245
chapter eleven
Acoustics
Dorian Houser and Jason Mulsow
11.1 The big picture challenge and summary
Life as an aquatic mammal means exploiting an environment that is less conducive to the
transmission of light than it is to sound. Light energy is attenuated rapidly by sea water
such that in many oceans of the world little usable light exists beyond ~200 m depth. Even
above this point, termed the euphotic zone, light attenuation limits the distance over which
vision is useful, which is seldom more than tens of meters. On the other hand, the ocean is
a favorable environment for sound transmission. Sound travels faster in water (~1500 m/s)
than in air (~340 m/s) and is attenuated orders of magnitude less per unit of distance traveled. So, how does an animal whose ancestors were land-walking, primarily visual creatures adapt to an environment that is unfavorable to vision (see also Chapter 12)? Marine
mammals must forage for food (often mobile and elusive), find mates, navigate the oceans,
and avoid predators over scales where vision may be of limited use in the sea. To achieve
these goals, marine mammals need to be able to detect and identify sound, localize sound
sources, and project sound in an efficient manner, all within the constraints of the generalized mammalian bauplän.
Contents
11.1 The big picture challenge and summary ....................................................................... 245
11.2 Knowledge by order .......................................................................................................... 246
11.2.1 Order Cetacea ......................................................................................................... 246
11.2.1.1 Hearing ..................................................................................................... 246
11.2.1.2 Sound production ................................................................................... 251
11.2.2 Order Carnivora ..................................................................................................... 253
11.2.2.1 The Pinnipeds: Families Phocidae, Otariidae, and Odobenidae ..... 253
11.2.2.2 Family Mustelidae................................................................................... 256
11.2.2.3 Family Ursidae ........................................................................................ 257
11.2.3 Order Sirenia .......................................................................................................... 257
11.3 Responses to environmental noise .................................................................................. 258
11.4 Tools and methods ............................................................................................................. 259
11.5 Lingering mysteries ........................................................................................................... 261
References ..................................................................................................................................... 263
chapter eleven
Acoustics
Dorian Houser and Jason Mulsow
11.1 The big picture challenge and summary
Life as an aquatic mammal means exploiting an environment that is less conducive to the
transmission of light than it is to sound. Light energy is attenuated rapidly by sea water
such that in many oceans of the world little usable light exists beyond ~200 m depth. Even
above this point, termed the euphotic zone, light attenuation limits the distance over which
vision is useful, which is seldom more than tens of meters. On the other hand, the ocean is
a favorable environment for sound transmission. Sound travels faster in water (~1500 m/s)
than in air (~340 m/s) and is attenuated orders of magnitude less per unit of distance traveled. So, how does an animal whose ancestors were land-walking, primarily visual creatures adapt to an environment that is unfavorable to vision (see also Chapter 12)? Marine
mammals must forage for food (often mobile and elusive), find mates, navigate the oceans,
and avoid predators over scales where vision may be of limited use in the sea. To achieve
these goals, marine mammals need to be able to detect and identify sound, localize sound
sources, and project sound in an efficient manner, all within the constraints of the generalized mammalian bauplän.
Contents
11.1 The big picture challenge and summary ....................................................................... 245
11.2 Knowledge by order .......................................................................................................... 246
11.2.1 Order Cetacea ......................................................................................................... 246
11.2.1.1 Hearing ..................................................................................................... 246
11.2.1.2 Sound production ................................................................................... 251
11.2.2 Order Carnivora ..................................................................................................... 253
11.2.2.1 The Pinnipeds: Families Phocidae, Otariidae, and Odobenidae ..... 253
11.2.2.2 Family Mustelidae................................................................................... 256
11.2.2.3 Family Ursidae ........................................................................................ 257
11.2.3 Order Sirenia .......................................................................................................... 257
11.3 Responses to environmental noise .................................................................................. 258
11.4 Tools and methods ............................................................................................................. 259
11.5 Lingering mysteries ........................................................................................................... 261
References ..................................................................................................................................... 263