The idea of a freshwater dolphin can seem incredibly far-fetched, especially in temperate continents like North America and Europe. You might be surprised to find that these creatures continue to exist in some of the most complex and historically rich rivers of the world. Elusive, mysterious, and now incredibly rare, all of them are classified as ‘endangered’ or ‘critically endangered’. Unless their increasingly fragile habitats are conserved and protected, they may, unfortunately, become extinct within our lifetimes.
Thanks to projects like WWF’s River Dolphins Initiative, the main threats to river dolphins have been evaluated and are drawing more attention. With the help of global stakeholders, there is hope that remaining populations of freshwater cetaceans can be prevented from declining further. Threats like unsustainable fishing, infrastructure development, agriculture, and mining need to be contained – and in as timely a manner as possible.
Protected, clean, and continuous freshwater systems are key to increasing the chances of river dolphin survival in South America, South Asia, and Indochina. The species listed below are important bioindicators of their native habitats. The recovery of their highly evolved populations and the expansion of their distribution would hint at a healing environment.
1) Amazon river dolphin (Inia geoffrensis)
Also known as the pink river dolphin due to the prominently pinkish hues of its adult males, I. geoffrensis is truly breathtaking to behold. Anyone who is lucky enough to spot one of these charming mammals can count themselves extremely lucky. This endangered species has a fairly vast range, however, with some of its subpopulations found in Bolivia, Ecuador, Peru, Venezuela, Colombia, and Brazil. It occupies the Madeira, Orinoco, and Amazon River systems, which are associated with some of the most diverse wetland environments in the world.
Locally referred to as “boto” or “bufeo”, the Amazon river dolphin can measure as long as 8.2 feet (2.5 meters) and weigh as much as 400 pounds (181 kg)! Sexually dimorphic, the pinkish males are notably larger than the largest females. Their melon-shaped heads allow them to echolocate in murky rivers, where they cannot rely on visual cues to find suitable prey.
Like marine dolphins, Amazon river dolphins use whistling noises and clicks to communicate. Though they do travel in pods, they are often seen on their own or in pairs. Easily identified due to their lengthy, toothed snouts, they prefer to venture out in search of food during twilight. Small fish, freshwater turtles, and river crabs are some of their favorite treats.
2) Indus river dolphin (Platanista minor)
The Indus river dolphin has the characteristic pointed nose shared by most species of extant freshwater cetaceans. It grows much larger than the average human, with a maximum recorded length of about 8.5 feet (2.6 meters). Unlike the Amazon river dolphin, where the males are distinctly larger, this species tends to have longer females. This is largely due to the continued growth of the rostrum in sexually mature females – when fully grown, they have rostrums that are about 8 inches (20 cm) longer than those of males.
One of the most interesting developments in this species’ evolution is its loss of a crystalline eye lens. Technically, Indus river dolphins are blind. They rely almost solely on their echolocation skills to navigate through a small section of the Indus River system’s main stem. Though they were once widely distributed, these dolphins prefer to hunt within a stretch covering just 429 miles (690 km) of flowing water.
Classified as an endangered species on IUCN’s Red List, the Indus river dolphin has been severely affected by anthropogenic disturbances. It is estimated that there are less than 2,000 surviving individuals of this species. Overfishing, net entanglements, deforestation, and habitat degradation are just a few of the most severe threats to its survival.
3) Ganges river dolphin (Platanista gangetica)
Once grouped under the same species as the Indus river dolphin, P. gangetica was eventually considered its own taxon when genetic data, skull structure, and divergence trends revealed significant differences. It’s likely that the earliest populations of the Ganges river dolphin split from those of the Indus river dolphin in the Pleistocene epoch (i.e. 500,000+ years ago).
Nowadays, this dolphin is found only in the river systems of Nepal, northeastern India, and Bangladesh. It seems to be partial to conditions in deep, murky pools, river bends, and eddies. Despite the presence of markedly tiny eyes, it is believed to be functionally blind. It’s likely that the remnants of an optic nerve and retina can detect light but are unable to form decipherable images.
Slightly more abundant than the Indus river dolphin, this species is estimated to have about 5,000 surviving individuals. The majority of them are found in the Ganges River (India) and Brahmaputra River (Bangladesh). The construction of barrages and dams has isolated some populations and imposed challenges upon their access to migratory prey.
