17
Chapter one: Hydrodynamics
to maneuverability and agility compared to large animals because turn radius increases
directly with body mass (Howland 1974; Weihs and Webb 1984). Escape by small prey animals is possible as they are able to turn in smaller radii and with higher angular velocities
than the larger predators, such as marine mammals (Domenici 2001). However, marine
mammals hold an advantage in that their absolute swimming speed is substantially
greater than the speed of the prey.
Marine mammals exhibit divergent body designs that suggest differences in performance regarding stability and maneuverability. A body design adapted for stability when
swimming would aid in minimizing energy expenditure and increase propulsive efficiency. In addition, a stable body design would reduce transverse movements of the body
that could interfere with effective use of sensory systems. To understand how variation in
the morphology of animals can affect maneuverability, consideration should be given to
parameters associated with stability. Morphological characters that deviate from those of
a stable design (i.e., like an arrow) are expected to enhance maneuvering performance is
dependent on the location and design of control surfaces (i.e., flippers, fins, flukes) relative
to the center of gravity (CG), and rigidity of the body. Most analyses to date have been
performed on cetaceans and sea lions (Fish 2002; Fish et al. 2003) with comparisons to a
self-stabilizing design like an arrow (Harris 1936; Wegener 1991; Fish 2002). The arrow has
a rigid body, the CG is positioned anterior on the body, and control surfaces exhibiting
sweep and dihedral that are located far posterior of CG.
1.3.7 Maneuverability in cetaceans
The placement and design of control surfaces of cetaceans indicates a relatively stable (e.g.,
like an arrow) configuration (Fish 2002), although there are marked differences between
species. For example, the CG for the common dolphin Tursiops truncatus is located at a
position of 41% of body length (Fish 2002). Although this position appears to enhance
stability, it also appears to be nearly coincident with the center of buoyancy (Slijper 1979;
Weihs 1993; Fish 2002). As a result, delphinids can be unstable with respect to roll and
can side-swim, swim upside down, and barrel-roll (Layne and Caldwell 1964; Klima
et al. 1987). However, the dorsal fin, when present, is located approximately over the center of gravity and is immobile (Fish and Rohr 1999). This position limits the dorsal fin’s
effectiveness in developing a turning moment but allows the fin to prevent side-slip and
oppose rolling. Alternatively, the beluga whale, Delphinapterus leucas, which lacks a dorsal
fin, rolls during turns (Fish 2002).
The mobile control surfaces of cetaceans are located at a distance from the CG and
provide the major percentage of area for control (Slijper 1961; Aleyev 1977; Edel and Winn
1978; Fish and Battle 1995). The mobility of flippers in dolphins capable of rapid sprints
and fast cruising appears to be more constrained when compared to the flippers of slowswimming, highly maneuverable animals (Howell 1930; Pilleri et al. 1976; Klima et al.
1987). For example, the shoulder musculature of I. geoffrensis is highly differentiated in contrast to the faster swimming Lagenorhynchus albirostris, Phocoena phocoena, and T. truncatus
(Klima et al. 1987).
Flexibility in the body of cetaceans is generally constrained (Long et al. 1997). The
highly compressed cervical vertebrae and streamlined body form restrict bending in the
anterior region of the body, although some species have un-fused cervical vertebrae that
facilitate flexion of the neck (Ridgway and Harrison 1985; Narita and Kuratani 2005). Turns
are initiated anteriorly with lateral flexion of the head, and adduction and rotation of the
flippers into the turn (Fish 1997). When not actively fluking, there is substantial lateral
Chapter one: Hydrodynamics
to maneuverability and agility compared to large animals because turn radius increases
directly with body mass (Howland 1974; Weihs and Webb 1984). Escape by small prey animals is possible as they are able to turn in smaller radii and with higher angular velocities
than the larger predators, such as marine mammals (Domenici 2001). However, marine
mammals hold an advantage in that their absolute swimming speed is substantially
greater than the speed of the prey.
Marine mammals exhibit divergent body designs that suggest differences in performance regarding stability and maneuverability. A body design adapted for stability when
swimming would aid in minimizing energy expenditure and increase propulsive efficiency. In addition, a stable body design would reduce transverse movements of the body
that could interfere with effective use of sensory systems. To understand how variation in
the morphology of animals can affect maneuverability, consideration should be given to
parameters associated with stability. Morphological characters that deviate from those of
a stable design (i.e., like an arrow) are expected to enhance maneuvering performance is
dependent on the location and design of control surfaces (i.e., flippers, fins, flukes) relative
to the center of gravity (CG), and rigidity of the body. Most analyses to date have been
performed on cetaceans and sea lions (Fish 2002; Fish et al. 2003) with comparisons to a
self-stabilizing design like an arrow (Harris 1936; Wegener 1991; Fish 2002). The arrow has
a rigid body, the CG is positioned anterior on the body, and control surfaces exhibiting
sweep and dihedral that are located far posterior of CG.
1.3.7 Maneuverability in cetaceans
The placement and design of control surfaces of cetaceans indicates a relatively stable (e.g.,
like an arrow) configuration (Fish 2002), although there are marked differences between
species. For example, the CG for the common dolphin Tursiops truncatus is located at a
position of 41% of body length (Fish 2002). Although this position appears to enhance
stability, it also appears to be nearly coincident with the center of buoyancy (Slijper 1979;
Weihs 1993; Fish 2002). As a result, delphinids can be unstable with respect to roll and
can side-swim, swim upside down, and barrel-roll (Layne and Caldwell 1964; Klima
et al. 1987). However, the dorsal fin, when present, is located approximately over the center of gravity and is immobile (Fish and Rohr 1999). This position limits the dorsal fin’s
effectiveness in developing a turning moment but allows the fin to prevent side-slip and
oppose rolling. Alternatively, the beluga whale, Delphinapterus leucas, which lacks a dorsal
fin, rolls during turns (Fish 2002).
The mobile control surfaces of cetaceans are located at a distance from the CG and
provide the major percentage of area for control (Slijper 1961; Aleyev 1977; Edel and Winn
1978; Fish and Battle 1995). The mobility of flippers in dolphins capable of rapid sprints
and fast cruising appears to be more constrained when compared to the flippers of slowswimming, highly maneuverable animals (Howell 1930; Pilleri et al. 1976; Klima et al.
1987). For example, the shoulder musculature of I. geoffrensis is highly differentiated in contrast to the faster swimming Lagenorhynchus albirostris, Phocoena phocoena, and T. truncatus
(Klima et al. 1987).
Flexibility in the body of cetaceans is generally constrained (Long et al. 1997). The
highly compressed cervical vertebrae and streamlined body form restrict bending in the
anterior region of the body, although some species have un-fused cervical vertebrae that
facilitate flexion of the neck (Ridgway and Harrison 1985; Narita and Kuratani 2005). Turns
are initiated anteriorly with lateral flexion of the head, and adduction and rotation of the
flippers into the turn (Fish 1997). When not actively fluking, there is substantial lateral