Top of the food chain predators are often not predated upon. However, even though the giant otter (Pteronura brasiliensis) is in that category, the literature mentions many species as potential predators, including the jaguar (Panthera onca). Notwithstanding up until now there has been no registered confirmation of jaguar predation on giant otters. A predation of a jaguar on an adult female giant otter was recorded for the first time during our radio-telemetry study on giant otters in Balbina hydroelectric reservoir in Central Brazilian Amazon. The female had had a transmitter implanted on February 2012 and was killed by a jaguar ninety-four days after the surgery. This giant otter was a solitary specimen, which was captured by a jaguar while asleep in a shelter under a fallen tree trunk on the banks of one of the reservoir’s islands. The solitary pattern found in such individuals combined with the frequent use of shelters, allows predators to access them more easily and may have contributed to the predation observed in this study.

According to the literature, giant otters produce one to six cubs at each gestation, with birth peaks occurring from the end of the flood season to the beginning of the low-water period. With the aim of describing some reproductive parameters of the giant otters living in a hydroelectric lake, 56 field excursions to Balbina Hydroelectric Reservoir, hereafter Balbina Lake, were carried out between September 2001 and September 2010 in order to gather information about cub weight and length, litter size and reproductive period of the species in that area. About 80% of the birth records occurred between September and December, characterized by the receding water season and the beginning of the dry season. The number of cubs per gestation varied from one to three animals (mean = 2; n = 36) and average weight and length of neonates were 316.25 ± 64.21g (n = 4) and 31.75 ± 4.86cm (n = 4), respectively. The reproductive period and the litter size produced by giant otters in Balbina Lake were within the range reported in literature for non-dammed areas, indicating that these reproductive parameters were not changed by the reservoir. The weight of cubs analyzed in the reservoir was in average 35% greater than the weight of captive newborn cubs reported in the literature. However, as the animals here analyzed were healthy, it is reasonable to assume that they represent the weight of free-ranging newborn cubs. Artificial lakes had been reported in the literature as favorable environments for giant otters in Guyana, and the results obtained here seem to corroborate this hypothesis and show the plasticity of the species in its use of different habitats as long as the habitats are inside some category of protection, in this way minimizing additional impacts caused by an intense human occupation of the area. Resumo:De acordo com a literatura, as ariranhas geram de um a seis filhotes a cada gestação, com pico de nascimento das crias entre o final da cheia e início do nível baixo das águas dos rios. Com o objetivo de conhecer alguns parâmetros reprodutivos da ariranha em lagos de hidrelétrica, foram realizadas 56 expedições ao lago de Balbina entre setembro 2001 e setembro 2010 e registradas informações sobre o peso e comprimento de filhotes, tamanho da prole e período reprodutivo da espécie no reservatório da Usina Hidrelétrica de Balbina. Cerca de 80% dos registros de nascimentos ocorreu entre os meses de setembro e dezembro, que correspondem às estações de vazante e início da seca na área de estudo. O número de filhotes por gestação variou de um a três animais (média = 2; n = 36) e o peso e comprimento médios de neonatos foram de 316,25 ± 64,21g (n = 4) e 31,75 ± 4,86cm (n = 4), respectivamente. A semelhança quanto ao período reprodutivo e número de filhotes gerados pelas ariranhas de Balbina quando comparados com áreas não represadas revela que, apesar dos distúrbios ambientais causados pelo represamento, estes aspectos reprodutivos da espécie não foram alterados. O peso dos filhotes analisados no reservatório foi e...

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