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Commercial hunting was determinant in the disappearance of giant river otters along areas of historical occurrence in the Brazilian Amazonia. After approximately 30 years of absence, giant otters were spotted in the Amanã Lake in 2000, after the creation of the Amanã Reserve. Four years of field surveys were carried out to confirm the presence of giant river otters in the area and to assess local threats to the species. Information on the human impact on this otter population was compiled based on 83 interviews with residents. Areas of overlap used by both otters and humans resulted in negative interactions. The identified threats included: perception of otters as competitors for subsistence fisheries; conversion of natural areas into annual crops; removal of cubs to be raised as pets; and potential disease transmission from domestic animals. Mitigation and monitoring of these threats are paramount for the maintenance of giant river otters in the area.

Cryptosporidium and Giardia are protozoans that can infect humans and wild and domestic animals. Due to the growing importance of diseases caused by protozoan parasites in aquatic species, we aimed to evaluate the frequency of infection by Cryptosporidium spp. and Giardia sp. in aquatic and marine mammals in the northern and northeastern regions of Brazil. We collected 553 fecal samples from 15 species of wild-ranging and captive aquatic mammals in northern and northeastern Brazil. All samples were analyzed by the Kinyoun technique for identification of Cryptosporidium spp. oocysts. Giardia sp. cysts were identified by means of the centrifugal-flotation technique in zinc sulfate solution. Subsequently, all samples were submitted for direct immunofluorescence testing. The overall frequency of infection was 15.55% (86/553) for Cryptosporidium spp. and 9.04% (50/553) for Giardia sp. The presence of Cryptosporidium spp. was detected in samples from 5 species: neotropical river otter Lontra longicaudis (15.28%), giant otter Pteronura brasiliensis (41.66%), Guiana dolphin Sotalia guianensis (9.67%), Amazonian manatee Trichechus inunguis (16.03%), and Antillean manatee T. manatus (13.79%). Giardia sp. was identified in L. longicaudis (9.23%), P. brasiliensis (29.16%), pygmy sperm whale Kogia breviceps (100%), dwarf sperm whale K. sima (25%), S. guianensis (9.67%), T. inunguis (3.81%), and T. manatus (10.34%). This is the first report of Cryptosporidium spp. in L. longicaudis, P. brasiliensis, and S. guianensis, while the occurrence of Giardia sp., in addition to the 2 otter species, was also identified in manatees, thus extending the number of hosts susceptible to these parasitic agents.

After decades of banning commercial hunting, the population of the endangered giant river otter in South America is no larger than 5000 animals, with slightly increasing populations, and apparent reoccupation of parts of its historical distribution. In Brazil, which may hold the largest populations, the refinement of distributional data and the conduction of censuses in Amazonia were identified as essential for the conservation of the species. To confirm if the species was, in fact, reoccupying its historical area, we present here data collected between October 2004 and September 2008 in Amanã Reserve, Central Amazonia. A total of 18,181 km along 13 water bodies were surveyed in 465 days of fieldwork, resulting in 711 records. Animals presented a uniform occupation pattern, with expansion to new areas, no vacancy of previously used ones, and with frequent reuse of sites along the years. However, considering the number of records/km and sightings/km were almost constant between years, the local population may be experiencing just a slight increase, with animals probably expanding their home ranges. Although our study witnessed some population growth, giant river otters remained at low numbers during the survey, indicating that such population still have not reached its carrying capacity and require continuous attention.