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Evolution
Dolphins vs. Whales & Porpoises
The Ocean Environment
External Features
Ventral Features & Male Vs. Female
Fin Structure & Function
Senses
Brain & Intelligence
Thermo-regulation
Melon
Blowhole & Breathing
Vocalization
Echolocation
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Counter-shading
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Mother & Calf
Jumping & Synchronous Behavior
Behavior In The Water
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FIN STRUCTURE & FUNCTION

Identifying individual dolphins is difficult because animals in the ocean appear at the surface and then disappear rapidly beneath the water. A technique to identify wild dolphins, called JIZZ, is used. It classifies the dolphin's dorsal fin shape, location along the length of the animal's body, trailing edge notches, dive sequences, and fluke shape. But what are these fins and how do they function?

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Dorsal Fin

The dolphin body typically has five fins (some dolphins have only a small dorsal ridge while others, such as the "killer whale" have a very large dorsal fin). The dorsal fin, located on the top (dorsal side) of the animal, is filled with a fibrous  connective tissue. It serves to keep the animal upright (similar to a ship’s keel) and prevents "roll". Also it has a thermo-regulation (body temperature adjustment) function. As the dolphin is warm-blooded it must maintain a body temperature of 97-99 degrees F. Should the animal become overheated, the dorsal fin serves to release excess body heat to the environment. Blood vessels are generally not close to the surface of the dolphin's skin, except in the case of the pectoral and dorsal fins and the flukes. These are the specialized areas where thermo-regulation takes place. The dolphin's metabolic rate tends to be higher than land mammals, allowing it to survive in colder waters. Long times between breaths may also help in preventing the loss of body heat as cold air comes in contact with the blood stream in the lungs less frequently this way. Recent research at the University of California Santa Cruz has shown that calves require up to three years to develop the full thermo-regulatory function of their dorsal fin and flukes. This inability to fully thermo-regulate in the first years of life may help to explain the tendency of dolphins to give birth in warmer waters and in the warmer summer months. This fin, as it is one of the first body parts of the animal to be visible as the dolphin surfaces, serves as an identification “fingerprint” of each particular animal. Its unique shape and notch pattern on its trailing edge helps in this regard. Dolphin researchers photograph the dorsal fins of animals they are studying and maintain large libraries of such photographs. The backward curved shape of the Atlantic Bottlenose Dolphin's dorsal fin is termed “falcate”.

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If you compare the trailing edge of this dolphin's dorsal fin with the previous photograph of a dolphin's dorsal fin, it is obvious how identifications may be made by simply viewing the fin as it surfaces.
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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Flukes

The flukes are located on the end of the peduncle and are responsible for the propulsion (forward movement) of the animal. The tips of each fluke change position (up or down) as the flukes move the animal forward. Upward positioning of the tips provides a cup-like surface on which to catch more water during the upstroke. The flukes are connected to sets of very powerful muscle groups in the back and along the belly of the animal. The flukes represent two fins, as they are divided by a “median arch”. Like the dorsal fin, they are filled with fibrous connective tissue and function as thermoregulators. Flukes measure about 23 inches across in the adult dolphin, spreading about 20% of the animal’s total body length.

 

 

 

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Pectoral Fins

The remaining two fins are called the pectorals. Pectorals help the dolphin to stop and turn, acting as balancing planes. Pectorals are not involved in propulsion, as are the flukes. They are the only dolphin fins to contain bones. An x-ray of the dolphin's pectoral fins reveals bones similar to those found in the human arm, wrist and hand. The presence of such bones in the animal’s pectoral fins is evidence that the dolphin was once a land animal with frontal appendages which aided in its forward movement and support of its heavy body weight. It is believed the dolphin lived on land in India and Asia some 65 million years ago, at around the time of the dinosaur’s extinction. It has since left the land for a life in water, where it remains today (see the "Dolphin Evolution" section in this site). The dolphin uses its pectoral fins to help conserve body heat by adjusting blood circulation to them under varying water conditions. Adult pectoral fins measure from 11-19 inches and are curved back with a pointed tip.

 

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Peduncle
 
The peduncle is the muscular tail section located between the dorsal fin and the flukes. The muscles in the dorsal (upper) part of the peduncle are stronger than those located in the ventral (lower) part. The strong dorsal muscles provide the upward power stroke for the dolphin's forward motion as well as for its jumps. The weaker ventral muscles return the flukes to the downward position in readiness to provide the next upstroke.
 
 
 
 
 
 
 
 

Site Content
 
Understanddolphins.com contains information condensed from a number of reputable technical sources, peer reviewed journal articles, and respected dolphin research facilities, as well as from my personal experiences and observations as a dolphin VIP Tour Guide and Educator.
 
I have made every attempt to support the information presented in this site with video and still photographic images. On a regular basis I plan to produce more of these images and will continue to update the site with these as well as with any new and scientifically verified information which becomes available.

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