Geoscience Reference
In-Depth Information
60
MPA
HCR
Fixed
50
40
30
20
10
0
0
20
40
Target Catch
60
80
100
Figure 25.7
Simulation of mean annual catch in a marine fi shery over a 100-year
period, based on different target catches used in three management strategies: fi xed
(where the same catch is taken each year), harvest control (where catches are reduced
if the population falls below a critical threshold) and marine protected areas (where
yields are taken from only half of the population). Based on these models, only the
marine protected areas management strategy would result in sustainable manage-
ment. Taken from Pitchford et al. (2007).
processes provide context and guidance for current management of ecosystems; and
(ii) spatio-temporal variability driven by disturbance is an intrinsic part of ecosys-
tems. It therefore supports non-equilibrium paradigms over short temporal scales.
As a management technique, the use of past, or undisturbed, conditions as reference
templates for management and restoration was suggested by Leopold et al. (1963),
in the form of natural vignettes which imply ecosystem integrity. Since then, greater
appreciation, measurement, and quantifi cation of variability has refi ned the simplis-
tic idea that some natural, non-anthropogenically disturbed ecosystem state can be
used as a benchmark for management. Nevertheless, understanding past ecosystem
dynamics offers a useful way of predicting and reducing current management
impacts, and the principles of natural variability certainly have a place in resource
management.
It is important to acknowledge the chaotic, non-linear, and above all, unpredict-
able nature of ecosystems and their resources, and to avoid management practices
that force ecosystems outside of their range of natural variability. This includes over-
simplifying the system, restricting natural disturbances, or intensifying the frequency,
severity, and duration of disturbances. There is increasing evidence that the prin-
ciples of natural variability are being incorporated into management of some ecosys-
tem resources, although there is still much progress to be made. A priority is to
incorporate variability within biodiversity conservation and restoration, which is a
relatively recent form of ecosystem resource management. The absence of objective
scientifi c reasoning, pre- and post-project monitoring, and hard scientifi c training of
practitioners, has resulted in many attempts at conservation and restoration around
the globe being based on an idealised concept of steady-state ecosystems that have
