Crocodiles and Dolphins in the Sundarbans: A Complete Wildlife Guide

A deep dive into the extraordinary lives, ancient lineages, and precarious futures of two of the Sundarbans’ most iconic aquatic inhabitants – the saltwater crocodile and the river dolphins of the Ganges-Brahmaputra delta.

Introduction: The Living Waters of the World’s Greatest Mangrove

There is a moment, familiar to anyone who has drifted in a small boat through the tidal channels of the Sundarbans, when the forest seems to close in on all sides — dark walls of roots and leaves, the smell of mud and salt and something indefinably ancient — and the water beneath the hull feels less like a path and more like a presence. The channels and creeks and estuaries of the world’s largest mangrove forest are not merely habitat: they are an entire world unto themselves, shadowed and labyrinthine, teeming with life invisible to the casual glance. And in those waters, two of the most remarkable and evolutionarily distinct animals on Earth make their home.

The saltwater crocodile (Crocodylus porosus) — the largest living reptile on the planet — has been hunting in the tidal estuaries of South and Southeast Asia for millions of years; its body plan is so perfectly adapted to its role that it has barely changed since the age of the dinosaurs. It rests on mudflats in the morning sun with a stillness that looks like death until it doesn’t; it slips silently into the opaque water and disappears. Its lineage stretches back further than the Sundarbans themselves, further back even than the delta that gave rise to the forest, to a time when the shapes of the continents were different and the ancestors of all living crocodilians were finding their way in a Mesozoic world.

The river dolphins of the Sundarbans — the Ganges River dolphin (Platanista gangetica) and the Irrawaddy dolphin (Orcaella brevirostris) — represent an equally remarkable biological achievement: warm-blooded mammals that, against the grain of mammalian evolution, turned away from the land and plunged into the silty, saline-tinged waters of one of the world’s most dynamic deltas. They are among the oldest cetacean lineages alive today, relics of an ancient world of marine mammals that have adapted, over immense spans of time, to the freshwater and brackish river environments of South and Southeast Asia. In the Sundarbans they are both rare and culturally significant — symbols of a living river system, indicators of ecological health, and, now, emblems of crisis.

This is the history of these two extraordinary groups of animals in the Sundarbans: where they came from, how they have lived, what they have endured at human hands, and what the future may hold for species that have survived ice ages and continental shifts but now face the most rapid and dangerous period of environmental change the planet has seen in recorded history.

The Ancient Predator — Origins and Evolutionary History of the Saltwater Crocodile

Deep Time: The Archosaur Legacy

To understand the saltwater crocodile is to understand one of the deepest narratives in vertebrate evolution. Crocodilians — the order that encompasses all living crocodiles, alligators, caimans, and gharials — are the sole surviving members of the Archosauria, alongside birds. Together, these two groups are the last representatives of the dominant vertebrate lineage of the Mesozoic Era, the age that includes the entire reign of the dinosaurs. The earliest crocodilians evolved approximately 95 million years ago in the Late Cretaceous period, and the living crocodiles and alligators we see today are descended from those prehistoric ancestors with a fidelity of form that is almost uncanny. Modern crocodilians and birds are, together, the closest living relatives of the dinosaurs — a fact that makes the sight of a saltwater crocodile basking on a Sundarbans mudflat a glimpse, however tenuous, of a biological world that predates our own epoch by tens of millions of years.

The genus Crocodylus — the true crocodiles — evolved in the Oligocene Indo-Pacific roughly 25.5 to 19.3 million years ago, making them geologically recent within the broader crocodilian lineage but still ancient by any human measure. Phylogenetic research suggests that Crocodylus likely originated in Africa and subsequently radiated outward, with dispersal across ocean basins — a feat made possible by the saltwater crocodile’s extraordinary tolerance for marine conditions. Fossil remains of saltwater crocodiles have been excavated in northern Queensland and dated to the Pliocene, confirming a long evolutionary presence in the Indo-Pacific region. The scientific name Crocodylus porosus was formally proposed by Johann Gottlob Theaenus Schneider in 1801, based on a zoological specimen, though the animal itself had been familiar to human societies across its range for millennia.

The saltwater crocodile is the sister taxon — the closest evolutionary relative — of both the Nile crocodile and the Siamese crocodile, and its capacity for long-distance ocean travel, using marine currents as a passive transport system, is what has allowed it to colonise island chains and coastal habitats from the Indian subcontinent to northern Australia and even Micronesia. This is not metaphor: individual saltwater crocodiles have been tracked travelling hundreds of kilometres through open ocean, and scientists believe this oceanic vagility is precisely what allowed the species to achieve its extraordinary geographic range.

The Saltwater Crocodile’s Remarkable Biology

The saltwater crocodile’s success as a species is inseparable from its physiology. It is, first and foremost, a supreme opportunist. Males grow to lengths of up to 6 metres and weights of 1,000 to 1,500 kilograms, making them the largest living reptile on Earth — and one of the most formidable predators in any ecosystem they inhabit. Females are substantially smaller, rarely exceeding 3 metres. The species’ common name is somewhat misleading: while it is the only crocodilian capable of spending extended periods in saltwater — sustained by specialised lingual salt glands that actively excrete excess salt from the blood, a feature absent in alligators and most other crocodilian species — the saltwater crocodile is equally at home in freshwater rivers and brackish estuaries. This physiological versatility makes it perfectly suited to the complex salinity gradient of the Sundarbans, where freshwater from the Ganges system mixes continuously with saline tidal water from the Bay of Bengal.

The crocodile’s sensory apparatus is extraordinary. Eyes and nostrils placed high on the head allow the animal to breathe and observe while almost completely submerged — a body plan unchanged in its essentials for tens of millions of years. Three eyelid systems provide layered optical protection: two leathery eyelids for physical protection and a clear nictitating membrane that sweeps across the eye during underwater hunting, providing vision without exposure to debris. Crocodiles can reduce their heart rate dramatically during aerobic dives, extending their capacity to remain submerged; some individuals can hold their breath for up to nine hours in extreme circumstances. The jaw muscles of a large saltwater crocodile generate some of the most powerful bite forces of any living animal — though, as with all crocodilians, the muscles that open the jaw are relatively weak, meaning a human can physically hold a crocodile’s mouth shut if strong enough to grip it.

