The Giant Otter: Giants of the Amazon

By Jessica Groenendijk

“The charisma of these huge, Amazonian ‘river people’ burns through even the most factual descriptions, emphasized by an abundance of photographs.” —BBC Wildlife
 
The aptly named giant otter is exceptionally well adapted to life in rivers, lakes and wetlands in tropical South America. Known in Spanish as lobo del rio or ‘river wolf,’ it can be as long as a human is tall and is the most social of the world’s thirteen otter species. Each individual is identifiable from birth by its pale throat pattern, as unique as your fingerprint. Giant otters are top carnivores of the Amazon rainforest and have little to fear . . . except man.
 
There are many reasons why scientists and tourists alike are fascinated by this charismatic species. Spend a day in the life of a close-knit giant otter family and you’ll realize why. Learn about their diet and hunting techniques, marking and denning behavior, and breeding and cub-rearing strategies, including shared care of the youngest members. Become familiar with the complex life histories of individual otters over their 15-year lifespans. And accompany a young disperser during the trials and tribulations of a year spent looking for a mate and a home of its own.
 
“The descriptions of the otters, their habits and their homes along with tons of jaw dropping photographs, made me feel (almost) like I was there myself. Treat yourself to a book that will transport you to a place like nowhere else on earth, where you explore the wilds of the Amazon from your own garden.” —Cayocosta 72
 
“An intimate, educational and a dedicated love letter to the Giant Otter.” —Queen of Geekdom

• Language: English
• Publisher: Open Road Integrated Media
• Release date: Jul 30, 2019
• ISBN: 9781526711762

Jessica Groenendijk

Jessica Groenendijk is a Dutch biologist and nature writer, based in Peru. Her work in conservation has taken her from monitoring the charismatic and irrepressible giant otter in the Amazon rainforest to helping to protect endangered black rhinos in Zambia.

Book preview

2019

Introduction

There are numerous reasons why both scientists and non-scientists are fascinated by the charismatic giant otter. Confined to rainforests and freshwater wetlands in South America, this top carnivore has a complex social life, living in close-knit groups, hunting fish communally, and with older offspring helping to care for the youngest members. A giant otter family has much in common with its human counterpart, which is why observing them over many years has something of a soap opera about it. There’s sibling rivalry and play, unity in the face of a threat, shared responsibilities including babysitting and feeding of the cubs, and, finally, mature offspring leaving home and starting families of their own.

The giant otter is a carnivorous mammal that belongs to the Lutrinae subfamily, together with 12 other species of otter, and to the family Mustelidae, which also includes the weasels, badgers, martins, mink, polecats, and wolverines. In giant otter literature, the first description of the species (Pteronura brasiliensis) is attributed to a German geographer, mathematician, and naturalist, Professor Eberhard August Wilhelm von Zimmerman, in 1780. Brief but florid, and often inaccurate or exaggerated observations recorded by early Amazon explorers over the next two centuries were succeeded during the 1960s and ‘70s by more detailed publications on the diet and reproductive behaviour of captive animals.

Though wild populations of giant otters may have featured little in academic papers up to this point, on the ground in much of South America, dramatic developments were bringing this once abundant and widely distributed species to its knees. During the 1940s, ‘50s and ‘60s, giant otters became the target of the international commercial pelt trade. Skins were sold by the tens of thousands every year to luxury markets in Europe, US, and Japan, and in 1972 the IUCN Species Survival Commission (IUCN/SSC) declared the giant otter one of the ten most threatened mammals, stating that research was urgently required to determine its conservation needs.

Trade bans came into effect in most range countries between the late 1960s and mid-1970s but despite legal protection the situation was such that in March 1977 and again in 1980, the IUCN/SSC Otter Specialist Group designated the giant otter as their top priority for conservation. In 1980, Nicole Duplaix published the results of her pioneering field study into the ecology and behaviour of wild giant otters, carried out over a period of 20 months in Suriname. This was followed soon after by Liz Laidler’s 15 month doctoral study near Georgetown, Guyana; three separate field projects at Cocha Cashu, in Peru’s Manu National Park, led by Beatriz Torres, Brigitte Fugger, and Martha Brecht-Munn; a 1,600 km river population survey in El Tuparro National Park, Colombia, by Thomas Defler; and Jorge Schweizer’s extensive field observations in Brazil.

