Critter of The Week #19: Giant River Otter


The giant river otter is the longest of all otters and the largest member of the weasel family, which includes other animals like mink, ferrets, skunks, and the wolverine. They can reach lengths up to 6 feet long and weigh 75 pounds! 100 years ago, some large males were even recorded to reach lengths of up to 7 or even 8 feet. Such large specimens are almost unheard of today. 


To giant otters, family is everything. They are the most social of all otter species and live in extended family groups centered around a breeding pair. It would be like you living with your mom and dad and many older brothers and sisters. They are very closely bonded and will eat, sleep, travel together, and fiercely defend each other during dangerous encounters.


Giant otters live in rivers and lakes in the Amazon basin and are perfectly equipped for an aquatic lifestyle with webbed feet, a long powerful tail, and a long streamlined body.


Giant otters are the most vocal of all otters too. Researchers recorded as many as 22 different vocalizations in adults and around 11 in juveniles. Their loud and almost comical voices help them stick together and keep track of each other during their daily escapades in the thick forest.


Giant otters are very curious and inquisitive. They will regularly swim up to boats to investigate visitors. The reason for this is because they are apex predators with no natural enemies except humans. Their family groups and large size makes them formidable opponents to other large predators like caiman and even jaguars.

Scientific Classification

Kingdom : Animalia

Phylum : Chordata

Class : Mammalia

Order : Carnivora

Family : Mustelidae

Genus : Pteronura

Species : Pteronura brasiliensis


Conservation Status 

The International Union for the Conservation of Nature classifies the giant otter as endangered. Their population is at risk of declining if further protections are not instituted. They are currently threatened by hunting, logging, and unsustainable agriculture.


Physical Description 

Giant otters are large and well-adapted for an aquatic life like most of their cousins. They have large webbed feet, a long and powerful tail, and a tubular streamlined body making them the acrobats of the rivers.


They can grow up to 6 feet long and weigh up to 75 pounds, making them significantly larger than most other freshwater otters. The males are usually slightly larger than the females. 


Their coat is a dark brown color with creamy white markings on their chest. They use these markings to help identify each other almost like a fingerprint and will display their chest out of the water when they meet, almost like a calling card so they know who is who. Their coat is extremely short but dense and velvety. It is so dense, in fact, that water does not reach their skin!


They also have ears and nostrils that close up when they submerge themselves much like a hippopotamus. Like all otters, they have a short, stubby face and are carnivores with a very powerful bite. The sagittal crest on their skull is where large powerful jaw muscles are attached.




Giant otters are apex carnivores and prey mainly on fish. Scientists discovered that 97% of their diet is fish. This even includes piranha. If fish are not around, they will eat small snakes including young anacondas, turtles, frogs, and even small caiman.


Although they will eat together and hunt together, they rarely cooperate like lions to bring down a single prey item. It is more akin to them all chasing down their own fish and eating it all together. It is only when the prey is larger or is threatening do they band together to bring it down.


When they eat, they grasp food with their front paws and will eat it head first. Young otters learn this important skill early on especially when your food can bite back like the piranha!


Believe it or not, giant otters have to eat anywhere from five to nine pounds of food everyday to maintain their body weight and energy levels. Imagine how much weight you would gain if you ate that much!


They are diurnal, which means they hunt by day and sleep at night. When they do hunt, they rely primarily on eyesight and will stick to areas where they can spot fish in relatively shallow water; usually about two feet deep on average. Scientists also notice they stick to slower and more clumsy fish species and catfish as their main prey. 


When they are chasing fish underwater, their extremely sensitive whiskers help them sense pressure fluctuations in the water so they can chase down fish.


Here you can watch a short clip from the BBC that shows how the giant otters hunt, and the incredible array of vocalizations thy have.



Behavior and Intelligence

Giant otters have large brain-to-body ratios as can be seen by their skull. They are the most socially and vocally complex of all the weasel family and all otters. Because they are so social, this also makes the need for more complex brains.


Originally, scientists believed giant otters had only a few general calls for things like danger, reassurance, and play. Yet recent studies discovered the list stretches as long as 22 different vocalizations for adult otters and around 11 for pups.


Young otters will engage in babbling sounds much like human infants, which helps them develop more complicated communication as they grow.


