Environmental Engineering Reference
In-Depth Information
Comprehensive comparisons (Schmidt-Nielsen 1972;
Tucker 1975) showed that swimming is the least
energy-demanding form of animal locomotion; flying
comes next, and running (by ectotherms or endotherms)
is the most expensive. T. M. Williams (1999) offered a
more nuanced appraisal, confirming that submerged fish
swimming is by far the most energy-efficient way of ani-
mal locomotion, followed by bird and bat flight. But the
submerged swimming of marine mammals has an energy
cost comparable to, or even higher than, mammalian
running; phylogenetic history, rather than mode of loco-
motion, determines the cost of transport in mammals.
The most expensive mode of transport is the surface
swimming of vertebrates ranging from ducks to humans
(fig. 4.5).
All transport modes are limited by metabolic scopes,
the ratios between peak metabolism and RMR or BMR.
For running mammals the scopes are typically about 10
times RMR, for horses 20, and for coyotes, wolves, and
dogs 31-32. For birds the scopes do not appear to go
beyond 20 (but they start from higher specific BMRs),
and 15 is a short-term scope in some fish. Reptilian and
amphibian scopes are just 5-10, posing a severe limita-
tion on the activity of these heterotrophs (Huey, Pianka,
and Schoener 1983). Whereas the top aerobic power in
small birds and rodents is, respectively, about 150 mW/
g and 50 mW/g, it is less than 9 mW/g in toads and 3
mW/g in iguanas. Rapid reptile motion depends on
short, anaerobically energized bursts that require subse-
quent long periods of recovery. In contrast, flying insects
put out 0.12-0.58 W/g, or up to 100 times their RMRs
(moths can go up to 150 times).
COT scales allometrically with body mass, with ex-
ponents for different modes of locomotion clustering
around
0.3. Such large submerged marine swimmers
as killer whales (2.5-5 t, 2-3 m/s) thus need less than 1
J/kg
m, and the best available rate for a 15-t grey whale
is just 0.4 J/kg
m (if the exponent holds, a baleen whale
would need
<
0.1 J/kg
m). In contrast, COT in mam-
malian surface swimmers (minks, muskrats, people) is
at least 10 and up to 40 J/kg
m (fig. 4.5) (Williams
1999). Because the mechanical power of swimming goes
up with the cube of velocity
ð
v
3
Þ
, the total energy de-
mand for swimming is a sum of RMR
ð
R) and v
3
(modi-
fied by a constant, k). The energy required per unit
distance is
ð
R
þ
kv
3
Þ
=
v, and its minimum value is when
v
¼ð
R
=
2k
Þ
0
:
33
, which means that a high RMR goes
with a high optimum speed and hence with high cost of
transport (Alexander 1999b).
Surface swimming is so costly because of the elevated
body drag (four to five times that of submerged swim-
ming) and the necessity of pushing a bow wave; that is
why more streamlined creatures (penguins) are more effi-
cient surface swimmers than sea otters or people. Sub-
merged swimming needs little or no energy to support
the neutrally buoyant fish, and the effort is overwhelm-
ingly channeled into overcoming the drag of the rela-
tively dense medium (Videler 1993). There are three
basic swimming modes: anguilliform propulsion of eels
and blennies, which uses whole-body undulation; caran-
giiform motion of most species, which confines the un-
dulation to the rear half or third of the body, often
aided by lunate tails; and the mainly pectoral swimming
of wrasses, parrot fish, and anglerfish.
Fish cruise by using alternate contractions of their aer-
obic muscles, which run the length of the body in a small
red band just under the skin; massive white (anaerobic)
muscles are used only for rapid, evasive bursts (fig. 4.5).
But such powerful swimmers as tuna and lamnid sharks
(makos and white) are distinguished not only by having
