Environmental Engineering Reference
In-Depth Information
Fig. 7.4.
Women selling crayfish. Photo © Julia Jones.
that they would be prepared to invest 720 person days per year in monitoring
their resources that could otherwise be spent harvesting or in other economic
activities. Loss of economically active time to monitoring could be avoided by
using actual harvest rates instead of experimentally applied catches, but error in
recording effort would make the results even less precise than the already rather
weak 80% chance of detecting a substantial (30%) decline. These levels of power
are fairly typical for wild populations, which may partly explain why local people
do not indulge in detailed resource monitoring independent of harvesting. The
issue for management in this case is to decide whether the low cost of harvest
monitoring is sufficient reason to use it, despite its low power.
detect trends and costs of implementation). These questions have been asked in
commercial fisheries science, because they involve investment in an economic
resource (e.g. Clark and Kirkwood 1986), but are only just starting to be asked in
conservation.
There are usually several methods available for monitoring ecological trends,
and a number of studies are now appearing that compare them in terms of cost-
effectiveness. Some studies discuss methods that are suitable for professional
conservationists. For example, Joseph
et al
. (2006) look at when simple
presence-absence surveys for birds outperform detailed counts, which give more
information but are substantially more expensive. Gaidet-Drapier
et al
. (2006)