Saltwater crocodiles in the Sundarbans inhabit coastal brackish mangrove channels and river deltas, preferring waterways with widths less than 170 metres, where sightings are most frequent. They are ectothermic — cold-blooded in the conventional sense — and regulate their body temperature through behaviour rather than metabolism. In the Sundarbans, they are most commonly observed basking on mudflats and riverbanks during morning hours, absorbing the sun’s warmth to raise their body temperature for the day’s activities. Maximum sightings occur at ambient temperatures around 22.7 degrees Celsius, slightly above the water surface temperature.

As apex predators of the Sundarbans’ aquatic ecosystem, saltwater crocodiles play an irreplaceable ecological role. They take almost any prey item they can overpower — fish, crustaceans, water birds, deer and other mammals that come to drink at the water’s edge and, historically, humans. They are also carrion consumers, feeding on carcasses and thereby helping to clear the waterways of organic material that would otherwise degrade water quality. In the Sundarbans, they share apex predator status with the Royal Bengal Tiger, and the two species occasionally interact at the water’s edge in an ecological drama that draws from the deepest roots of predator-prey dynamics in the mangrove world.

The crocodile’s reproductive biology is as ancient as its body plan. Estuarine crocodiles in the Sundarbans begin courtship between September and October, mate during the rainy season, and have females lay eggs between November and March. Nesting females construct mound nests from decaying vegetation, relying on the heat of decomposition as well as ambient temperature to incubate their eggs — a strategy that demonstrates an intimate evolutionary partnership between the reptile and the plant material of its mangrove environment. Females guard their nests fiercely and are among the most attentive of reptile parents, assisting hatchlings to emerge and carrying them to the water in their jaws with a tenderness that stands in jarring contrast to their reputation as fearsome predators.

The Crocodile in History — Presence, Persecution, and Near-Extinction

Before the Colonial Era: Crocodiles as Part of the Sundarbans’ Fabric

Long before any recorded human documentation, saltwater crocodiles were a fundamental element of the Sundarbans’ ecology—senior inhabitants of the tidal delta in a lineage that far predates the mangrove forest itself. For the communities that have historically lived at the edges of the Sundarbans, fishing in its channels and harvesting its forest products, the crocodile was not an abstraction but an immediate and daily presence: a risk to be managed, a creature embedded in local folklore, and an animal whose movements and habits the most experienced river workers learned to read as carefully as the tides.

The crocodile’s place in South Asian cultural imagination is ancient and complex. In Hindu mythology, the makara — a composite sea creature typically depicted with a crocodilian body — is the vahana (vehicle) of the river goddess Ganga and of the deity Varuna, the lord of waters. The association of the crocodile with sacred rivers runs deep through the subcontinent’s religious traditions, speaking to the animal’s long co-existence with human riverine cultures. In the Sundarbans specifically, local folklore preserves traditions about the crocodile’s power and danger, with communities of fishers and honey collectors developing elaborate protocols for entering the water – certain times of day, certain seasons, certain stretches of channel – that encoded generations of observation about when and where crocodiles were most likely to strike.

The oral tradition of the Sundarbans is rich with the crocodile’s presence. The Bonbibi cult — the forest goddess who protects human beings from the twin dangers of the tiger and the crocodile — reflects the way in which these two apex predators structured human life and spiritual practice in the delta for centuries. Before entering the forest or the water, fishers and woodcutters would invoke Bonbibi and her brother Shah Jongoli for protection, acknowledging implicitly that they were entering a world governed by forces older and more powerful than themselves. The crocodile in this tradition is not merely a physical hazard but a cosmological entity — a guardian of the water’s boundary between the human world and the wild.

The Colonial Assault: Hunting, Fear, and Commercial Exploitation

The arrival of British colonial administration in the Sundarbans brought a profoundly different relationship with the crocodile. Where indigenous communities had developed systems of coexistence – pragmatic, spiritually inflected, and respectful of the animal’s power – the colonial perspective was primarily one of threat and resource. The crocodile, like the tiger, was viewed as an obstacle to development: a predator that attacked labourers clearing forest for agricultural land, a danger to the fishing communities whose output the colonial economy depended on, and a creature whose valuable skin represented a commercial opportunity.

Throughout the 19th and early 20th centuries, the systematic hunting of saltwater crocodiles in the Sundarbans and across the Indian subcontinent proceeded with little regulation. Crocodile hunting was encouraged as a form of pest control — colonial records document bounties paid for crocodile kills in various parts of British India, similar to the bounties paid for tigers. The crocodile’s reputation as a man-eater gave moral cover to campaigns of extermination; in a colonial framework that prioritised agricultural productivity and the safety of the workforce above biodiversity, the crocodile was cast as an enemy of progress.

Through the first half of the 20th century, a new and even more destructive force joined the old narrative of fear: the international commercial trade in crocodile skins. By the mid-20th century, the global fashion industry had created an insatiable demand for exotic leather goods — handbags, shoes, belts, and briefcases made from the belly skins of large crocodilians. Saltwater crocodile skin, with its distinctive regular scales and deep lustre, was among the most commercially valuable materials in the luxury goods trade. Hunters across the species’ range pursued Crocodylus porosus with rifles, traps, and electrofishing gear. Eggs were stolen from nests; hatchlings were taken for the trade. The combination of fear-driven persecution and commercial exploitation drove saltwater crocodile populations across South Asia to the verge of annihilation.

In India, the consequences were catastrophic. Overexploitation, poaching, and unregulated hunting caused a major decline in the saltwater crocodile population across the entire subcontinent through the 1950s and 1960s. By the late 1960s, the saltwater crocodile had been hunted to extinction in Kerala, Tamil Nadu, and Andhra Pradesh — states that had historically supported robust populations. Only in two places did the species survive in any meaningful numbers: Bhitarkanika on the Odisha coast and the Sundarbans. The Sundarbans’ relative remoteness, its impenetrable tidal forest, and the practical difficulties of moving through its labyrinthine waterways offered the crocodile a refuge that more accessible habitats could not. Even here, populations were severely reduced — shadows of what they had once been.

