Unique and Endangered: Exploring the Fascinating World of River Dolphins ,The fact that freshwater whales in fact exist on our planet deserves much more fanfare – especially considering how their population is declining.
Many species of river dolphins, in particular, live in waterways spanning multiple continents and countries around the world. Their unique habitats correlate with strange qualities and unusual behaviors not found in harbor porpoises and other cetaceans.
But as the world’s great rivers change with human development, river dolphins appear to be paying a price.
The International Union for Conservation of Nature Red List now categorizes all river dolphin species as endangered or worse, with populations declining rapidly or disappearing entirely in recent years.
While these (mostly) freshwater mammals share many common characteristics and a common ancestor with oceanic dolphins, they are hardly new to the evolutionary tree.
Research shows that the river dolphin’s marine counterpart entered fresh water more than 5 million years ago.
This was probably during the Miocene epoch, when global sea levels were much higher than they are today. Species such as those in the Amazon and the Ganges now live exclusively in fresh water.
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River dolphin Characteristic
Compared to the more popular marine species of bottlenose dolphins or spinner dolphins, most river dolphins are immediately recognizable by unusual head and facial features that appear to have evolved for optimal survival in their habitats.
(Credit: Michel VIARD/Getty Images)
Located behind a prominent forehead, the eyes of these creatures are usually smaller and less effective. In fact, some populations are practically blind; as such, these species exhibit echolocation abilities (and a unique inner ear) unlike all other cetaceans.
Globally, other key features include a low triangular dorsal fin, broad and “fins with visible fingers” and a flexible neck, according to a 2020 study. in PNAS put it on
The latter characteristic allows them to turn their heads significantly, sometimes giving the appearance of a wrinkled double chin under the head.
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Freshwater dolphin Snout
Perhaps the most obvious and recognizable attribute of the river dolphin is its long and serrated beak-like snout.
(Credit: Shutterstock/Uwe Bergwitz)
This proboscis, along with its echolocation, probably serves as a hunting asset in the murky, muddy waterways that the dolphins inhabit.
The Amazon dolphin is also unique known to have molars among its more than 100 teeth that can help crush snails, turtles and other crustacean prey. This chewing differs from most dolphins, which use their teeth to grasp and trap food before swallowing it whole.
The myth of the Boto dolphins
Perhaps because of their novelty and strange characteristics, multiple cultures developed myths and legends around these freshwater whales.
Groups in Peru’s Amazon River basin have long believed that the river dolphin, or boto, can change shape into a seductive person and lures people to their deaths by drowning. One version of an encounter tells of a boto coming to a woman at night disguised as her husband; after intercourse the woman became pregnant and gave birth to a child.
Similarly, in China, the Yangtze River Dolphin is believed to be the reincarnation of a legendary princess who was drowned in the river after refusing to marry.
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Many South American species
More than half a dozen species of river dolphins have been identified worldwide. Growing up to 350 pounds and nearly 9 feet long, the Amazon’s pink dolphins are the largest and most widely recognized.
Similar species in South America include the Araguaian boto, named after a river that inhabits Brazil, and the Bolivian river dolphin.
The tuxedo, also found in the Amazon, most closely resembles a bottlenose dolphin (though smaller) and uniquely exhibits more playful and social qualities.
A smaller, gray-pale species called la plata or franciscana river dolphin is the only species that lives in salt water. It occupies the estuaries and coastal waters of Brazil, Uruguay and Argentina.
Reports over the past two decades show a rapid decline among most of these species, including some populations.”half each decade”, according to a Mongabay report.
Freshwater dolphins of Asia
Another well-established species in the Eastern Hemisphere calls the Ganges River home in parts of India, Bangladesh and Nepal.
These blind river dolphins, or susu, have completely lost their sight, perhaps due to the murky water, and possess exceptional echolocation abilities for hunting. A similar species, the Indus river dolphin of south-central Pakistan, is named one of the most endangered cetaceans in the world.
As of 2014 research in Ambio also revealed that populations of Gangetic susu have declined from an estimated 4,000 to 5,000 in the early 1980s to about 3,500.
In addition to the above groups, a pale blue-gray dolphin known as the baiji has also long inhabited the Yangtze River in China. But this species is now believed to be extinct.
The last confirmed sighting certificate occurred in 2002although unconfirmed claims of encounters with bottlenose dolphins still appear from time to time.
Read more: How do we know when a species is extinct?
Threats to species
Amid climate change with increasing human development and urbanization, a mix of several forces appears to be killing river dolphins.
A few of the best threats include hydroelectric development (with dams), pollution and water quality degradation, and fishing practices (such as bycatch).
To preserve these rare creatures nowadays, the World Wide Fund for Nature and other organizations have spearheaded various conservation efforts.
Advocates emphasize that best practices and solutions to protect river dolphins must be tailored to each unique population in the respective habitat and region it calls home.
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