47
chapter three
Exercise energetics
Terrie M. Williams and Jennifer L. Maresh
3.1 Introduction: The challenge of exercising while diving
The question of how cetaceans, pinnipeds, and other marine mammal groups exercise
while holding their breath has been debated by scientists for many decades (Castellini
et al. 1985; Butler 1988; Davis et al. 2004; Davis and Williams 2012). In the previous chapters, we found that the solution to this problem has involved external changes such as
body streamlining and efficient swimming styles to reduce energetic costs (Chapter 1), as
well as internal changes, most notably the enhancement of on-board oxygen stores to support aerobic processes while underwater (Chapter 2). Here, we examine how the efficient
use of those oxygen stores, termed energetics, enables marine mammals to breath-hold for
periods far beyond those of terrestrial mammals, and consequently allows this group of
mammals to dive to remarkable depths.
As air-breathing vertebrates, all marine mammals are obligated to periodically return
to the water surface to breathe. This interruption in aquatic activities, one of the most
important being foraging, is due to an evolutionary history that involved the r e-invasion
of the oceans by the terrestrial ancestors of cetaceans (Thewissen et al. 1994), pinnipeds
(Berta 2012), sea otters (Riedman and Estes 1990), and sirenians (Barnes et al. 1985). As
a result, the internal building blocks required for exercising while diving by ancestral
marine mammals included tolerance or modification of morphological, physiological,
biochemical, and molecular mechanisms originally intended for locomotion on land
(Williams 1999).
Contents
3.1 Introduction: The challenge of exercising while diving ................................................ 47
3.2 Energetic costs of marine mammals ................................................................................. 48
3.2.1 Resting metabolic rates and costs .......................................................................... 50
3.2.2 Metabolic costs of swimming and diving ............................................................ 52
3.2.3 Field metabolic rates ................................................................................................ 55
3.2.4 Behavioral strategies to reduce the energetic cost of swimming and diving .... 57
3.2.5 The high cost of foraging activities ....................................................................... 60
3.3 Toolbox .................................................................................................................................. 61
3.3.1 Measuring oxygen consumption ........................................................................... 61
3.3.2 Indirect methods for determining energetic costs.............................................. 62
3.3.3 Measuring field metabolic rates ............................................................................. 62
3.4 Unsolved mysteries and future directions .......................................................................63
References .......................................................................................................................................64
chapter three
Exercise energetics
Terrie M. Williams and Jennifer L. Maresh
3.1 Introduction: The challenge of exercising while diving
The question of how cetaceans, pinnipeds, and other marine mammal groups exercise
while holding their breath has been debated by scientists for many decades (Castellini
et al. 1985; Butler 1988; Davis et al. 2004; Davis and Williams 2012). In the previous chapters, we found that the solution to this problem has involved external changes such as
body streamlining and efficient swimming styles to reduce energetic costs (Chapter 1), as
well as internal changes, most notably the enhancement of on-board oxygen stores to support aerobic processes while underwater (Chapter 2). Here, we examine how the efficient
use of those oxygen stores, termed energetics, enables marine mammals to breath-hold for
periods far beyond those of terrestrial mammals, and consequently allows this group of
mammals to dive to remarkable depths.
As air-breathing vertebrates, all marine mammals are obligated to periodically return
to the water surface to breathe. This interruption in aquatic activities, one of the most
important being foraging, is due to an evolutionary history that involved the r e-invasion
of the oceans by the terrestrial ancestors of cetaceans (Thewissen et al. 1994), pinnipeds
(Berta 2012), sea otters (Riedman and Estes 1990), and sirenians (Barnes et al. 1985). As
a result, the internal building blocks required for exercising while diving by ancestral
marine mammals included tolerance or modification of morphological, physiological,
biochemical, and molecular mechanisms originally intended for locomotion on land
(Williams 1999).
Contents
3.1 Introduction: The challenge of exercising while diving ................................................ 47
3.2 Energetic costs of marine mammals ................................................................................. 48
3.2.1 Resting metabolic rates and costs .......................................................................... 50
3.2.2 Metabolic costs of swimming and diving ............................................................ 52
3.2.3 Field metabolic rates ................................................................................................ 55
3.2.4 Behavioral strategies to reduce the energetic cost of swimming and diving .... 57
3.2.5 The high cost of foraging activities ....................................................................... 60
3.3 Toolbox .................................................................................................................................. 61
3.3.1 Measuring oxygen consumption ........................................................................... 61
3.3.2 Indirect methods for determining energetic costs.............................................. 62
3.3.3 Measuring field metabolic rates ............................................................................. 62
3.4 Unsolved mysteries and future directions .......................................................................63
References .......................................................................................................................................64