In Bangladesh, the situation was equally grim. Commercial exploitation for skins until the 1970s decimated populations across much of their historical range. The saltwater crocodile was effectively gone from most of its former Bangladesh haunts. Today, known populations are confined to the Sundarbans delta, where even at their post-conservation recovery numbers, they remain low — the most recent surveys estimated approximately 140 mature individuals in the Bangladesh Sundarbans.

The extinction of the mugger crocodile (Crocodylus palustris) from the Sundarbans adds another dimension to this story of loss. The mugger — a broad-snouted freshwater crocodile historically found across South Asia — had inhabited the fringes of the Sundarbans ecosystem, occupying the slightly higher-salinity-tolerance zone between the purely freshwater inland environment and the saltwater-dominated tidal channels. It was declared effectively extinct in Bangladesh during the 20th century, a casualty of the same forces of habitat destruction and persecution that have reshaped the Sundarbans’ fauna across the past two centuries. Some species whose names once appeared in old documents of the Sundarbans – the Javan rhinoceros, wild water buffalo, swamp deer, and hog deer – have vanished entirely, extirpated as the forest was cleared, fragmented, and hunted over generations.

Recovery, Conservation, and a Tentative Return

Project Crocodile: India’s Conservation Awakening

The turning point for saltwater crocodile conservation in India came in the early 1970s, when the scale of the species’ decline became impossible to ignore. In 1972, the Wildlife (Protection) Act was passed, listing the saltwater crocodile as a Schedule I species — the highest category of legal protection, theoretically making it illegal to kill, capture, or trade in the animal. This legal protection, however, needed to be backed up by active management if populations so severely reduced were to have any realistic chance of recovery.

In 1974, the United Nations Development Programme (UNDP) and the Food and Agriculture Organization (FAO), in partnership with the Government of India, initiated a saltwater crocodile conservation programme — initially known as ‘Baula’ — in Bhitarkanika National Park. The following year, in 1975, India launched its Crocodile Conservation Project in earnest, a landmark initiative that also extended to gharials and mugger crocodiles. The project operated on a “rear and release” model: eggs were collected from wild nests, hatched in protected facilities, and the resulting hatchlings reared in captivity through the most dangerous early months of their lives before being released into protected wild habitat. This approach addressed the most vulnerable phase of the crocodilian life cycle — when mortality from predation and environmental hazards is highest — and allowed rapid population growth that would have been impossible with purely wild reproduction.

For the Sundarbans specifically, the Bhagabatpur Crocodile Project was established in 1976, located in South 24 Parganas district in West Bengal, next to the uninhabited Lothian Island on the bank of the Saptamukhi Estuary. The project’s goals were clear and urgent: increase the severely depleted saltwater crocodile population of the Sundarbans through captive breeding and supplementary release. The facility was constructed with six breeding pools of different sizes and 14 enclosures with water tanks for housing hatchlings of different age groups, along with a dedicated hatchery. It quickly became one of the most important crocodile conservation facilities in India — indeed, one of the few dedicated crocodile breeding centres in the world.

From 1982 onwards, the project began collecting eggs from within the facility itself rather than from wild nests, establishing a self-sustaining breeding programme. Over the following four decades, the Bhagabatpur Crocodile Project bred and released 577 saltwater crocodiles — approximately 629 individuals by various counts, with the project reporting 312 animals released into the wild rivers of the Sundarbans by 2012 alone. These released animals, typically 1 to 1.5 metres in length and three years of age — old enough to have a reasonable survival probability in the wild but young enough to establish themselves in the ecosystem — formed the nucleus of the Sundarbans’ recovering crocodile population.

The results of this sustained effort have been gratifying, if sobering in their demonstration of how much ground has yet to be recovered. By 2025, the saltwater crocodile population of the Indian Sundarbans Biosphere Reserve was estimated at between 220 and 242 individuals, with 213 direct sightings recorded during the most recent systematic census – a significant increase from the 204 to 234 estimated in earlier surveys and a particularly encouraging sign of hatchlings, which are rarely observed in this difficult terrain. In Bangladesh, the most recent assessments estimated approximately 140 mature individuals in the Sundarbans, with an encounter rate of just 0.12 individuals per kilometre of river surveyed — a figure that starkly illustrates the thinness of the population even after decades of protection.

India celebrated the 50th anniversary of the Crocodile Conservation Project in 2024 — World Crocodile Day that year, marking the milestone with renewed surveys and positive reports from multiple conservation sites. The saltwater crocodile count at Bhitarkanika National Park reached 1,811 in 2024, a marginal but encouraging rise, while the Sundarbans figures followed their own positive trajectory. Together, these developments underscore the value of sustained, long-term conservation investment — though they also illuminate the fragility of recovery in populations that remain far below their historical abundances.

The Ecological Complexity of Human-Crocodile Coexistence

The recovery of saltwater crocodiles in the Sundarbans is not an unambiguous story of triumph, because the forest is not a wilderness empty of human beings. Approximately 7.2 million people live in and around the Sundarbans, many of them deeply poor and dependent on the waterways for their livelihoods as fishers, crab harvesters, and shrimp farmers. For these communities, the return of the crocodile is not simply an ecological victory — it is also a source of danger and conflict that must be carefully managed.

Research on human-crocodile conflict in the Indian Sundarbans has identified clear patterns in the spatio-temporal distribution of attacks. Fishing and crab collection are the activities that most frequently bring humans and crocodiles into contact, particularly in the narrow tidal creeks where the crocodiles most often concentrate. Women who collect shellfish and crabs along the water’s edge are sometimes disproportionately affected. The encroachment of rising salinity — exacerbated by Cyclone Aila in 2009 and Cyclone Amphan in 2020 — has driven crocodiles into areas they had not previously occupied, including village ponds, as the mangrove creeks they normally inhabit become physiologically marginal. Researcher Ujjwal Sardar noted that rising sea salinity in the Sundarbans is increasingly driving crocodiles into villages and village ponds, creating conflict situations that were previously rare.