Giant otters are also territorial and will identify their territory with vocalizations, latrines or areas that are like communal bathrooms, and scent markings. 


Giant otter families center around a monogamous breeding pair, or mom and dad. Groups are usually comprised of two to over a dozen members and are usually siblings from previous years.


They are incredibly brave as a group and even a Jaguar doesn't phase the family unit!


Reproduction & Life Span

Giant otters breed all year-round but most pups are born in the dry season when the water levels in the lakes and rivers are lower and the fish population is at its most dense. They give birth on land and will dig dens in sandy riverbanks usually around tree roots.




When it comes time to mate, the males usually make the advances and will copulate in the water.


Their gestation period is around 70 days and the mother will give birth to two blind, helpless pups that are raised in the den. Both the male and female will help rear the pups during their most vulnerable period in the first week or two. But as the pups grow, the older their brothers and sisters will pitch in and everyone brings them fish, protects them, and plays with them.


They are very protective of their young and will defend them fiercely from predators, as can be seen in this harrowing video of a giant otter family successfully defeating a large caiman they saw as a threat.



The pups will open their eyes in about one month, are able to walk around a week later, and can swim confidently in three months.


The juveniles will stay with the family for about two years and then venture out on their own and start their own family.



Distribution & Habitat

Giant otters live in rivers and lakes in several areas throughout the Amazon basin. 


They prefer a variety of different habitats but will go to any rivers with an abundance of food and proper denning areas.


They prefer seasonally flooded marsh forests, and rivers and streams with clear water and rocky bottoms vs. silty  or sandy bottoms.


Giant otters will clear large amounts of vegetation along river banks for campsites, communal latrines and dens for pups. These areas can include tunnels that have many entrances and exits.


Giant otters have been driven from 80% of their original range, but they currently still live in Bolivia, Brazil, Colombia, Ecuador, Paraguay, Peru, Guyana, French Guiana, Suriname, and Venezuela. Some scientists agree the best otter habitat is in French Guiana and Guyana and represents the brightest future for the species.



The estimated remaining population of the giant otter is anywhere from 1,000 - 5,000 individuals. This makes them the rarest otter species in the world. The largest population may be in Brazil's extensive wetlands in the Pantanal. Estimates range as high as 1,000 giant otters in the region, but may be lower. 


Relationship with People

Despite their curious and playful nature, giant otters have a mixed relationship with the local humans. Before European colonization, they were viewed by most native tribes as competitors and pests and were hunted and killed. 


When Europeans arrived, and as South America was developed, they were extensively hunted for their pelts driving them to near extinction in the 1950s and 1960s. 


Protections were finally put in place and they partially rebounded. Yet today, they still face a variety of threats from people.


There is still poaching for their pelt and logging for rare mahogany trees that destroys forest near riverbanks. The farmers come in after the loggers and their practices erode the soil and deplete nutrients, forcing the otters to relocate.


They are also persecuted by fisherman and face poisoning from pollution from gold mining in the region.


The good news is as of 2004, Peru created one of the largest conservation areas in the world, Alto Purus National Park, which includes giant otters and giant otter habitat.


You can do a few simple things to help giant otters. First, pass up any opportunity to buy wildlife products such as fur coats or fur products of any type. Demand for any of these products and any wildlife derived product leads to demand for ever more rare and unique animals, and inevitably drives poaching of species like the giant otter.


Also, when buying furniture, avoid any type of mahogany or rosewood.


And if you ever visit any countries in the Amazon basin, stop by any of the national parks in the region and see some otters for yourself. Ecotourism puts some stress on the otters, but as long as you keep a safe distance, minimize noise, and use reputable operators to view otters, you can enjoy them while they live naturally. 


CritterFacts CritterKnowledge Ranking


We rank each new Critter of the Week based on how much information and resources we find online about each animal. We rank on a scale of 1-10. 1 being very little information available or only very basic information available and there is a need for more research. An example would be a newly discovered deep sea creature like the blobfish. A ranking of 10 means there is abundant and easily accessible information available on all aspects of a species. An example would be chimpanzees. We will use this gauge to help us guide future research efforts to learn more about new animals we include in our Critters of the Week!