Amazon river dolphin: Inia geoffrensis

Abstract

This chapter explores the Amazon River dolphin commonly known as boto. It belongs to the family Iniidae. The genus Inia is currently considered monospecific, with three recognized subspecies: Inia geoffrensis geoffrensis, I. g. boliviensis, and I. g. humboldtiana. The boto is the largest of the river dolphins with a maximum recorded body length of 255 cm and body mass of 207 kg for males and 225 cm and approximately 153 kg for females. It is also the most sexually dimorphic of the river dolphins, with males 16% longer and 55% heavier than females. The body is corpulent and heavy but extremely flexible. Nonfused cervical vertebrae allow movements of the head in all directions. The flukes are broad and triangular; the dorsal fin is long, low, and keel-shaped, extending from the mid-body to the strong, laterally flattened caudal peduncle. The flippers are large, broad, and paddle-like and are capable of separate circular movements. Although most of these characteristics restrict speed during swimming, they allow this dolphin to swim backward and to maneuver between trees and submerged vegetation to search for food in the flooded forest. The boto is mostly solitary and is not commonly seen in cohesive groups. Group size is generally from one to four individuals. Most groups of two are mother-calf pairs, but mixed groups and groups of males are also common. © 2009 Copyright © 2009 Elsevier Inc. All rights reserved.