Managing this human-crocodile interface is one of the most difficult challenges facing conservation authorities in the Sundarbans. Unlike tigers, which can theoretically be kept from human settlements through fencing and early warning systems, crocodiles are aquatic animals that cannot be excluded from waterways that human beings depend on for their livelihoods. A large number of crocodiles — both juveniles and adults — are still poached from the Sundarbans each year, with skins used to make luxury items and meat and eggs consumed locally. The Forest Department works to prevent this poaching, but with limited resources across a vast and difficult-to-monitor landscape, success is partial at best.

The Bhagabatpur facility now also receives rescued crocodiles — animals that have strayed into human-inhabited areas and been captured by authorities — providing a holding and rehabilitation space that reduces the likelihood of conflict-driven killing. The facility itself has become an important ecotourism destination, offering visitors a chance to see crocodiles at close range in a managed setting — revenue that can be channelled back into the conservation programme and provides economic justification for the project’s continuation beyond pure ecological rationale.

The Threats Ahead: Climate Change and the Crocodile’s Uncertain Future

While the saltwater crocodile’s conservation trajectory in the Sundarbans has been more positive than for many species, serious threats remain — and new ones are emerging. The rise in salinity levels across the Sundarbans, driven by reduced freshwater inflow from the Ganges-Brahmaputra system and accelerating sea-level rise, could potentially reduce suitable habitat areas for the crocodiles by altering the distribution of the mangrove communities on which they depend for shelter and nesting cover.

Cyclones represent another acute threat. The 2021 Cyclone Yaas caused significant damage to the Bhagabatpur Crocodile Breeding Centre, with the facility submerged and approximately 300 crocodiles temporarily at risk. While the animals survived the event, it underscored the vulnerability of captive conservation infrastructure to increasingly frequent and intense cyclone events. The nest mounds that female crocodiles construct in the Sundarbans’ mangrove root systems are equally vulnerable to storm surge inundation, which can destroy entire clutches of eggs in a single event.

Heavy metal pollution — from industrial discharges, agricultural runoff, and shipping traffic — accumulates in the bodies of animals at the top of the aquatic food chain, a process known as biomagnification. As apex predators that consume large quantities of fish, crustaceans, and other wildlife, saltwater crocodiles are likely accumulating significant loads of pollutants, though systematic monitoring of contaminant levels in the Sundarbans crocodile population remains limited. Oil spill events, like the 2014 tanker sinking in the Shela River in Bangladesh, can cause acute damage to the aquatic habitat and prey base that crocodiles depend on.

The Ancient Swimmers — Origins and Biology of the Sundarbans’ Dolphins

From Sea to River: The Evolutionary Journey of River Dolphins

The presence of dolphins in the silty, tidal waters of the Sundarbans seems, at first glance, improbable. Dolphins are mammals — warm-blooded, air-breathing, socially complex creatures whose ancestors spent their lives on land. The return of early cetaceans to the water, beginning approximately 50 million years ago, is one of the most dramatic evolutionary transitions in the history of vertebrate life: land-dwelling mammals that progressively re-adapted to aquatic existence, losing their limbs, developing tail flukes and streamlined bodies, refining sonar systems for navigation in murky water, and ultimately becoming among the most sophisticated swimmers on Earth.

The Ganges River dolphin (Platanista gangetica) occupies a particularly ancient branch of the cetacean family tree. Along with the Indus River dolphin, it constitutes the family Platanistidae — a group so divergent from all other living cetaceans that it is placed in its own superfamily. The Platanistidae are considered living fossils: direct representatives of an ancient lineage of river dolphins that was once widespread across the world’s oceans and river systems but has been reduced, through the vicissitudes of climate and geography, to just two species in the rivers of South Asia. The taxonomy was revised in 2021 so that the Ganges and Indus populations are now recognised as two separate species rather than subspecies of a single animal – a revision that elevates the conservation urgency for each remaining population.

The evolutionary isolation of Platanista is extraordinary. These animals are not closely related to the river dolphins of South America (the boto), the Yangtze river dolphin (now functionally extinct), or the Irrawaddy dolphin – each of which represents an independent evolutionary experiment in the occupation of freshwater environments by cetaceans. The Platanistidae diverged from the marine dolphin lineage tens of millions of years ago and have been evolving in isolation in the rivers of South Asia ever since. In this sense, the Ganges River dolphin is genuinely irreplaceable: if it goes extinct, there is nothing else like it anywhere on Earth.

The Ganges River dolphin’s adaptations to its river environment are profound. Unlike marine dolphins, Platanista is effectively blind — its eyes are highly vestigial, lacking a crystalline lens and capable of detecting only light and dark rather than forming images. This is not a loss but an adaptation: in the silty, turbid waters of the Ganges-Brahmaputra system, where visibility is often zero, eyes are largely useless. Instead, the Ganges dolphin relies almost entirely on echolocation — a sophisticated biosonar system that allows it to build a detailed acoustic map of its surroundings, locate fish and other prey in complete darkness, and navigate the complex channels of the delta with astonishing precision. The animal continuously emits clicking sounds and processes the returning echoes with a neural apparatus of extraordinary sensitivity. Ganges River dolphins are often called “susu”—a name derived in many South Asian languages from the distinctive sound they make when they breathe at the surface, a characteristic that made them recognisable and memorable to human communities living along the rivers long before formal science took notice.

The Irrawaddy dolphin (Orcaella brevirostris) represents a completely different evolutionary pathway. Unlike the Ganges dolphin, which belongs to an ancient exclusively freshwater lineage, the Irrawaddy dolphin is descended from fully marine oceanic dolphins and has, more recently in evolutionary terms, colonised brackish and freshwater environments. The name is derived from the specimens first described from the Ayeyarwady (Irrawaddy) River in Myanmar, though the species ranges across a wide swath of coastal and estuarine habitats from India through Southeast Asia. The Irrawaddy dolphin’s relationship with the Sundarbans is one of relatively recent evolutionary colonisation: marine Irrawaddy dolphins that had been exploring rivers in search of fish found good fishing opportunities away from the competition of other marine dolphins, and over many generations, some populations established themselves permanently in brackish and freshwater habitats, gradually adapting to the changed conditions of the delta environment.

