55
Chapter three: Exercise energetics
whales (Globicephala macrorhynchus), named “the cheetahs of the deep sea,” can sustain
their unusual 9.0 m s −1 sprints chasing prey for only 20–80 s (Aguilar de Soto et al. 2008).
Together these changes in the amount of energy expended per meter moved result in
a characteristic U-shaped relationship between COT and swimming speed (Figure 3.3b).
Importantly, for each swimmer and species there is a minimum COT that defines the speed
or range of speeds that enable the animals to move the furthest for the least investment
of energy (Schmidt-Nielsen 1972). Equivalent to the miles per gallon (MPG) fuel economy
rating of automobiles, the minimum COT (COT MIN ) provides an index of the energetic
efficiency of marine mammals. From Figure 3.3b, it is obvious that COT MIN occurs in the
trough of the U-shaped curve that relates COT to swimming speed, and that it decreases
with body mass. Interestingly, for many of the marine mammals measured to date this
minimum occurs at approximately 1.5–2.5 m s −1 regardless of the size of the animal. Not
surprisingly, the preferred or routine speeds of many marine mammals fall within or near
this cost-efficient range of swimming speeds (see Chapter 1).
Like Resting Metabolic Rate, the minimum cost of transport for marine mammals varies predictably with body mass (Table 3.1) according to
COT
779 mass
n 6 species r
83
MIN
29
2
=
=
=
-
.
(
,
. )
.
0
0
(3.3)
where
COT MIN is the minimum cost of transport in J kg −1 m −1
body mass is in kg (Williams 1999)
Remarkably, this relationship is indistinguishable from that describing the total cost of
transport for running mammals and attests to the shared ancestral lineages of highly
active mammalian specialists. Terrestrial mammals, phocid seals, otariids, large and small
odontocetes, and an estimate for a mysticete, the gray whale (Eschrichtius robustus), follow
the same regression with a few notable exceptions (Figure 3.3c). Phocid seals tend to show
lower transport costs compared to other marine mammals, especially when diving. This
difference has been attributed to metabolic changes associated with the dive response as
well as to the energy savings associated with incorporation of extended periods of gliding
during deep dives (see Section 3.2.4). Conversely, sea otters demonstrate COT MIN levels that
are two or three times predicted for other similarly sized marine mammals, depending on
whether the otter is swimming submerged or on the water surface, respectively (Williams
1989). The inefficient paddling swimming style of sea otters and a surface swimming
position instigate these high costs, and demonstrate the challenges that ancestral marine
mammals must have encountered when transitioning from land to sea (Williams 1999).
3.2.3 Field metabolic rates
As might be expected, measuring the energetic costs of free-ranging marine mammals
that spend more than 90% of their lives submerged is challenging and has involved a wide
variety of methods (see Section 3.3). Because energy expenditure is related to the body size
for wild mammals (Nagy 2005), the field metabolic rate of marine mammals (FMR MM in kJ
day −1 ) can be estimated by using the equation:
FMR
3511 mass
n 1 species r
43
MM
45
2
=
=
=
0
0
0
.
(
,
. )
(3.4)
where body mass is in kg (Maresh 2014). Based on this equation developed from measurements of field energetic costs for marine mammals ranging in body mass from 27 kg sea
Chapter three: Exercise energetics
whales (Globicephala macrorhynchus), named “the cheetahs of the deep sea,” can sustain
their unusual 9.0 m s −1 sprints chasing prey for only 20–80 s (Aguilar de Soto et al. 2008).
Together these changes in the amount of energy expended per meter moved result in
a characteristic U-shaped relationship between COT and swimming speed (Figure 3.3b).
Importantly, for each swimmer and species there is a minimum COT that defines the speed
or range of speeds that enable the animals to move the furthest for the least investment
of energy (Schmidt-Nielsen 1972). Equivalent to the miles per gallon (MPG) fuel economy
rating of automobiles, the minimum COT (COT MIN ) provides an index of the energetic
efficiency of marine mammals. From Figure 3.3b, it is obvious that COT MIN occurs in the
trough of the U-shaped curve that relates COT to swimming speed, and that it decreases
with body mass. Interestingly, for many of the marine mammals measured to date this
minimum occurs at approximately 1.5–2.5 m s −1 regardless of the size of the animal. Not
surprisingly, the preferred or routine speeds of many marine mammals fall within or near
this cost-efficient range of swimming speeds (see Chapter 1).
Like Resting Metabolic Rate, the minimum cost of transport for marine mammals varies predictably with body mass (Table 3.1) according to
COT
779 mass
n 6 species r
83
MIN
29
2
=
=
=
-
.
(
,
. )
.
0
0
(3.3)
where
COT MIN is the minimum cost of transport in J kg −1 m −1
body mass is in kg (Williams 1999)
Remarkably, this relationship is indistinguishable from that describing the total cost of
transport for running mammals and attests to the shared ancestral lineages of highly
active mammalian specialists. Terrestrial mammals, phocid seals, otariids, large and small
odontocetes, and an estimate for a mysticete, the gray whale (Eschrichtius robustus), follow
the same regression with a few notable exceptions (Figure 3.3c). Phocid seals tend to show
lower transport costs compared to other marine mammals, especially when diving. This
difference has been attributed to metabolic changes associated with the dive response as
well as to the energy savings associated with incorporation of extended periods of gliding
during deep dives (see Section 3.2.4). Conversely, sea otters demonstrate COT MIN levels that
are two or three times predicted for other similarly sized marine mammals, depending on
whether the otter is swimming submerged or on the water surface, respectively (Williams
1989). The inefficient paddling swimming style of sea otters and a surface swimming
position instigate these high costs, and demonstrate the challenges that ancestral marine
mammals must have encountered when transitioning from land to sea (Williams 1999).
3.2.3 Field metabolic rates
As might be expected, measuring the energetic costs of free-ranging marine mammals
that spend more than 90% of their lives submerged is challenging and has involved a wide
variety of methods (see Section 3.3). Because energy expenditure is related to the body size
for wild mammals (Nagy 2005), the field metabolic rate of marine mammals (FMR MM in kJ
day −1 ) can be estimated by using the equation:
FMR
3511 mass
n 1 species r
43
MM
45
2
=
=
=
0
0
0
.
(
,
. )
(3.4)
where body mass is in kg (Maresh 2014). Based on this equation developed from measurements of field energetic costs for marine mammals ranging in body mass from 27 kg sea