Geoscience Reference
In-Depth Information
300
250
200
150
100
50
0
10
0
10
2
10
4
10
6
10
8
Abundance (Number individuals 10
5
m
3
)
Figure 3
Diets and prey species abundance: y-axis represents the number of indivi-
duals sampled for each species as a function of the estimated local species abundance
for all the environmental conditions (R
2
ΒΌ
0.46, [0.28-0.61, 95% confidence interval],
p
<
0.01).
Drake et al., 2002
). Estimations of abundance were collected in each of the
three stations with a total of 144 samplings (12 months
4
samplings). At each new moon, four samplings were collected in each station
during a period of 24 h and synchronized with tides (two starting at 'low
tides' and two starting at 'high tides').
All samples were caught from a traditional fishing boat anchored on
the left river side. Samples consisted of passive hauls, lasting 2 h, made
during the first 2 h of each diurnal and nocturnal flood and ebb tide.
Samplings were taken with three nets working in parallel. Nets were made
with polyamide gauze from a mesh of 1 mm and an opening of 2.5 m (width)
and 3 m (depth).
The total catch from each sampling was discharged into a calibrated
container and its volume estimated. Thirteen litres of the collected material,
or the total volume when the catch was smaller, were randomly sampled
using a calibrated (1 l) beaker and preserved in 10% formaldehyde. In the
laboratory, individuals were sorted into species, counted and analysed. At
the start of each sampling, water temperature, salinity and turbidity were
measured. During sampling, the current speed was measured with a digital
flow metre placed near the nets, so abundance of the different species are
given per 10
5
m
3
of filtered water.
3 stations