The Irrawaddy dolphin’s appearance is striking and distinctive: a rounded, blunt head with no obvious beak; a flexible neck with visible creases; slate-blue to slate-grey colouring, paler on the belly; long, paddle-shaped flippers with curved leading edges; and a body reaching 180 to 275 centimetres in length and weighing between 90 and 200 kilograms. The flexible neck – unusual among dolphins – gives the Irrawaddy dolphin an expressive, almost doll-like quality that has made it a popular animal in captivity across Southeast Asia, tragically contributing to unsustainable collection from wild populations. Its teeth, resembling pegs rather than the sharp conical teeth of most dolphins, reflect a diet that includes small fish and invertebrates caught in the shallow, turbid waters of estuaries and mangrove channels.

Both dolphin species share a fundamental characteristic that makes them particularly vulnerable in the Sundarbans context: they are deeply sensitive to water quality, salinity, and the availability of freshwater flows. The Ganges River dolphin is strictly dependent on freshwater — it cannot survive in high-salinity conditions for extended periods and retreats from the tidal zone of the Sundarbans during the dry season when saltwater penetration is greatest. The Irrawaddy dolphin is somewhat more tolerant of brackish conditions — it is described as a euryhaline species, capable of occupying marine, brackish, and freshwater environments — but even it has clear preferences for low-salinity, shallow, turbid waters. Both species are tied, ultimately, to the health of the river system upstream: to the volume and quality of freshwater flowing down from the Himalayan headwaters through the Ganges-Brahmaputra system and into the delta.

Dolphins in Human History — Documentation, Mythology, and Decline

The First Records: Mythology, History, and Science

The Ganges River dolphin has swum through South Asian consciousness for at least as long as the civilisations of the subcontinent have existed. In Hindu tradition, the dolphin is associated with the river Ganga herself — the sacred river personified as a goddess and regarded as the most spiritually significant waterway on Earth. The dolphin’s presence in the Ganga was understood as a mark of the river’s vitality and sanctity. Folk tales across the Gangetic Plain attribute human qualities to the dolphin, and in some traditions it is believed that the dolphins are the spirits of ancestors. This deep cultural embeddedness provided a degree of informal protection – communities that regarded the dolphin as sacred or as an ancestor were unlikely to harm it deliberately.

The first scientific documentation of the Ganges River dolphin in the Sundarbans region dates to 1801, when William Roxburgh, superintendent of the Botanical Garden in Calcutta, documented the occurrence of the species in the Hooghly River — the distributary of the Ganges that flows past Calcutta and through the western Sundarbans. The animal was formally described scientifically in 1801 as Delphinus gangeticus by both Heinrich Julius Lebeck and William Roxburgh, with a type specimen caught near Calcutta in late 1797 and sent to the Hunterian Museum in London. Records from 1879 document the freshwater-loving mammals swimming along the entire length of the Sundarbans waterway system — a presence that was at that time evidently abundant enough to be unremarkable.

The Irrawaddy dolphin in the Sundarbans context is somewhat more recently documented in the scientific literature, though it has long been familiar to local communities. A 2006 survey by the Wildlife Conservation Society identified 451 Irrawaddy dolphins in the Bangladesh Sundarbans — a figure that at the time seemed encouraging but which would soon reveal itself as a benchmark of decline rather than a population in good health.

The Farakka Barrage and the Fragmentation of Dolphin Habitat

The most catastrophic single human intervention affecting dolphins in the Sundarbans has arguably been the construction and operation of the Farakka Barrage on the Ganges River in India. Completed in 1975 and commissioned specifically to divert a portion of the Ganges’ flow into the Hooghly River to maintain the navigability of Calcutta’s port, the Farakka Barrage has had consequences that extend far beyond its immediate engineering purpose.

For the Ganges River dolphin, the barrage was devastating. In 1975, when the Farakka Barrage was commissioned, the dolphins in the main channel of the Ganga were split into two subpopulations that can no longer interbreed — a genetic and demographic fragmentation that has weakened both groups. Subsequently, the Lower Ganga Barrage at Narora (commissioned in 1966) and the Middle Ganga Barrage at Bijnor (1984) further fragmented the Ganga mainstem population into four subpopulations bounded by the barrages. Today, dolphins have been extirpated from above the Middle Ganga Barrage at Bijnor entirely — gone from stretches of river they once occupied in abundance.

The Farakka Barrage’s effects on the Sundarbans dolphins are felt through a second mechanism as well: the diversion of Ganges water reduces the volume of freshwater reaching the western Sundarbans during the dry season, dramatically increasing salinity throughout the tidal river system. Water diversion and commissioning of large barrages upstream have greatly influenced the salinity profile of the rivers downstream in the central Sundarbans, which lose their freshwater supply for much of the year. Historically, the Ganges River dolphin was documented in waterways throughout the Sundarbans system. Today, rising salinity has pushed the species out of large portions of its former Sundarbans range — it is rarely visible in the waterways of the Indian Sundarbans, increasingly confined to the less saline northeastern portions of the delta where freshwater influence remains stronger.

India’s ecologist Ravindra Sinha — known as “India’s Dolphin Man” — has observed that earlier one could spot Ganges dolphins in the entire Sundarbans, including different water channels, tributaries, and distributaries, but rising salinity has progressively eliminated the species from much of this former range.

The Collapse of Dolphin Populations: A Numbers Story

The numbers tell a sobering story of loss. A survey in 2001 by the Wildlife Conservation Society Bangladesh found 225 Ganges dolphins in the Sundarbans areas with lower salinity. By a subsequent survey conducted between January and April of a more recent year, that population had declined to just 159 individuals – a reduction of nearly 30 per cent in the span of a few years. For the Irrawaddy dolphin in Bangladesh’s Sundarbans, the 451 individuals identified in 2006 had fallen to just 198 by the most recent comprehensive survey — a population halved in little more than a decade.

These numbers place both species in genuine crisis. The International Union for Conservation of Nature (IUCN) classified the Irrawaddy dolphin as ‘Endangered’ in 2017, with the assessment taking note of the staggering 50 per cent reduction in population over the preceding 10 years. For the Ganges river dolphin — India’s National Aquatic Animal — the overall range-wide population was estimated at 4,000 to 5,000 animals in the early 1980s, declining to approximately 3,500 by 2014, with projections continuing downward. The most recent estimates put the current Indian population at fewer than 2,000 individuals.

