LESSON 2 - SeaTrek Programs

Lesson 2
Behind the Bottlenose
To improve hydrodynamic efficiency, dolphins have a short, stiff neck positioned on a fusiform
(torpedo-shaped) body. This body shape helps dolphins to swim at high speeds, up to approximately 25
mph! Their front appendages are flipper-like fins and their hind appendages have disappeared. Dolphins
have a muscular tail to provide a powerful means of propulsion. Three sets of fins help bottlenose dolphins
swim. Moving up and down, the powerful tail flukes propel them through the water, the dorsal fin keeps them
upright and stable, and the pectoral fins allow them to steer. Bottlenose dolphins are fast swimmers, regularly
clocking in at 2-4 mph, however, they’ve been seen swimming as rapidly as 25 mph! They’re also
known to be able to hold their breath for seven or more minutes, but typically they surface to breathe one to
two times a minute.
Dorsal fin
Blowhole
Mouth/ rostrum
Tail flukes
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Pectoral flippers
Figure 2.3: Bottlenose dolphin anatomy
All of the external appendages are relatively small in proportion to the dolphins’ body bulk. To become
as streamlined as possible, what may once have been dolphin nostrils have moved to the top of their
head for easy breathing at the surface of the water. Even dolphin genitalia and mammary glands are
neatly situated within the body, rather than externally, to enhance the streamlining of the body!
Dolphins have sensory adaptations that are not externally visible. While dolphins do not have external
ears, they have unique ways of receiving
sounds through echolocation (see Figure 2.4). This
helps to make up for the fact that dolphins probably
do not have a sense of smell like many mammals.
The dolphins’ rostrum, or beak, is thick,
rounded, and short--usually about three inches
long. Their lower jaw extends beyond their upper
jaw, making it seem as though dolphins are always
smiling. They have 80-100 sharp, cone-shaped
teeth. If you could see the inner part of their teeth,
you would notice growth rings by which you could
tell their age--much like you can with the growth
rings in tree trunks!
Figure 2.4: To echolocate, dolphins produce sound in their larynx and nasal sacs
and focus the sounds through their melon. Sound waves will bounce off
objects in the dolphins’ path and are received back through the dolphins’
lower jawbone, where receptors send the information to the
brain for interpretation.
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