Among the aquatic mammals in this part of the Amazon basin
, there are only two species of Cetaceans—the pink river dolphin and the gray dolphin.
The pink river dolphin, locally known as “bufeo
” or “boto” is the largest one in size (7–8 feet long); it also has the largest distribution. These dolphins feed on crabs, turtles and several species of fish, including piranhas, along
the murky looking “white-water” rivers and their black water tributaries. Pink river dolphins are also able to navigate through the forest and maneuver with their specially adapted necks, which can be moved sideways. They have a unique profile with a very narrow and long snout and a “blunt” dorsal fin that can seldom be seen when the individuals surface to breathe. The pinkish coloration is a result of the blood vessels located along the body and increases with age. Pink river dolphins are almost blind, but their extremely developed sonar compensates for this reduced sight.
The second species, the gray dolphin or “Tucuxi,” is 5 feet long, and their shape resembles a marine dolphin more than their same order neighbors. Gray dolphins have a grayish coloration, a shorter snout, and a more triangular dorsal fin. They also are apparently more active and breach more often.
River dolphins can be found in larger groups, sometimes along the deeper waters of larger rivers and can even be found along the south Atlantic coast of South America