Nov 052009
photo courtesy of Zemlinki! on Flickr Creative CommonsHomeAmazon River Basin
Habitatrivers and flooded forest
Nichelarge opportunistic predator
Favorite Foodfish
Lengthup to 9 feet
Weightup to 350 pounds
Status Vulnerable to Extinction
Threatsdam construction, pollution

The Amazon River is the world’s largest river by volume. Winding for thousands of miles across the interior of South America, this mighty river and its tributaries empty nearly 20% of the world’s freshwater into the Atlantic Ocean. Within the vast expanse of the river system live many bizarre creatures. But despite its reputation for eccentric natural splendor, few would have thought that the Amazon River is home to a dolphin.

The boto dolphin, also known as the Amazon river dolphin or pink dolphin, inhabits the murky depths of the Amazon, up to 1,800 miles inland from the sea. Among the dolphin family, the river dolphins are the most primitive. Most river dolphins have smaller brains than their marine counterparts, owing to their murkier habitat and mostly solitary nature. The boto dolphin has the largest brain of any of the river species, though it is still smaller than most marine species such as the bottlenose and common dolphin.

The boto is the largest of this family of rare freshwater dolphins, with adults reaching lengths of up to 8 feet. It is known and named for its pink color, which is believed to be caused by capillaries close to the skin. In older adults, the pink color will recede into a gray coloration.

Like all dolphins, the boto dolphin is a carnivore. It feeds on a plethora of underwater species of fish, turtles, and crabs, using its needle-like front teeth to grab slippery prey and its flattened back teeth to crush tough shells. It hunts for food on short dives of usually no more than a minute, using its long beak to rummage along the muddy bottom and among fallen trees for tasty morsels. Because of the lack of visibility in the murky water, the boto relies not on sight, but on sound to locate prey. Emitting a series of high-frequency clicks on each dive, the boto navigates by sonar and detects subtle vibrations through its lower jaw bone.

The range of the boto dolphin depends on the time of year and the condition of the river. In the rainy season, boto dolphins will venture into the flooded rainforest to explore their newly expanded feeding grounds. However, if they’re not careful, they can be stranded in ponds when the dry season arrives and tributaries shrink due to lack of rain. During the dry season, the animals mostly prefer deeper sections of the main channels.

Of all the river dolphins, the boto is faring best in the wild. However, increased development along the Amazon River Basin will surely pose new challenges to the boto dolphins living in the river. Dam construction and pollution pose the greatest threat to river dolphin populations and have all but obliterated wild populations in the Ganges and Yangtze Rivers in Asia. For now, the boto dolphin is still locally common in South America. But it’s only as safe as our commitment allows it to be.

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