The 1990 IUCN Action Plan for Latin American Otters stated that: ‘The giant otter’s range has been greatly reduced and its diurnal, social habits, along with its size (and consequent pelt value) make it exceptionally vulnerable; the species is severely threatened…’ and continued to specify that, for Peru, a conservation priority was to ‘Monitor closely the main identified populations, particularly the giant otters of Manu National Park...’. Thus, in late 1990, the Frankfurt Zoological Society initiated what is now the world’s longest running giant otter population monitoring and conservation programme, in the Madre de Dios region of south-eastern Peru (see map overleaf). In its early years, German biologists Christof Schenck and Elke Staib both contributed doctorate dissertations to the existing body of knowledge. My own involvement in this program began in 1999 when Frank and I succeeded Christof and Elke as its coordinators. In 2006 Frank and I moved to Zambia to work with black rhinos, so it is our joint findings over the first 16 years of this program that I refer to repeatedly in this book.

Our two main study areas were the oxbow lakes and lower reaches of the Manu River (150 to 200 metres wide) in Manu National Park, and the Palma Real River and its main tributary the Patuyacu River (both 20 to 50 metres in width) in the Tambopata National Reserve, on the border of Bahuaja Sonene National Park. Both the Palma Real and the Manu are whitewater tributaries of the mighty Madre de Dios River, but the Palma Real is much smaller and lacks the oxbow lakes that characterise the Manu floodplain and are favoured by the giant otter. We conducted annual giant otter population surveys on both river systems in order to better understand their demography and conservation status.

Meanwhile, numerous other studies were initiated in Colombia, Bolivia, Ecuador, French Guiana, Paraguay, and in various parts of Brazil, including the Balbina hydroelectric reservoir, the Pantanal, and the Xixuaú Reserve, to name but a few. As a result of the increased interest in and concern for the species, the giant otter is no longer an obscure, little known animal, sought after only for its pelt. Within the space of four decades it has become a much-loved ambassador for tropical wetland ecosystems, the star of numerous articles and nature documentaries, and an outstanding model for research into important questions of evolutionary, behavioural, and conservation biology.

THE AMAZON

It seems only fitting that the world’s largest otter should make a region of superlatives its home. Named after the immense river that dominates it, the Amazon encompasses the most extensive remaining tropical rainforest in the world and shelters at least one tenth of the planet’s known biodiversity. The basin covers some 40% of the South American continent and includes parts of eight countries: Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname, and Venezuela, as well as French Guiana, a department of France. ‘If there is any place on Earth still deserving of the term ‘wilderness’ it is surely the Amazon,’ writes Dr. Lisa Davenport in her 2008 giant otter doctorate dissertation. That may well be true but the neighbouring Pantanal, to the south, comes close: at 70,000 square miles it is the world’s largest tropical wetland and boasts the highest wildlife concentration on the continent, as well as important populations of the giant otter. And then there is the Orinoco River basin, covering some 880,000 km², including most of Venezuela and eastern Colombia, and home to over 1,000 species of fish as well as the giant otter. Thus, for the sake of convenience, I am taking the liberty of using the word ‘Amazon’ in the sub title of this book as an all-encompassing name for the entire region currently inhabited by the species in South America.

THE GIANT OTTER

Giant otters are exceptionally well adapted to life in rivers, lakes and swamps of the tropical lowlands of South America. Known as lobo de rio or ‘river wolf’ in Peru, it is both the largest (at between one and a half to almost two metres in length, they are as long as a person is tall) and arguably the most social of the world’s 13 otter species. Each individual has a distinctive pale throat pattern, as unique as a fingerprint, by which it can be identified, thereby greatly facilitating field research. Giant otters are apex carnivores of the rainforest and have little to fear... except man.

