1
Hearing in Whales and Dolphins:
An Overview
WHITLOW W.L. Au
1. Introduction
Whales and dolphins belong to the mammalian order Cetacea. They are
found in all the oceans and seas of the world, from the equator to the polar
seas. A few species even inhabit fresh water lakes and rivers. A list of the
80 species of cetaceans is conveniently presented in a table by Ridgway
(1997). Cetaceans vary considerably in size, from the very large blue whale
(BaLaenoptera muscuLus), which is the largest living mammal, to the very
small harbor porpoise (Phocoena phocoena) and Commerson's dolphin
(CephaLorhynchus commersonii), which are typically slightly over a meter
in length.
Cetaceans are subdivided into two suborders, Odontoceti and Mysticeti.
Odontocetes are the toothed whales and dolphins. The largest odontocete
is the sperm whale (Physeter catodon), followed by Baird's beaked whale
(Berardius bairdii) and the killer whale (Orcinus orca). Within the suborder Odontoceti there are four superfamilies: Platanistoidea, Delphinoidea,
Ziphioidea, and Physeteroidea. Over half of all cetaceans belong to the
superfamily Delphinoidea, consisting of seven species of medium whales
and 35 species of small whales also known as dolphins and porpoises
(Ridgway 1997). Dolphins generally have a sickle-shaped dorsal fin, conical
teeth, and a long rostrum. Porpoises have a more triangular dorsal fin,
more spade-shaped teeth, and a much shorter rostrum (Ridgway 1997).
In many ways, the rostrums of porpoises resemble the lips of many terrestrial animals.
Mysticetes are "toothless," and in place of teeth they have rigid brushlike whalebone plate material called baleen hanging from their upper jaw.
The baleen are used to strain shrimp, krill, and zooplankton. All the great
whales are mysticetes or baleen whales and all, with the exception of the
Minke whale (BaLaenoptera acutorostrata), are larger than all species of
odontocetes. The sperm and Baird's beaked whales are the only odontocetes larger than Minke whales. Baleen whales are subdivided into four
families (see Table 1.1), BaLaenidae (right and bowhead whale), Eschrichti1
Hearing in Whales and Dolphins:
An Overview
WHITLOW W.L. Au
1. Introduction
Whales and dolphins belong to the mammalian order Cetacea. They are
found in all the oceans and seas of the world, from the equator to the polar
seas. A few species even inhabit fresh water lakes and rivers. A list of the
80 species of cetaceans is conveniently presented in a table by Ridgway
(1997). Cetaceans vary considerably in size, from the very large blue whale
(BaLaenoptera muscuLus), which is the largest living mammal, to the very
small harbor porpoise (Phocoena phocoena) and Commerson's dolphin
(CephaLorhynchus commersonii), which are typically slightly over a meter
in length.
Cetaceans are subdivided into two suborders, Odontoceti and Mysticeti.
Odontocetes are the toothed whales and dolphins. The largest odontocete
is the sperm whale (Physeter catodon), followed by Baird's beaked whale
(Berardius bairdii) and the killer whale (Orcinus orca). Within the suborder Odontoceti there are four superfamilies: Platanistoidea, Delphinoidea,
Ziphioidea, and Physeteroidea. Over half of all cetaceans belong to the
superfamily Delphinoidea, consisting of seven species of medium whales
and 35 species of small whales also known as dolphins and porpoises
(Ridgway 1997). Dolphins generally have a sickle-shaped dorsal fin, conical
teeth, and a long rostrum. Porpoises have a more triangular dorsal fin,
more spade-shaped teeth, and a much shorter rostrum (Ridgway 1997).
In many ways, the rostrums of porpoises resemble the lips of many terrestrial animals.
Mysticetes are "toothless," and in place of teeth they have rigid brushlike whalebone plate material called baleen hanging from their upper jaw.
The baleen are used to strain shrimp, krill, and zooplankton. All the great
whales are mysticetes or baleen whales and all, with the exception of the
Minke whale (BaLaenoptera acutorostrata), are larger than all species of
odontocetes. The sperm and Baird's beaked whales are the only odontocetes larger than Minke whales. Baleen whales are subdivided into four
families (see Table 1.1), BaLaenidae (right and bowhead whale), Eschrichti1