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hundreds of kilometers, according to the climatic period. For
S. guianensis
, the food
availability and depth are important variables for the habitat permanence and use. But it is the
depth in addition to dolphins that can restrict the distribution of some fish species.
Table 6. Statistics of the interactions among variables analyzed for
Sotalia guianensis
in
the Amazon Estuary from 1999 to 2001 (A = Area; H = habitat characteristics where the
species are found; GS = Group size; OD = degree of species occurrence, B = Behavior; C
= frequency of calf observation; df = Degrees of freedom; G = Corrected value of the
test; P = Probability). The significant probabilities are in bold.
Interaction
df
G
P
Interaction
df
G
P
1. H*GS*OD
24
12.1
0.98
2. H*GS*B
12
9.36
0.67
H*GS to GO
36
151.7
3.3x10
-16
H*GS to B
24
163.94
0
3.5x10
-8
H*OD to GS
30
44.9
0.03
H*B to GS
15
64.9
GS*OD to H
32
29.05
0.61
GS*B to H
16
31.03
0.01
3. H*GS*C
24
13.2
0.96
4. A*H*C
48
46.9
0.51
1.1 x10
-12
5.8x10
-13
H*GS to C
36
130.9
A*H to C
72
192.7
H*C to GS
30
31.7
0.38
A*C to H
64
82.4
0.06
GS*C to H
32
70.3
0.0001
H*C to A
54
86.9
0.003
5. A*GS*B
32
30,6
0.53
6. H*OD*B
6
1.3
0.97
A*GS to B
64
109.5
0.0003
H*OD to B
12
25.6
0.01
5.2x10
-5
A*B to GS
40
46.4
0.22
H*B to OD
9
35.3
GS*B to A
36
49.5
0.06
OD*B to H
8
16.4
0.03
7. H*C*B
6
10.4
0.10
H*C to B
12
26.1
0.010
H*B to C
9
24.2
0.004
1.3x10
-6
C*B to H
8
49.1
All the areas identified by the interviewees as places where species occurred were
considered common. Only areas such as Belém, Salinas and Soure presented seasonal
occurrence similar to the common one. Those were port areas, with high vessel traffic, as well
as with leisure beaches. These characteristics in association with the tide system make the
dolphins explore them more frequently in the high tide periods. It is also possible that
S.
guianensis
in the Amazonian estuary avoids areas with heavy human intervention; different
from other points of its geographical distribution.
Several authors indicated that lagoons, bays and estuaries as preferable habitat for this
species, and to a lesser degree, the open sea (Borobia et al., 1991; Silva & Best, 1996; Carr &
Bonde, 2000). While within the Amazonian estuary,
S. guianensis
will move among these
habitats changing locations as they change activities. Thus, they were observed at beaches of
exposed coast, as well as in igarapés, smaller estuaries and bays or mangrove lagoons.
Apparently, differences in habits of this species are linked to the tide effect and the depth and
distribution of its prey; relationships that have already been recognized for this species
(Edwards & Schnell, 2001).
Estuaries are important areas for
S. guianensis
feeding where coast topography, water
temperature, salinity and depth are decisive environmental variables for their prey distribution
and abundance. According to Barthem (1985) the Amazonian estuary fishing stock
distribution and abundance vary according to the depth and salinity.
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