Though the species is currently protected both by national legislation in all range countries as well as by the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES), its distribution has been greatly reduced and is now discontinuous, with only small, isolated populations remaining. While some of these are stable and others are even increasing, the species remains threatened throughout its distribution range: it is officially categorised in national Red Lists as Vulnerable in Brazil, Endangered or Critically Endangered in eight other countries, and Extinct in Uruguay. Giant otters face severe pressures exerted by widespread and increasing human colonisation, as well as intensive exploitation of natural resources by man, leading to the contamination and destruction of formerly pristine rainforest and wetland systems.

In the first chapter of this book we meet the giant otter; I describe its general appearance and most striking features and provide an overview of its basic ecology, behaviour, habitat, and geographical distribution. Having set the scene and introduced the main character, so to speak, we delve deeper in Chapter Two as it guides us through a day in the life of a giant otter family. In Chapter Three we accompany a disperser during the trials and tribulations of a year spent looking for a mate and a territory of its own. Chapter Four summarises past and current threats to the survival of the species. Lastly, in Chapter Five, I describe a variety of conservation actions that have benefited the otters over the last decades and propose additional steps we can take to further conservation of the species. The focus in this final chapter is largely on personal experiences and observations in south-eastern Peru, not because other countries have not undertaken conservation measures to protect the giant otter — they have — but because by using Peru as a case study I can go into rather more detail. Much of what has been, and is being achieved in Peru, can be extrapolated to other parts of the giant otter’s distribution range.

The giant otter is a top carnivore of the wetlands of Madre de Dios. The species is rare in much of its former range and extinct in Argentina and Uruguay. (ND)

In Chapters Two and Three, I have ventured to include short descriptions in italics of typical behaviour, scenery, and other wildlife from the giant otter’s perspective as I picture it to be. I am aware of the scientist’s mistrust of anthropomorphism, yet I firmly believe that animals other than ourselves experience emotions and sensations in ways that are both similar and different to ours, and that empathy and imagination only serve to increase our understanding of their worlds, while enriching our own.

Finally, I have included a personal anecdote at the end of each chapter in the hope of sharing with you the wonder, and difficulties, of life following the giants of the Amazon.

CHAPTER ONE

Meet the Giant Otter

September 1998: We slowly make our way up a small tributary of the Madre de Dios River, surveying its banks for signs of the otters. We’ve been traveling for five days without sighting a single individual, although we spotted several fresh dens this morning and know they are around. Or have we somehow passed them? Have they noticed our progress upriver and neatly taken a shortcut overland to avoid us?

As we motor past a small beach just before a sharp bend in the river, someone points out a series of giant otter footprints at the water’s edge. We stop to investigate. The tracks lead up to a marking site that has been so recently used, insects have not yet arrived at the scene. Circular sweep marks and bedraggled vegetation, leaves still wet, tell the story of how the otters have busily scent marked the beach. They can’t be far so we decide to paddle upriver rather than use the motor.

Advancing laboriously against the current, we round the curve… and there they are. Suddenly, we find ourselves in the midst of a group of five giant otters. They surge towards us from all directions, periscoping — craning their heads and necks out of the water — and snorting repeatedly, clearly alarmed to have been approached so unexpectedly. We keep as low a profile as is possible in a twelve metre canoe, avoiding abrupt movements and saying little. Gradually, their focus seems to turn inwards: the otters begin milling about, as if confused. Without warning, one individual utters a harsh, wavering scream and the whole family lets loose a burst of sound. The volume at such close quarters is stunning and sends shivers down my spine. A sixth otter who must have been hunting by himself further upriver wails in response, swimming rapidly towards the family. Once reunited, they all head downriver, giving us a wide berth and looking back frequently before disappearing from view.

