Giant Otters (Pteronura brasiliensis) were on the brink of extinction with an estimate of just 300 individuals left in the wild in the 1980s, according to an IUCN report.
The primary cause for this population decline was poaching for otter pelt. After hunting restrictions, their numbers rebounded but now the limiting factor for the otters is a lack of fish. Everywhere in the Amazon, fish stocks are decreasing due to commercial over-fishing.
A significant population of giant otters lives in the wetlands of the central Araguaia river, and in particular within Cantão State Park, which with its 843 oxbow lakes and extensive flooded forests and marshlands is one of the best habitat patches for this species in Brazil. Currently, the Instituto Araguaia is working in conjunction with the Cantão State Park authorities in order to prevent illegal fishing and poaching in the park. The Instituto also maintains a research station in a pristine area of the park, and patrols the area for fish poachers, whose activities bring them into direct conflict with the otters. Without the former fish poaching, the rivers and lakes in the area are teeming with fish, and we have been observing a triumphant return of the population of giant otters. Not only the sightings are becoming very frequent, but also the otters are becoming increasingly familiar with our peaceful, but constant, presence. This has allowed us to observe and film them for long hours during their routines.
According to our observations, which are based on the methodology established by the IUCN and described in the publication "Surveying and Monitoring Distribution and Population Trends of the Giant Otter, IUCN/SSC Otter Specialist Group", in Cantão State Park otters dig their reproductive dens on the shores of oxbow lakes starting around July, when waters are already quite low. They birth between August and September. The young cubs emerge for the first time in October and November, which are the months of lowest water, when fish concentrations are in the dwindling lakes and channels are at their peak. This makes it easier for the adults to catch enough fish for the growing cubs, and for the cubs themselves to learn how to catch fish. The entire group, including non-reproductive adults which are usually older siblings to that year's cubs, collaborates to catch enough fish for the youngsters.
We hope that this survey will serve as a basis for a permanent population-monitoring program for P. brasiliensis in Cantão State Park.