
|
|
2.9
|
1
|
2.9
|
3
|
4
|
|
Mamili NP
|
560
|
280
|
1.4
|
1
|
14.0
|
1
|
14.0
|
14
|
16
|
|
Chobe/Linyanti
|
255
|
128
|
0.6
|
1
|
6.4
|
3
|
6.4
|
6
|
10
|
|
Kasika &
Impalila
|
54
|
27
|
0.1
|
1
|
1.4
|
1
|
1.4
|
1
|
3
|
|
Salambala
|
1
|
1
|
0.0
|
|
0.1
|
1
|
0.1
|
1
|
2
|
|
Communal
land
|
200
|
100
|
0.5
|
|
5.0
|
1
|
5.0
|
4
|
5
|
|
Zambezi
|
17
|
9
|
0.0
|
|
0.5
|
1
|
0.5
|
1
|
2
|
|
Kasika &
Impalila
|
8
|
4
|
0.0
|
|
0.2
|
1
|
0.2
|
1
|
2
|
|
Communal
land
|
9
|
5
|
0.0
|
|
0.3
|
|
0.3
|
|
0
|
|
TOTALS
|
1,387
|
898
|
4.5
|
5
|
44.9
|
10
|
44.9
|
45
|
60
|
Table 7: A notional allocation of hippo quotas in the Caprivi.
The estimates of Stander (2004) are shown in the first column
and these are adjusted in the second column to take into account
the population units 'shared' with neighbouring countries.
Calculations of the sustainable quotas for sport hunting,
problem animal control and harvesting are then made in the
columns labelled 'C'. Sport hunting quotas are calculated
as 0.5% of the Namibian population values, and PAC and harvesting
quotas are based on the maximum sustainable value of 5%.
Illegal hunting
There is unlikely to be any difference between the response
of a hippo population to illegal hunting and legal harvesting
if mortality affects both sexes and all ages equally. This
is likely to be the case if the hunting is for meat or if
the intent of the hunters were to eradicate hippo.
As with harvesting, illegal hunting should have no effect
on the setting of sport hunting quotas because the population
age structure does not change shape from a stable age distribution.
All that alters is the population growth rate. Even when the
level of illegal hunting is unsustainable, a quota of 0.5%
of the total population can be set for sport hunting.
Some illegal killing of hippo is taking place in the Caprivi
both by Namibians and by citizens of neighbouring countries
(Beytell, pers.comm.) but there are few data available to
gauge the extent of it. Although the Namibian legislation
forbids the killing of hippo to protect crops, there are instances
where people take the law into their own hands and deal with
hippo that threaten their livelihoods. In a recent case, notwithstanding
the provisions of the legislation, a court in the Caprivi
found in favour of the defendant - a precedent which throws
into question the workability of the law.
Within the Caprivi, illegal hunting may be reduced by placing
a greater value on
hippos and devolving
more authority to communities. Reducing illegal hunting
by citizens of neighbouring countries is more difficult since
the hunters do not have to enter Namibia to obtain hippo from
the 'shared' population. This problem can only be tackled
by transboundary cooperation.
|
