19
Chapter one: Hydrodynamics
permits dynamic production of lift that can induce torques around CG to promote instabilities. The location of the pectoral flippers close to CG would not produce large torques
and would be less effective in rapidly inducing turns. However, the pectoral flippers are
used for propulsion (Feldkamp 1987a,b), and propulsors arranged around CG are postulated to promote maneuverability (Webb et al. 1996). The highly flexible body of Zalophus
also enhances maneuverability. Bending of the body and neck is an integral component
of turning in conjunction with the flippers of pinnipeds (Godfrey 1985; Fish et al. 2011).
Dorsal bending of the spine allows the body to curve smoothly, maintaining a streamlined
appearance throughout the turn.
Zalophus generally can turn in small radii and at faster rates than cetaceans of similar
size. Minimum turn radii are 0.09–0.16 body lengths (Fish 2002; Fish et al. 2011). The maximum turning rate of Zalophus is 690°/s and the maximum centripetal acceleration is 5.13 g.
Such performance is superior to turning rates for cetaceans.
1.3.9 Energy capture from the external environment
As the energy cost of swimming can be large in the marine environment, marine
m ammals have adopted a variety of behavioral, morphological, and physiological
m echanisms to swim economically. Such mechanisms rely upon energy management
by capturing energy from external and internal sources. External sources of energy can
be utilized from the prevailing physics of the environment (i.e., gravity, hydrodynamics,
waves). In contrast, kinetic energy from muscular contraction that would typically be
lost can be recycled internally from the elastic properties of the connective tissues of the
body (Pabst 1996). In both cases, the available energy to perform the work of swimming
is augmented or conserved to lower metabolic power consumption, increase dive time,
and increase speed.
The capture of external forms of energy to add to the total energy budget for movement by marine mammals is known as free-riding. The simplest type of free-riding behavior is gliding while diving. The density of the body increases with depth due to increased
hydrostatic pressure. When diving deeply (>20 m), lung collapse reduces the net buoyant force causing the animal to sink (Ridgway et al. 1969; Ridgway and Howard 1979;
Kooyman and Ponganis 1998; Moore et al. 2011). The animal can glide deeper as gravity now supplies the motile force. The gliding configuration of the body minimizes drag
and reduces the metabolic cost of swimming. Whales, dolphins, and seals intermittently
switch between active swimming and gliding depending on the dive depth and the net
buoyancy of the body (Williams et al. 2000; Williams 2001). Exhalation before diving by
pinnipeds has been considered a mechanism to prevent decompression sickness, however,
this behavior may effectively reduce buoyancy to decrease the energy cost of swimming
during the initial descent (Kooyman 1973). During deep dives, dolphins can reduce energy
costs by approximately 20% when transiting to the bottom by using intermittent swimming behaviors (Williams et al. 1996; Williams 2001). During ascent, the reverse occurs
and the animal accelerates by actively swimming until its lungs re-inflate sufficiently to
provide positive buoyancy (Skrovan et al. 1999).
The occurrence of highly organized formations by cetaceans has been suggested as
an adaptation for energy economy (Kelly 1959). Formation swimmers are able to capture
energy from the vortex patterns in the wakes of conspecifics and decrease drag with a
concomitant decrease in overall energy cost of locomotion (Weihs 1973). In addition, when
two bodies are in close proximity, the water flow between them is accelerated resulting in
an attractive force due to the Bernoulli effect (Kelly 1959; Fish et al. 2013).
Chapter one: Hydrodynamics
permits dynamic production of lift that can induce torques around CG to promote instabilities. The location of the pectoral flippers close to CG would not produce large torques
and would be less effective in rapidly inducing turns. However, the pectoral flippers are
used for propulsion (Feldkamp 1987a,b), and propulsors arranged around CG are postulated to promote maneuverability (Webb et al. 1996). The highly flexible body of Zalophus
also enhances maneuverability. Bending of the body and neck is an integral component
of turning in conjunction with the flippers of pinnipeds (Godfrey 1985; Fish et al. 2011).
Dorsal bending of the spine allows the body to curve smoothly, maintaining a streamlined
appearance throughout the turn.
Zalophus generally can turn in small radii and at faster rates than cetaceans of similar
size. Minimum turn radii are 0.09–0.16 body lengths (Fish 2002; Fish et al. 2011). The maximum turning rate of Zalophus is 690°/s and the maximum centripetal acceleration is 5.13 g.
Such performance is superior to turning rates for cetaceans.
1.3.9 Energy capture from the external environment
As the energy cost of swimming can be large in the marine environment, marine
m ammals have adopted a variety of behavioral, morphological, and physiological
m echanisms to swim economically. Such mechanisms rely upon energy management
by capturing energy from external and internal sources. External sources of energy can
be utilized from the prevailing physics of the environment (i.e., gravity, hydrodynamics,
waves). In contrast, kinetic energy from muscular contraction that would typically be
lost can be recycled internally from the elastic properties of the connective tissues of the
body (Pabst 1996). In both cases, the available energy to perform the work of swimming
is augmented or conserved to lower metabolic power consumption, increase dive time,
and increase speed.
The capture of external forms of energy to add to the total energy budget for movement by marine mammals is known as free-riding. The simplest type of free-riding behavior is gliding while diving. The density of the body increases with depth due to increased
hydrostatic pressure. When diving deeply (>20 m), lung collapse reduces the net buoyant force causing the animal to sink (Ridgway et al. 1969; Ridgway and Howard 1979;
Kooyman and Ponganis 1998; Moore et al. 2011). The animal can glide deeper as gravity now supplies the motile force. The gliding configuration of the body minimizes drag
and reduces the metabolic cost of swimming. Whales, dolphins, and seals intermittently
switch between active swimming and gliding depending on the dive depth and the net
buoyancy of the body (Williams et al. 2000; Williams 2001). Exhalation before diving by
pinnipeds has been considered a mechanism to prevent decompression sickness, however,
this behavior may effectively reduce buoyancy to decrease the energy cost of swimming
during the initial descent (Kooyman 1973). During deep dives, dolphins can reduce energy
costs by approximately 20% when transiting to the bottom by using intermittent swimming behaviors (Williams et al. 1996; Williams 2001). During ascent, the reverse occurs
and the animal accelerates by actively swimming until its lungs re-inflate sufficiently to
provide positive buoyancy (Skrovan et al. 1999).
The occurrence of highly organized formations by cetaceans has been suggested as
an adaptation for energy economy (Kelly 1959). Formation swimmers are able to capture
energy from the vortex patterns in the wakes of conspecifics and decrease drag with a
concomitant decrease in overall energy cost of locomotion (Weihs 1973). In addition, when
two bodies are in close proximity, the water flow between them is accelerated resulting in
an attractive force due to the Bernoulli effect (Kelly 1959; Fish et al. 2013).