Globally, the picture for Irrawaddy dolphins is even more alarming in many of its river populations. Most river populations of Irrawaddy dolphins number fewer than 100 individuals and are still declining; in some isolated freshwater populations — the Mekong, the Mahakam, and the Ayeyarwady — extinction within human lifetimes now seems the likely outcome without radical intervention. While the Sundarbans population of Irrawaddy dolphins is larger than these isolated river groups, and Bangladesh supports what is believed to be the world’s largest population of Irrawaddy dolphins, numbering about 6,000 individuals along its entire southern coast, including the Sundarbans, the trajectory of decline within the Sundarbans itself is deeply concerning.

The Web of Threats: What Is Killing the Dolphins?

The forces driving dolphin decline in the Sundarbans are multiple, interacting, and difficult to disentangle. No single factor can be identified as the sole cause of the crisis — instead, the dolphins face what conservation biologists call a “threat web”: a matrix of pressures, each of which might be individually manageable but which, in combination, are proving lethal.

Gillnet Entanglement: Entanglement in small-scale fishing nets — particularly the monofilament gillnets that are standard equipment for subsistence fishers throughout the Sundarbans — is consistently identified as the single biggest immediate cause of dolphin mortality. Both Ganges River dolphins and Irrawaddy dolphins become tangled in these invisible underwater traps and drown, unable to surface to breathe. Fourteen Ganges and Irrawaddy dolphins were confirmed to have died after being caught in fishing nets in the Sundarbans over a recent six-year period — and this almost certainly represents a fraction of the true mortality, since many net-caught dolphins are not reported. The problem is particularly acute because the fisheries involved are not industrial but subsistence operations, carried out by desperately poor communities for whom any restriction on fishing methods represents a direct threat to their food security and income.

Pollution and Water Quality Degradation: The waterways of the Sundarbans receive industrial effluents, agricultural runoff laden with pesticides and fertilisers, domestic sewage, and the cumulative impacts of heavy shipping traffic. Contaminants, including organochlorine pesticides, heavy metals, and petroleum products, accumulate in the fat of cetaceans – biomagnifying through the food chain. Six Irrawaddy dolphin populations globally have been found to show high levels of skin abnormalities thought to be associated with poor water quality. The 2014 oil spill in the Shela River — when an oil tanker sank in the Bangladesh Sundarbans, releasing hundreds of tonnes of furnace oil into the river system — killed or injured crocodiles and dolphins, coated mangrove roots, and disrupted the food web on which both species depend.

Maritime Traffic: The Sundarbans is not a remote wilderness; it is criss-crossed by vessel traffic ranging from small wooden fishing boats to large cargo ships and oil tankers serving the ports of Khulna and Mongla in Bangladesh. Noise pollution from engine noise drowns out the echolocation clicks that dolphins use to navigate and communicate, disorienting them and impairing their ability to detect food and avoid hazards. Physical collisions between vessels and dolphins cause direct injury and death. The continued passage of large vessels carrying oil through declared dolphin sanctuaries has been identified as a significant and ongoing threat.

Salinity Intrusion: Rising salinity, driven by reduced freshwater inflow and sea-level rise, is eliminating suitable habitat for the freshwater-dependent Ganges River dolphin at a pace that threatens to remove the species from the Sundarbans entirely. Healthy dolphins need daily access to water within their physiological salinity tolerance range; as the freshwater corridor connecting the Sundarbans to the main Ganges-Brahmaputra channels shrinks, dolphins are squeezed into smaller and smaller areas. The Irrawaddy dolphin, while more tolerant of salinity variation, also shows a clear preference for lower-salinity conditions and is affected by the progressive salinization of the delta.

Poaching and Direct Exploitation: While large-scale commercial hunting of dolphins is now illegal throughout the Sundarbans region, targeted poaching continues. Dolphin oil — rendered from blubber — is used as a fish attractor by some fishers and has historically been used in traditional medicine. Dolphins are occasionally killed deliberately when they damage fishing nets or compete with fishers for fish. The illegal trade in dolphin products, while smaller in scale than the threats from bycatch and habitat degradation, adds mortality pressure on already small populations.

Conservation Responses — Sanctuaries, Science, and the Search for Solutions

Dolphin Sanctuaries in the Sundarbans

Recognising the severity of the threat to its cetacean inhabitants, the Bangladesh government has established several dolphin sanctuaries within the Sundarbans Reserved Forest — specific stretches of waterway declared as safe havens where fishing is strictly prohibited, and vessel traffic is restricted. These sanctuaries represent an attempt to protect the most critical dolphin habitats — the channels and confluence zones that surveys have identified as dolphin hotspots — from the most immediate human pressures.

The principle behind the dolphin sanctuary approach is sound: if the areas of highest dolphin use can be protected from gillnet fishing and disruptive vessel traffic, the mortality rate can be reduced enough to allow population stabilisation and potentially growth. Research by the Wildlife Conservation Society and other organisations has identified dolphin hotspots in the eastern Sundarbans mangrove waterways in Bangladesh, providing the scientific basis for locating sanctuaries where they will have the greatest conservation impact.

However, the implementation of sanctuary protections faces serious challenges. Enforcement across the vast and fragmented waterway network of the Sundarbans is logistically daunting — the forest department has limited personnel, limited boats, and a huge area to monitor. Fishing communities whose livelihoods depend on the prohibited waterways may continue to operate illegally when enforcement is absent. Large vessel traffic continues through some sanctuaries, since the economic and logistical costs of rerouting commercial shipping are substantial. And the continued passage of oil tankers through dolphin sanctuary waters — a threat that has been explicitly identified but not yet resolved — represents an ongoing source of risk that sanctuary designation alone cannot address.

Conservation activities more broadly include research programmes to better understand dolphin distribution and ecology; community awareness and education initiatives aimed at changing attitudes and behaviours among fishing communities; advanced patrolling to minimise wildlife crime; and policy advocacy at the national and international level. The Bangladesh Dolphin Action Plan 2020-2030, published in 2019, provides a framework for coordinated conservation action across the country, including specific provisions for the Sundarbans population.

