Ecology

HABITAT:

Giant Otters inhabit lakes and rivers in remote areas of the Amazon where there is little human activity. The favoured habitat is oxbow lakes due to their low water flow, high density of fish and small seasonal variation in water levels. Larger lakes are the main breeding habitat and are often responsible for the best reproductive success; rivers are also used but breeding success in rivers seems to be lower. Groups of Giant Otters will often use more than one lake as well as nearby streams, rivers and even palm swamps. Only the largest lakes are able to support a family of otters year round.

BEHAVIOUR:

Giant otters are entirely diurnal (active by day) and highly social. They spend much of the day fishing in open water interspersed with rest periods on logs, banks or in the den. Before dusk the entire family retires to the den for the night. Dens are situated on the higher banks of lakes and rivers and are dug by the otters or taken over and modified from other animals. Dens may have one or more openings which lead to oval shaped chambers. Fallen logs at lake edges and shore areas are often habitually used as latrines or areas for resting and grooming. Being highly social, the members of a group communicate using a variety of sounds including whistles, grunts, clicking sounds and snorts. The unique throat markings of each individual help them identify each other. One notable behaviour of giant otters that you may observe is periscoping, where the otters raise their heads and necks out of the water. Often accompanied by snorting sounds, this behaviour shows that the otters are alarmed and stressed and means that you are too close to them.

DIET:

Giant otters are piscivorous (fish eaters), consuming between 3-4 kg of fish per otter per day. They mostly eat fish between 10-30 cm in length favouring species such as: boca chico prochilodus caudifasciatus, bujurki satanoperca jurupari and huasaco hoplias malabaricus. Normally they do not share their prey but will do so with cubs or if they catch a particularly large fish. Cubs beg from adults in a noisy manner.

POPULATION STRUCTURE:

The population is mainly comprised of family groups that are based around a monogamous breeding pair that retain a territory. This pair is accompanied by offspring from previous years and generally form groups of 3-10 individuals. Young adults in occupied territories, particularly males, may separate from their resident groups and become solitary dispersers, which wander looking for a vacant territory or a group to join. These dispersers sometimes join with others to form transient groups.

BREEDING:

Breeding occurs in the dry season (April to September in Madre de Dios) and each group generally has one litter of cubs per year. Gestation takes 64 to 72 days and 1 to 6 cubs may be born but usually it is 2-4; the female only has 4 nipples so it is rare for more than 4 to survive. Cubs are born blind and remain in the den for 3-4 weeks. At 2 months the cubs start begging noisily for fish and at 4 months are travelling with the group and starting to hunt even though they still take milk until 5 months of age. Hunting success for cubs is very limited until they reach about 10 months of age and they are dependent on other group members for food.

MORTALITY FACTORS:

We know little about natural Giant Otter mortality as dead otters are very seldom found. Mortality of young adults seems to be low but mortality of pups and dispersers appears to be much higher. Diseases such as canine distemper and parvovirosis can be fatal to Giant Otters. They have few natural predators when in the water other than the Black Caiman; even large caimans will not regularly challenge a group of Giant Otters. Other possible predators could include Anacondas, Jaguars and Pumas whilst electric eels and rays could represent a danger to small vulnerable cubs. Without a doubt the main predator has been and continues to be humans, who continue to kill them despite legal protection.