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agree with our genetics results in the sense that the fidelity for lagoons seems to be important
for a significant fraction of pink river dolphins. In fact, the negative correlation between the
monthly proportion of marked pink river dolphins in the Mamirauá lake system and on the
river within two kilometers could indicate that many resident animals traveled small distances
when forced to go to the river during the low water season. On the other hand, Martin & Da
Siva (2004a) detected individuals which moved from tens to hundreds (even up to 1000) of
kilometers along the rivers, but without broad-scale seasonal migration. It is possible that
some animals travel many kilometers along the rivers, but this individual movement does not
mean ―gene movement‖, because these exemplars can return to their original lagoons to
breed. In fact, although a substantial amount of movement in the Mamirauá area was
demonstrated on any particular day when a large fraction of the marked resident animals were
outside of the lake system, almost all of them returned after periods of days, weeks or even
years. Moreover, these authors only found a low percentage of marked animals on rivers
outside the influence area of Mamirauá (1.3 %), which agrees quite well with a strong
phylopatry for this species for both sexes. For instance, I detected that 12 % of the
individuals (4/33) had genetic profiles which more probably belonged to other lagoons from
where they were captured. If I analyze in detail the sex of these animals the picture was as
follows: The two animals in lagoon 4 with more genetic resemblance to individuals from
lagoons 6 and 7 were adult females as well as the animal of lagoon 7, which grouped with the
animals of lagoon 8. Contrarily, the individual from the lagoon 6, which was classified
together with the individuals from lagoon 7, was an adult male. Furthermore, in all the cases,
these possible migrants, or descendents of migrants, were coming from other lagoons in the
upper basin of the river. It seems that these animals descended the river to integrate
themselves into other lagoons. Nevertheless, we cannot know if these animals were migrants
(or migrant descendents), which were reproductively integrated in the new lagoons, or were
simply occasional visitors. Thus, I cannot emphatically decide if the very low gene flow
found among the lagoons were caused by males or females (d
m
or d
f
= 0.22), but the
Chesser´s simulations demonstrated that it cannot be a simultaneous contribution of both
sexes. If the exemplars, with different genetic profiles in regards to the lagoons where they
were sampled, were reproductively integrated into these lagoons, then, it seems more
probably that females are better contributors for gene flow. Data from Martin & da Silva
(2004a) agree quite well with this possibility. They found that the proportion of residents that
were males (52 %) was higher than that of non residents (43 %), although this difference was
not statistically significant. Additionally, the data of these authors showed that it is probable
that males presented a similar degree of site fidelity to the lagoons as females, although they
simply spent less time in the lagoons and more on the rivers near the lagoons. However, I
detected that females and their calves used lagoons preferentially, such as Martin & da Silva
(2004b) determined in Mamirauá, and where males were numerically dominant in the main
rivers. Therefore, the probability to catch females was higher than for males. This could also
explain why three of the four animals, with genetic profiles that did not belong to the lagoons
where they were sampled, were females. If the males spend more time in the main river
channel, they have a greater possibility of traveling to distant lagoons compared to females.
Moreover, adult males are more robust and strong than females and this could enhance the
possibility for swimming greater distances along rivers. If this is true, then, males could be
the decisive sex that carries out gene flow among the different lagoons. But, philopatry is
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