4) Irrawaddy river dolphin (Orcaella brevirostris)
Unlike the species listed above, the Irrawaddy dolphin is a euryhaline whale that can thrive in both marine and freshwater environments. Its subpopulations are generously scattered throughout the coastlines of South and Southeast Asia. Though it does enter marine environments, its estuarine populations tend to be geographically isolated. In India and Thailand, some small groups are fairly landlocked.
A critically endangered species with less than 300 surviving individuals, the Irrawaddy dolphin is set apart by its small dorsal fin, well-rounded forehead, and paddle-like flippers. As it does not have a pointed rostrum, its morphology is quite similar to that of the beluga whale. Bluish-grey in color, it has a couple of features that set it apart from virtually any other dolphin. These include the forward orientation of its blowhole and the anatomy of its jaws.
Slow-moving and shy, this unique cetacean travels in small pods. Though it is able to dive for up to 12 minutes at a time in coastal areas, it may struggle to compete with more specialized marine dolphins. Coupled with its non-aggressive nature, this may be one of the major reasons for its general restriction to inland waters.
5) Tucuxi (Sotalia fluviatilis)
Compared to the Amazon river dolphin, with which it shares a portion of its natural distribution, the “tucuxi” or “bufeo gris” is smaller and more playful. Although it is confined to riverine environments, it is morphologically more similar to oceanic dolphins than to its freshwater counterparts. In fact, it looks like a smaller version of the bottlenose dolphin. Bluish-grey, it may occasionally sport a rosy hue – possibly due to a heightened blood flow.
Data pertaining to population estimates and the exact distribution of tucuxi remain to be inconclusive. Nonetheless, this freshwater dolphin must face the same threats as many other endangered species within its native range. Spotted in Colombia, Ecuador, Peru, Venezuela, and Brazil, its foraging groups may occasionally be found chasing schools of fish.
In the western regions of Brazil, the tucuxi tends to be threatened by commercial fishing. As it interacts with economically important schools of freshwater fish, it is prone to becoming entangled in nets and getting caught as bycatch. Anthropogenic activities, such as the construction of dams, also harm local populations by instigating their fragmentation.
6) Yangtze finless porpoise (Neophocaena asiaeorientalis)
As suggested by its common name, the Yangtze finless porpoise is endemic to China’s Yangtze River. Known in Mandarin as “jiangtun”, this member of the Phocoenidae family is now classified as an endangered species. Pollution, illegal fishing, and other anthropogenic disturbances have severely reduced its populations and continue to threaten extant individuals. These toothed whales are now the sole surviving freshwater cetaceans of East Asia.
One of the most apparent traits of the finless porpoise is, of course, its lack of a dorsal fin. In place of one, it simply has a dorsal “groove” with slightly raised tubercles. Recent research has suggested that these tubercles may function as sensory organs to aid in this species’ calculated movements through freshwater. Other finless porpoises, including those that inhabit oceanic environments, share this trait as well.
Found in the main stem of the Yangtze River as well as some of its connected lakes, estuaries, swamps, and bays, this porpoise favors mild to warm temperatures. Elusive, it rarely approaches the water’s surface when humans are around. If you’re extra lucky, however, you may spot one leaping above river confluences during particularly agreeable days.
7) Chinese river dolphin (Lipotes vexillifer)
The Chinese river dolphin has recently been declared “critically endangered and possibly extinct” in the wild. A harsh warning for the fate of other dolphins if conservation plans are not put into practice, its decline highlights one of the worst possible outcomes of anthropogenic disturbances. The local fishing industry played a major role in this species’ demise. For decades, many individuals were caught in hooks and fishing gear. Electric fishing, which is illegal in China, also factored into its irreversible decline.
Locally known as “baiji”, the Chinese river dolphin was a member of the Lipotidae family. Distantly related to all extant dolphin species, it would rely on its built-in sonar system to navigate through turbid waters and to communicate with its conspecifics. Its females, which would become larger than males, would measure around 8 – 9 feet (2.4 – 2.7 meters) long at maturity. Clearly, given their sheer size and their carnivorous nature, they were apex predators.
Compared to other freshwater dolphins, this species would perform relatively short dives. As these would last for only 10 – 20 seconds, they were known for hunting in shallow areas. Despite their tendency to congregate close to the water’s surface and in large eddies, much of their behavior was – and will sadly always be – a mystery to local conservationists and researchers.