APPEARANCE

On encountering a giant otter for the first time, the feature that is likely to impress you most, as its name suggests, is its size. Known through much of its range as the ‘water dog’ or ‘river wolf’, it is one of South America’s top carnivores. At 1.5 to 1.8 metres in total length, it is the largest of the world’s 13 otter species although the sea otter (Enhydra lutris) is heavier, weighing as much as 42 kilograms compared to the river wolf’s maximum of 34 kilos or so. Both sexes are ‘giants’ — in contrast to many other otter species where body size and weight differ significantly between the sexes, sexual dimorphism in giant otters is not pronounced.

This adult male giant otter is in superb condition. In the water below, on the lef, is his cub. Note its smaller head and more pronounced ears. (ND)

Not unlike a seal in appearance, the giant otter is primarily terrestrial but, like the seal, has become exceptionally well adapted to the pursuit of prey in aquatic environments. When on land, it appears hunched and clumsy due to its elongated, low body, broad pelvis, and narrow shoulders. Nonetheless, it may travel considerable (though always the shortest possible) distances between water bodies, tending to use well-worn paths. The giant otter has short, stubby legs and large feet, with five long toes and thick webbing extending to their tips. Sharp, curved claws help it grip its prey and climb steep, slippery banks. The giant’s long and supple body ends in a tail nearly half its body length, wing-shaped (hence the prefix Ptero in its scientific name), thickly muscular at the base, and dorsoventrally flattened like a beaver’s. On entering the water, the otter doggy-paddles. At high speed the undulating tail maintains momentum, while the feet are hardly used except to steer. When fishing, giant otters travel slowly, about one mile per hour, compared to an average of four miles per hour when swimming in a specific direction. When fully submerged, otters can move much faster, up to 10 miles per hour over short distances.

An adult giant otter footprint is almost the size and shape of a human hand. The interdigital webbing is just visible in this set of tracks on damp clay. (FH)

These feet are made for grasping… and swimming. Fish rarely get away once in the grip of a giant otter. (FT)

The body is covered with a pelt so fine it almost led to the river wolf’s undoing. Velvety brown when dry and shiny dark chocolate when wet, it consists of a layer of dense under-fur and a second layer of slightly longer (one centimetre), water-repellent guard hairs. An irregular pattern of pale markings on the chin, throat, and chest is unique to each individual from birth, ranging in appearance from a large, white bib to one or two tiny flecks. Rarely, a throat marking is entirely absent. It is the giant otter’s distinctive white throat marking and its larger size which distinguishes it most readily from the similarly built and sympatric Neotropical otter (Lontra longicaudis).

Having fine, dense, waterproof fur is a great thing for an otter, but it almost led to the giant’s undoing. (FH)

Without their unique throat markings, with which giant otters are identifable from birth, the work of giant otter researchers would be a lot harder. (JG)

The giant’s comparatively small head is broad and somewhat flattened, with a blunt muzzle, powerful jaws, slightly domed forehead, and supported by a long, muscular neck. Large, dark eyes and a nose pad (or rhinarium) that is completely haired, unique in the Lutrinae, are positioned well to the top of the head so the otter can breathe and look around while the rest of its body remains submerged. Giants hunt primarily by sight and can alter the curvature of the lens to see better underwater, giving their eyes a somewhat opaque, bulging appearance. Above water, they are able to recognise family members and human observers at a distance of 50 metres.

The ears are small and rounded and, together with the nostrils, may be closed to prevent entry of water while diving. Numerous stiff but sensitive whiskers on the muzzle, brow, and temples help the otter detect movement and locate its prey in muddy water. Giant otters have a keen sense of smell over distances greater than 100 metres and hearing is acute, although sound location may be poor.

The river wolf has 36 teeth (incisors 3/3, canines 1/1, premolars 4/3, and molars 1/2), with the lower premolar occasionally absent. Its bite force has not been measured but is sufficient to crack open fish skulls. Giant otters always eat their prey head first, and only large catfish are not eaten this way because of the size and hardness of their skulls. So, although a giant otter’s bite force is probably significant, it will not be in the league of a jaguar’s, and, unlike the jaguar, they are unable to break open a turtle shell.

A giant otter’s head bristles with whiskers that come in handy when chasing fish or negotiating through