Giant Otters have to be high on every wildlife watcher’s wish list but the only way to see them in the wild is on a tour to South America. So, before you go, here’s everything you need to know about what makes Giant Otters so special.
Giant Otter Facts
As the largest member of the weasel family (Mustelidae), Giant River Otters can easily reach six feet in length and weigh over 30 kilograms. Unlike other otter species, males and females are similar sizes.
How big is a Giant Otter?
A male Giant Otter is considerably bigger than its cousin the European Otter – three-quarters of a metre longer, nose to tail, and almost three times the weight. Giant Otters can reach 1.7 metres length and weigh over 30 kilograms.
Jaguars, which inhabit the same territory as Giant Otters, are only slightly longer but they are much heavier.
Nevertheless, it is well documented that the sleek and agile otters can more than hold their own in a confrontation with a big cat that has invaded their riverbank. In fact, some local Amazon tribes call the Giant Otter an ‘aquatic jaguar’.
Photo credit: Patrick Beese, Giant Otter size comparison to human
Another illustration of the size of a Giant Otter: taking into account its much longer tail and shorter legs, it is similar in size to the average German Shepherd dog.
Giant Otters have thick, brown fur and a creamy-white pattern on their throats – a mark which is believed to be unique to each individual. Known in Spanish as the river wolf (Lobo Del Río), they are endemic to South America and occupy a variety of habitats such as lakes, swamps and slow-moving rivers throughout the Amazon River basin.
During the rainy season, they also inhabit flooded tropical forests. The species can be found across the continent including Peru, Venezuela, Guyana, Brazil, Colombia and Ecuador, although their populations are not stable and are often sparse.
Giant Otter Diet
Giant Otters are carnivorous and feed mainly on fish, including the flesh-eating species beloved of Hollywood jungle movies, the piranha. However, their diet also includes birds, small mammals, invertebrates, crustaceans and even snakes.
Aside from humans, their main predators are jaguars, black caimans and anacondas, although, due to their large size, Giant Otters can also compete for food with these species.
Photo credit: Rainforest Expeditions
These otters are well adapted for life in aquatic habitats with their paddle-like tails, webbed claws, water-repellent fur and the ability to close their nostrils and ears when swimming.
They have strong eyesight and use their whiskers to detect changes in the water current.
The family group hunts together, but each individual catches its own prey. Once they have hunted successfully, Giant Otters bring their prey to a “picnic area” to eat straight away.
So, as you find with other otter species, keeping an eye out for a flat rock near the water that is covered in fish scales can give a clue to there being Giant Otters about.
Giant Otters behave differently to other mustelids. As well as being incredibly social animals, they are also diurnal – active during the day.
The family group, called a raft, a romp or a bevy, consists of a single monogamous pair and their offspring from previous years. These ‘teenagers’ do not breed but assist the dominant pair with feeding, grooming and ‘babysitting’ instead. This phenomenon is known as alloparenting.
Breeding occurs throughout the year but peaks in late spring and early summer. A litter of one to five cubs is born underground in dens along the riverbank.
The young otters learn to swim at around two months, are weaned at six months but rely on the adults for food for the first year and a half, eventually becoming sexually mature at two or three years old.
In family groups sometimes as large as 15 or even 20 individuals, communication is essential and Giant Otters are particularly noisy animals – another sign to listen out for on a Giant Otter tour.
Nine different vocalisations have been recorded, ranging from barks to screams to whistles that express alarm, interest and, in cubs, a need for attention.
As well as sound signals, Giant Otters leave scent marks as important territory signs, particularly around their latrines.
From the 1940s to 1973 the desire for Giant Otter skins decimated populations in Paraguay, Uruguay and Argentina.
The devastating effects of the pelt trade have meant that Giant Otter populations are taking a long time to recover.
Photo credit: InkaNatura Travel
With only small litters, a high mortality rate among cubs and a late age of sexual maturity, Giant Otters are struggling to re-establish their former numbers.
Otter biologist and science communicator Jessica Groenendijk indicates that, during the 30-odd years up to 1973, over 23,000 pelts were exported from the Peruvian Amazon, and these numbers only began to decline because the remaining populations were in areas pretty much inaccessible to hunters.
The species had been declared locally extinct in many places by the mid 20th century.
In 1973, national legislation was put in place that banned commercial hunting in Peru.
Two years later, Giant Otters were listed under Appendix 1 of CITES (Convention on International Trade in Endangered Species) – this section is reserved for species threatened with extinction.
Currently, Giant Otters are still classed as ‘Endangered’ because they face new threats in the 21st century. One of the main concerns is pollution from mining activities, which affects not only the otters but their prey and environment, too.
“The extent of gold mining in the Madre de Dios region [in Peru] increased from fewer than 10,000 hectares in 1999 to more than 50,000 hectares in 2012,” states Groenendijk.
Such a high demand for mercury in particular has resulted in vast quantities being released by the mining process into river water and sediments, contaminating all life there.
Giant Otters are also victims of poaching, overfishing, entrapment in fishing nets and habitat destruction from industries such as logging.
Conservation programmes have been put in place across South America in an attempt to help increase Giant Otter populations, including in Manu National Park in Peru and Jaú National Park in Brazil.
Photo credit: Manu Birding Lodge
Earlier this year in Argentina, as part of a rewilding project by the Conservation Land Trust of Argentina, a female Giant Otter called Alondra and a male called Lobo were introduced to Iberá National Park – a protected area spanning 160,000 hectares.
These otters are the first to return to Argentina since the species was wiped out there. By introducing more otters to these wetlands in the future, it is hoped that a stable breeding population can be re-established in Argentina.
Specialist tours where visitors hope to catch a glimpse of these amazing creatures, but without disturbing their habitat or natural behaviour, help to keep Giant Otters’ profile high.
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Giant Otter Conservation
An important area for Giant Otters is the Madre de Dios region in Peru. However, 30 percent of the riverine forests found there have been damaged, including in Protected Areas, which has led to this becoming the focus for conservation.
In May 2017, San Diego Zoo Global and the Wildlife Conservation Research Unit began an investigation in this region, assessing the impacts that factors such as gold mining and land management are having on Giant Otters.
Lead researcher Adi Barocas and his team are now involving local communities in reducing harmful activities and bringing in new management practices.
The investigation involves studying water quality, taking sediment samples and assessing the scope of mercury contamination in the study area.
The team hopes that by 2023 it can understand the effects of mercury on otters, their prey and their environment in more detail. The aim is to improve the management of water-based resources in the Madre de Dios region and work towards protecting these animals from human disturbance.
Are you interested in a Giant Otter tour?
For more information on seeing Giant Otters in the wild, check out our complete list of local wildlife specialists offering Giant Otter tours here.
Rebecca Gibson is a wildlife writer based in the UK. She is currently studying for an MA in Travel and Nature Writing at Bath Spa University and uses her blog to share her writing and photography and raise awareness of British wildlife.