Giant Otter Facts

Scientific name: Pteronura brasiliensis ("Brazilian wing-tail", which refers to their flat, airfoil-like tail).

Local names: Lobo de rio, ariranha, waterdog, lontra, nutria, lobos

Taxonomic group and close relatives: The Giant Otter is the longest and most powerful of the world´s otter species, but ties the Sea Otter of the North Pacific as the heaviest of otters. Otters are in the carnivore order of Mustelidae, which also include badgers, weasels, mink, martens, fishers, wolverines, and other notoriously ornery carnivores. The Giant Otter and European is the only group-living mustelid, and this group living makes them especially interesting, complicated, and fun to observe.

Length: 1.7-2.0 m.

Weight: 26-32 kilos

Diet: Each adult otter eats 6-10 kilos per day of fish of all sizes, though typically in the size range of medium-sized piranhas up to 3-kilo fish of many species. These voracious otters also eat any other vertebrate that is not fast enough to get away from them. Our team in Peru and other researchers have seen Giant Otters eat 20-kilo catfish, anacondas, other snakes, caimans, and occasionally even careless herons. When they ate anacondas, they looked like a gang of acquatic "Taz"´s *(the Warner Brothers cartoon character) trying to subdue an out-of-control fire hose.
Group size: 2-12, with healthy groups in good habitat typically reaching 6-12 animals.
Breeding system: One reproductive pair of adults, accompanied by juveniles and young adult offspring. Young stay in group for 2-5 years or more and help babysit new cubs, which is to say, protecting them from attacks by lurking caimans and other predators. The members of a group normally do not share fish, but rather each catches and eats its own. The breeding female and male, however, will capture and maul fish and then cede them dead or half-dead to their cubs.

Territoriality: Giant Otter families are extremely territorial, and in the low water season in particular stake out highly defined linear territories along narrow rivers in the Pantanal and the Guyanas. In 2003-2004 in the SW Pantanal, Brazilian researchers Carolina Ribas and Guilherme Mourão, who are at the Brazilian research institute EMBRAPA, in Corumbá, mapped six groups that had non-overlapping, sharply-defined, exclusive territories. These territories occupied every single metre of a 30-km-long stretch of the 200-m-wide Miranda River and its 40-m-wide tributary, the Vermelho River.Litter size: the single breeding female in the group gives birth annually to 2-4 cubs, normally in the low-water season.

Enemies: Jaguars probably take young and lone otters in semi-flooded forest during the flood season, and large Black Caimans and large Anacondas probably can take a lone otter. Probably the Giant Otter lives in groups not to increase hunting success per animal, but rather to allow them to survive and prosper in slow lakes and rivers full of large Black Caimans and large Anacondas, which otherwise could finish off lone otters one by one. My research team saw a number of extraordinary, bloody fights between large Black Caimans and family groups of Giant Otters. In one fight, a 4-metre-long Black Caiman struck an otter with a mighty blow from its massive tail, hurling the otter clear out of the water and up onto the lakebank. In another fight, a family of otters fought a 3.5-m-long Black Caiman for 45 minutes only 20 m from a boatload of astounded tourists. The otters inflicted serious damage on the caiman, which ended up losing one of its front legs. On another occasion, a family of otters killed and entirely consumed (legs, tail, bones, everything) a 1.5-m-long Black Caiman. It took them 2.5 hours to consume the hapless reptile.