The pirarucu (Arapaima gigas) is an important fishing resource in the Amazon which has been exploited since the XIXth century. There are indications of a decrease in population size in some parts of its distribution. Management is one of the strategies adopted to maintain fishing activity associated to the conservation of the species. We evaluate aspects of pirarucu populations in two places in the Mamirauá Reserve (Jarauá and Maraã), and
compare these populations with those of Santarém and Tucuruí, analyzing their genetic variability and structure. In order to achieve this, seven microsatellite loci were genotyped for 463 pirarucus from Mamirauá Reserve collected along five years. Our results show a greater genetic diversity for this population in
comparison to populations from Santarém and Tucuruí. Analyses indicate that
management has been ecologically efficient, since there were no significant
change in genetic diversity over the five years of study. Lateral migration,
associated with a possible standardized return to lakes without spacial fidelity
seems to have great importance for local genetic admixture. However, this
admixture is limited in space, with a small degree of genetic differentiation seem
between pirarucus from Jarauá and Maraã. When including more distant
localities to the analysis, the differentiation is greater though geographic distance cannot explain all of this. We believe that a population decline in intermediate localities, probably caused by overexploiting is influencing the connectivity among the localities studied.
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