Environmental Engineering Reference
In-Depth Information
Fig. 7.18 (a) Annual
counts of hunters in
forest reserves in Ghana
are inversely related to
supply of fi sh to the
region. Each data point
represents one year, and
there are 30 years of
data. (b) Year-to-year
change (expressed as λ,
the fundamental net per
capita rate of increase -
see Box 5.1) in biomass
of large mammals in
the reserves. When λ =
1, biomass has not
changed; values greater
than 1 represent an
increase in biomass and
values less than 1
represent a decrease.
Years with a lower than
average supply of fi sh
had higher than average
declines in mammal
biomass, and vice versa.
(After Brashares et al.,
2004.)
(a)
180
160
140
120
100
80
60
40
15
20
25
30
35
40
Per capita fish supply (kg yr -1 )
(b)
1.04
1.00
0.96
0.92
0.88
15
20
25
30
35
40
Per capita fish supply (kg yr -1 )
bushmeat provides a vital food resource to local people, especially when their supply
of protein from a completely different harvest - fi sh from the sea - is short. In Ghana,
for example, the annual consumption of bushmeat is estimated to be at least 385,000
tonnes, compared to 490,000 tonnes of fi sh. Both harvests are at great risk of over-
exploitation, but the problem is compounded because it turns out that the harvests
are inextricably linked (Figure 7.18). Brashares et al. (2004) have shown how bush-
meat hunting increases in wildlife reserves across Ghana during periods of low
national fi sh production, accelerating the declines in wildlife abundance during
these periods. When few fi sh are available to eat, the price of fi sh and the amount
of bushmeat sold in rural markets both rise. It seems clear that people treat bush-
meat as a substitute for fi sh. Determining economically optimum yields in such
a situation is fraught with diffi culty because of the linkage in the markets -
coordinated management is called for. Brashares' team suggests two urgent steps.
First, access to the fi shery of large and technologically advanced foreign fi shing
fl eets should be limited. Second, and given the parlous state of both harvests,
regional livestock and agriculture needs to be developed suffi ciently to take pressure
off the overexploited wild resources.
7. 6 . 2 Confronting
political realities
The ecological and economic models of sustainable fi sheries are, of course,
never perfect. But even if they were, we could still not be confi dent that ecological
 
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