Fisheries in the Southern Border Zone of Takamanda - Impact ...

132 Sunderland-Groves et al.
proved unnecessary. All evidence of human activity
(traps, snares, hunter paths, bush houses, spent cartridges,
gunshots heard, etc.) was recorded to evaluate hunting
pressures. We also recorded changes in topography and
vegetation along each transect. The sampling effort
between transects was standardized by keeping the
number of observers, speed of travel, and time of day
consistent. Transects were not walked during heavy or
medium rainfall as this affects mammal movements and
observer reliability (see Sunderland-Groves and Maisels
this volume).
For ape nests, care was taken to distinguish “definite
gorilla nest” (nest on the ground or tree nest with gorilla
dung underneath) from “definite chimp nest” (tree nests
with chimp dung underneath). If a nest site had both tree
and ground nests, it was a definite gorilla nest site
because chimps never build ground nests. Ape dung is
easily distinguished by smell and form, but old tree nests
without dung cannot be assigned to gorillas or chimps
with confidence. Therefore, nest sites where all nests
were in trees were recorded as “tree-only nest sites.”
Upon locating a nest site each area was thoroughly
searched to ensure that all nests within the group were
identified and recorded. These data were then used to
calculate mean nest group size.
Random nest searches were conducted in highland
areas either after data collection on transects had been
completed or to confirm presence or absence of apes at
sites where time was not sufficient to conduct transect
surveys. The additional data recorded during nest
searches were used to calculate overall mean group size.
Nest data collection during random nest searches
followed the same protocols as those undertaken during
transect surveys.
4.4 Data analysis
4.4.1 Distribution of apes and of human
pressure
Distribution of gorillas and chimps within the
Takamanda Reserve and adjoining forests was inferred
from the geographic location of sign that could be
definitely assigned to one of the two species.
Takamanda: the Biodiversity of an African Rainforest
4.4.2 Group size
Each nest site is the sleeping site for one group of apes
for one night. All weaned individuals make one nest per
night, so the size of each nest group is an indicator of
group size. There are variations as occasionally apes may
make a second nest during the night or sleep on the
ground without making a nest. However, mean group
size can be roughly calculated for gorillas using all nest
groups that can definitely be assigned to gorillas. Mean
nest group size and standard deviation for nest groups
that could only be assigned to “apes” were calculated
from the tree-only nest sites.
4.4.3 Abundance of apes and of human sign
The encounter rate (number of observations per km of
transect) was used to estimate relative abundance of
humans and apes throughout the survey and also to
compare between sites and seasons.
Because DISTANCE could not be used, gorilla and
chimpanzee densities were roughly calculated under the
formula proposed by Tutin and Fernandez (1984):
[(N/A)/V][M]=D,
where N=number of sleeping sites, A=area sampled
in km 2, V=mean number of days the nest remains visible,
M=median nest group size, and D=number of weaned
individuals/km².
Encounter rates were calculated (number of nests or
nest sites per km walked, per stratum, and/or per season)
and compared between strata and seasons between this
study and previous work by March (1957) in the same
region, and gorilla surveys carried out elsewhere in
Africa (Williamson and Usongo 1995, Maisels and
Cruickshank 1996, Hall et al. 1998).
In the lowland forest at Lopé, Gabon, gorilla nests
remained visible for an average of 78 days (Tutin et al.
1995). Mean chimp nest duration in Gabon was 113.6
days (Tutin and Fernandez 1984). Since no data are
available on the deterioration rate of nest sites in