The Role of Science: Monitoring and Understanding

Better scientific understanding of dolphin distribution, behaviour, and ecology in the Sundarbans has been a critical foundation for conservation planning. Vessel-based line transect surveys — in which trained observers count dolphins from a moving research boat travelling along systematically chosen routes — have provided the population estimates that document both the current status of Sundarbans dolphin populations and the alarming trends in their decline. Acoustic monitoring, using hydrophones to detect the echolocation clicks of dolphins, can document presence and activity even when animals are not visible at the surface, providing more comprehensive data on habitat use.

The recognition that Irrawaddy dolphin distribution is closely tied to specific environmental parameters — particularly low salinity and shallow water depth — has informed the targeting of conservation efforts toward the habitat characteristics that matter most for the species. A 2009 study on habitat selection of freshwater-dependent cetaceans in the Sundarbans found that Irrawaddy dolphin distribution was significantly dependent on low salinity, with this single variable explaining 36 per cent of the variance in occurrence patterns. This finding has direct management implications: the most important thing that can be done to protect Irrawaddy dolphins in the Sundarbans, beyond reducing direct mortality from fishing nets, is to maintain the freshwater flow that sustains low-salinity conditions in the channels they depend on.

The Intertwined Fates of Crocodile and Dolphin in a Changing Sundarbans

Sharing the Waters: Ecological Interactions

It is one of the more remarkable ecological relationships in the Sundarbans that two such evolutionarily distant animals as the saltwater crocodile and the river dolphin should share the same waterways — the ancient reptilian apex predator and the ancient cetacean. While direct predation of dolphins by crocodiles is not commonly documented, the two groups occupy overlapping habitats, particularly in the smaller tidal channels and creek systems where both concentrate. Large saltwater crocodiles are theoretically capable of attacking a dolphin that ventured too close in shallow water, and the dolphins’ sophisticated echolocation would presumably allow them to detect and avoid crocodiles under most circumstances.

Both the crocodile and the dolphins serve as what ecologists call “umbrella species” or “indicator species” — animals whose presence, abundance, and health reflect the overall quality of the aquatic ecosystem. When saltwater crocodile numbers recover, it indicates that the tidal habitat is sufficiently intact to support the species at the apex of the food web. When dolphin populations decline, it signals deterioration in the water quality, freshwater flows, and fishing pressure that sustain the entire river ecosystem. Monitoring these two charismatic species provides wildlife managers with a window into the health of the Sundarbans waterways that would take far more resources to assess through comprehensive ecological monitoring of all species.

The crocodile’s role as a scavenger and consumer of large prey contributes to nutrient cycling in the tidal waterways — carcasses consumed by crocodiles are broken down and their nutrients returned to the water column and sediment in ways that support the broader food web. The dolphins’ fishing activities concentrate in productive areas of the waterway network, and their presence has historically guided fishers to productive fishing grounds — a form of ecological knowledge embedded in traditional fishing practice across South Asia. Both species are embedded in the cultural as well as ecological life of the Sundarbans and have shaped the way human communities have understood and related to the delta across generations.

The Shared Crisis: Climate Change and Both Species’ Futures

For both the saltwater crocodile and the river dolphins of the Sundarbans, the accelerating impacts of climate change represent an overlapping and reinforcing set of threats. Rising salinity — the consequence of reduced freshwater inflow and sea-level rise — eliminates habitat for the freshwater-dependent dolphins directly and may push crocodiles into conflict with human communities as their preferred habitat shifts. More frequent and more intense cyclones damage breeding habitat for both crocodile nests in mangrove root systems, which are vulnerable to storm surge inundation, and the immediate aftermath of a major cyclone brings toxic concentrations of debris, chemical runoff, and disrupted prey communities that are hostile to dolphins.

The projected loss of 42 to 80 per cent of the Indian Sundarbans mangrove area by the end of this century under various sea-level rise scenarios, as modelling studies have suggested, would represent an existential change for both species. Crocodiles depend on the mangrove root systems and vegetated banks for nesting cover and basking sites; a forest transformed by mass inundation into a largely open tidal mudflat would be profoundly less suitable habitat. Dolphins depend on the complex channel network of the intact mangrove ecosystem, with its associated fish communities sustained by the organic productivity of the mangrove food web.

Both species are also affected by changes in the fish communities of the Sundarbans. The fish stocks of the Bay of Bengal and the tidal channels are the shared resource base for dolphins (as predators), crocodiles (as predators), local fishers (as their livelihood), and the broader ecosystem (as the foundation of the food web). Overfishing, which has substantially reduced fish abundance in the Sundarbans waterways, directly reduces food availability for dolphins and indirectly affects crocodile prey availability. Climate-driven shifts in fish species composition as temperatures and salinity levels change could alter the prey landscape for both predators in ways that are not yet fully understood.

https://thesundarbantour.com/dimerchor-beach-sundarbans-hidden/

Looking Forward — Hope, Science, and the Work of Coexistence

Conservation in the 21st Century

The conservation of crocodiles and dolphins in the Sundarbans requires confronting a paradox: the animals need both protection from human harm and the engagement of human communities in their defence. The fortress-conservation model — in which wildlife is protected by simply excluding people from critical habitat — has limited applicability in the Sundarbans, where millions of people depend on the same waterways that crocodiles and dolphins inhabit. Sustainable conservation must find ways to reduce the incidental mortality that human activities cause — the gillnet entanglements, the habitat disturbance, the pollution — without eliminating the livelihoods that human communities depend on.

Alternative fishing gear programmes that replace lethal monofilament gillnets with designs that allow dolphins to detect and avoid them — such as nets with acoustic pingers that emit sounds at frequencies dolphins can hear — have shown promise in other dolphin conservation contexts and deserve expansion in the Sundarbans. Community-based monitoring schemes, in which local fishers are trained and equipped to report dolphin and crocodile sightings and mortalities, create both a valuable data stream for conservation managers and a sense of ownership and engagement among communities that might otherwise view the animals purely as competition or hazard.

