Environmental Engineering Reference
In-Depth Information
effort stayed constant, you would expect to see an increase in poaching signs (such as
arrests or discovery of snares or damaged trees). However, because increased enforce-
ment effort is not just passive monitoring but also leads to deterrence of poaching,
you would expect to see low evidence of poaching activity at both high and
low monitoring efforts, and high evidence of poaching activity at medium effort.
Therefore, if there is no sign of poaching activity this can be because there is no
effective monitoring, or because there is no poaching. It's not always obvious which
of these pertains without independent information, because if monitors are not
going out at the right times to the right places, it may appear that poaching has
ceased.
In order to analyse monitoring data, it needs to be corrected for
observer
effort
—for example, by creating an index of the number of poaching signs
encountered per observer day. Over time, with consistent law enforcement effort
which has the same probability of detecting any single poaching incident in each
time period (i.e. there is no change in observer effort or in poacher avoidance
behaviour), then a decrease in the number of poaching signs observed is good evi-
dence that poaching has indeed declined. By dividing the number of signs by
observer effort, we can look at changes in poaching activity over time even when
the amount of effort put in is variable. But it is harder to correct for changes in the
type of monitoring carried out and in poacher avoidance behaviour.
Box 7.2
Ranger-based monitoring for mountain gorilla conservation.
In the Virunga and Bwindi forest areas, the International Gorilla Conservation
Programme has been involved in a ranger-based monitoring programme since
1997. Rangers collect data on locations of gorilla groups and poaching signs, and
these data are visualised in maps and graphs of trends over time. The data collec-
tion has been useful in highlighting periods when incursions into the park to
snare bushmeat or collect bamboo or water are particularly common; this tends
to be in the dry season, June to August. Because the gorillas are habituated and
tourist groups are taken in to see them, the data on gorilla locations has a prac-
tical use in guiding tourist visits and pinpointing areas of potential human-gorilla
interaction, rather than being used to monitor trends in gorilla population sizes.
Instead, periodic scientific censuses are used to give robust estimates of trends in
population sizes. A comparison of information from household surveys (asking
whether they collect water inside the park) and data on incursions from the
patrols shows a strong spatial correlation, suggesting that the rangers are obtaining
useful and verifiable information (Figure 7.2). A comparison of the location of
human incursions and gorilla home ranges can be used to show the key areas
of overlap and also areas where human presence may be excluding gorillas from
otherwise suitable habitat.