For crocodiles, the continued work of the Bhagabatpur Crocodile Project – expanded under a new ten-year management plan that aims to double the facility’s capacity – represents the most direct mechanism for maintaining and growing the Sundarbans population. The target of breeding more than 15 crocodiles per year and releasing them into wild Sundarbans rivers after three years of captive rearing continues the approach that has driven the species’ partial recovery since 1976. Combining this with improved habitat protection — particularly the management of the mangrove fringe zones where crocodile nesting occurs — gives the species its best chance.

For dolphins, the most urgent conservation priorities are reducing gillnet mortality and maintaining freshwater inflows to the Sundarbans. The first requires engagement with fishing communities and regulatory authorities to phase out the most dangerous gear types. The second requires a political and institutional commitment to the Sundarbans’ water needs that currently competes with powerful agricultural and urban demands for Ganges water upstream. India’s National Mission for Clean Ganga, which aims to restore the ecological flow of the Ganges, could, if successful, provide meaningful benefits for the Sundarbans’ freshwater-dependent wildlife — though the implementation of such large-scale hydrological restoration is enormously challenging.

A January 2026 announcement of a second range-wide estimation of both Ganges and Irrawaddy dolphin populations in the Sundarbans and Odisha – incorporating updated survey methodologies – represents the kind of renewed scientific commitment that is essential for informed management. Understanding where the animals are, how many there are, what their population structure looks like, and how their distribution is changing over time is the foundation on which all effective conservation rests.

The Wider Meaning: What These Species Tell Us

The saltwater crocodile and the river dolphins of the Sundarbans are not merely charismatic fauna to be preserved for their aesthetic or ecological value, though they are certainly both. They are, in a deeper sense, biological chronicles: the crocodile carrying in its unchanged body plan the genetic memory of 95 million years of evolutionary history and the Ganges River dolphin representing one of the last living remnants of an ancient cetacean lineage that once knew a very different world of rivers and coasts. To lose these animals would be to lose something irreplaceable from the library of life — not just a species but an evolutionary story, a biological lineage, a piece of the planet’s history.

In the Sundarbans, these ancient animals exist alongside millions of some of the world’s most vulnerable human beings — people who face the same climate-driven threats of storm surge and salinity and loss of livelihood as the wildlife around them. The fates of the crocodile, the dolphin, and the Sundarbans people are not separate narratives. They are one story, told in the same tidal waters, the same rising seas, the same struggle between the immense creative power of the natural world and the equally immense disruptive power of the human one.

The Sundarbans is a place of extraordinary resilience. Its ancient inhabitants – the crocodile watching from the mudflat and the dolphin turning invisible through the opaque channel water – have survived much. Whether they can survive the pace of change that now confronts them will depend on choices being made not just in the delta itself, but in the cities, parliaments, and boardrooms far upstream and far away.

Conclusion: Ancient Lives in an Imperilled World

The saltwater crocodile and the river dolphins of the Sundarbans share, across their profound biological differences, a single condition: they are survivors of worlds that no longer exist, adapted to environments that are now changing faster than the pace of evolutionary response. The crocodile’s body has barely changed since the Mesozoic; the Ganges River dolphin’s lineage diverged from the marine cetacean world tens of millions of years before the Sundarbans itself came into existence. They have outlasted ice ages, continental shifts, and the extinctions of countless species that once shared their world. What they have not outlasted, so far, is the combination of deliberate persecution, habitat destruction, and now climate-driven ecosystem change that defines the human era.

But the story is not yet finished. The crocodiles of the Bhagabatpur breeding pools, the dolphins patrolling the northeastern channels of the Bangladesh Sundarbans, the hatchlings of both species observed with cautious optimism in recent surveys — these are signs that the window of possibility remains open. Conservation effort, sustained and intelligent and politically backed, can and does make a difference. The recovery of the saltwater crocodile from the brink of extinction across much of its Indian range within living memory demonstrates what is possible when the will and the resources are applied.

The Sundarbans does not need us to save it from its ancient inhabitants. The crocodile and the dolphin belong there in ways that are older and more fundamental than any human claim. What the Sundarbans needs is for us to get out of the way in the right places, to reduce the harm we cause in others, and to make the political and economic choices upstream and globally that give this extraordinary living delta a future commensurate with its past.

https://whc.unesco.org/en/list/452/

Key References and Further Reading

• Aziz, M. A. & Islam, M. A. (2018). Population status and spatial distribution of saltwater crocodile in the Sundarbans of Bangladesh. Bangladesh Journal of Zoology, 46(1), 33-44.
• Greater Sundarbans (2024). Crocodiles in the Sundarbans. greatersundarbans.org.
• Greater Sundarbans (2024). Dolphins in the Sundarbans. greatersundarbans.org.
• India Crocodile Conservation Project (2024). 50th Anniversary Report. Padhai.ai.
• IUCN SSC Crocodile Specialist Group (2025). Crocodylus porosus assessment.
• Minton, A. G. et al. (2017). Orcaella brevirostris. IUCN Red List.
• Mondal, J. & Bandyopadhyay, J. (2017). Human-crocodile conflict in the Indian Sundarban. Oryx, 51(3).
• Sinha, R. K. & Kannan, K. (2014). Ganges River Dolphin: Biology, Ecology, and Conservation Status in India. Ambio, 43(8), 1029-1046.
• Smith, B. D., Braulik, G., Ahmed, B. & Mansur, R. (2006). Abundance of Irrawaddy dolphins and Ganges River dolphins in the Sundarbans mangrove forest of Bangladesh. Marine Mammal Science, 22, 527-547.
• Smith, B. D. et al. (2009). Habitat selection of freshwater-dependent cetaceans and potential effects of declining freshwater flows and sea-level rise in the Sundarbans. Aquatic Conservation, 19, 209-225.
• West Bengal Forest Department (2025). Sundarbans Biosphere Reserve Saltwater Crocodile Census.
• Whale and Dolphin Conservation (2024). Irrawaddy Dolphin Species Guide. uk.whales.org.
• Wildlife Conservation Society Bangladesh. Dolphin Conservation Programme Reports.
• Zero Carbon Analytics (2022). Loss and Damage in the Sundarbans.

This article was researched and written drawing on peer-reviewed literature, government survey data, and conservation organisation reports published through June 2026. Population figures represent the best available estimates at the time of writing. The Sundarbans ecosystem is under active scientific study, and figures may be updated as new surveys are completed.