This topic submitted by Alexandria Greenler (
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A beautiful sunset over Grahams Harbor, San Salvador, Bahamas. See other
from the Bahamas.
The mystic mammal has intrigued people for centuries. Dolphins and their relative, whales, arose fifty million years ago from primitive mammals that ventured into the seas. (Sea World,2002) Ancient Greeks believed that the dolphin is the sacred god Apollo. Because of the importance in Greek and Roman mythology, dolphins were used in their decorations for coins, pottery, and walls. (Encyclopedia,1994) Dolphins are still of importance today and the bottlenose dolphins are the most common of the eighty species of dolphins. Dolphins are classified in class Mammalia, order Cetacea and family Delphinidae The order Cetacea is divided further into three suborders Odontecti, Mysticeti, and Archaeoceti. The bottlenose dolphin and it’s relatives are classified into the suborder Odontecti because they are toothed whales. The family Delphinidae includes about thirty species. The genus is Tursiops and the species of the bottlenose dolphin is Tursiops truncatus. (Sea World,2002) Modern forms of both odontocetes and mysticetes appear in the fossil record five to seven million years ago. The genus Tursiops first appears in the fossil record about five million years ago (Sea World,2002) The bottlenose dolphins are intriguing creatures that are very valuable in the research and knowledge of waters of the earth.
Dolphins inhabit the temperate and tropical waters throughout the world. (Sea World,2002) The Pacific Ocean inhabits many dolphins that range from California and Northern Japan to Australia and Chile. Some are found even as far as the Hawaiian Islands. The Atlantic Ocean houses bottlenose dolphins from Nova Scotia and Norway to the tip of South Africa. The Indian Ocean and the Mediterranean Sea also house bottlenose dolphins. Bottlenose dolphins found in the United States are abundantly located from Cape Cod to the Gulf of Mexico.
(Sea World, 2002) The pelagic zone as well as harbors, bays, lagoons and gulfs are the habitats for dolphins. Two ecotypes are found in the oceans. The coastal ecotype is adapted for warm, shallower waters. Because of the depth, the size is usually smaller, yet the flipper size larger to allow for increased maneuverability and heat dissipation. These dolphins are found in harbors, bay, gulfs, and estuaries. The offshore ecotype is adapted for cooler, deeper waters. The larger body helps to conserve heat and defend itself against predators. (Sea World, 2002)
Seasonal movements of dolphins to and from certain areas is called migration. Migration is usually caused by change in temperature, migration of food, and feeding habitats. Dolphins found in higher lattudes migrate south to warmer waters. This migration is a much longer distance than dolphins found in southern, warmer areas.(Sea World, 2002) When dolphins migrate they move in packs called pods. A pod is a group of dolphins that include the males, females, and the young called calves. The pod usually consists of twelve dolphins, but some may grow to be as large as one hundred or up to one thousand. (Encyclopedia,1994) In the wild, pod composition and structure are based largely on age, sex, and reproductive condition (Wells, 1991).These pods of dolphins make up a large population. Because bottlenose dolphins are not endangered, they have a large population which is unable to be determined. But some locations have estimations. The Gulf of Mexico is estimated at least 67,000. The populations found in the western North Pacific and along Japanese coasts are estimated at about 35,000. (Sea World, 2002) The large population of dolphins has allowed significant leaps in research of these mammals.
Dolphins have streamlined and elongated bodies. They are torpedo shaped which allow for faster and easier movement. They have paddle shaped forelimbs located laterally on each side of their bodies. The forelimbs called flippers are for balance as well as making sharp turns and sudden stops. Dolphins can reach speeds up to twenty to twenty-five miles an hour, although for only a short amount of time. (Encyclopedia,1994) Pectoral flippers have all the skeletal elements of the forelimbs of terrestrial mammals, but they're foreshortened and modified.(Sea World,2002) The skeletal elements are supported by connective tissue and cartilage pads.The dorsal fin located on top of the back behind the blow hole is also used for balance. Flukes are flattened pads of tough, dense, fibrous connective tissue, completely without bone or muscle. Each lobe of the tail is called a fluke. The spread of the fluke is twenty percent of the body length which creates propulsion. To propel the dolphin the fluke is moved up and down instead of the common movement of fish which is side to side. Longitudinal muscles of the back and caudal peduncle move the flukes. (Sea World,2002) The dorsal fin is located on the back of the dolphin behind the blow hole. Although it is not a necessary fin, it is used for balance. The dorsal fin is constructed the same as the pectoral fins, dense fibrous connective tissue, with no bones.
Dolphins have skin that is very smooth and rubbery. (Encyclopedia,1994) Although most mammals are characteristic for hair, only some species of dolphins have sparse sensory bristles(verbrissae) on their head surface. ( Reeves, 2002) The coloration of the skin is a gray to gray-green or gray-brown on the top that fades to a white on the underneath, under the nose, and anal region. This coloration is used as camouflage from their predators, sharks. From above the water the dolphin is camouflaged by the dark color blending in with the dark depth. When looking underneath the dolphin, it’s light belly region blends with the bright color from the surface of the water.(Sea World,2002) Underneath the skin is a layer of blubber. This is a fatty content that is used to warm the body and storage of food and energy. Blubber is lighter that water, which probably helps in the flotation of dolphins. The entire body of a dolphin is very keen to touch. (Encyclopedia,1994)
The teeth of dolphins are one of the most important features for its survival. The teeth are conical and interlocking. The number of teeth range from twenty to twenty-five on each side of the upper jaw and eighteen to twenty-four teethe on each side of the lower jaw. This amounts to a total number of seventy-six to ninety-eight teeth. Dolphins use their teeth for grasping food, not chewing. Food is swallowed whole and usually head first so the spines of the fish do not catch on their throat. Dolphins eat a variety of fish, crustaceans such as shrimp, and squid. Dolphins consume about four to five percent of their body weight per day. Dolphins feed on schools of fish and individuals. Pods heard schools of fish by encircling them then use their flukes to stun fish. Once encircled the dolphins each take turns charging through the school. Bottlenose dolphins may also stun larger fish by throwing them out of the water with their flukes. Because the sense of smell and sense of taste work together, both are limited in the dolphin.The sense of smell is present because olfactory lobes of the brain and olfactory nerves are absent in all toothed whales, indicating that they have have a limited sense of smell.(Sea World,2002) There is a presence of taste buds on the dolphins tongue but there is little studied if they are used. Dolphins do show strong preferences for certain species of food fishes (Barros and Odell, 1990).
Bottlenose dolphins have senses similar to humans. Hearing is very important to the mammal. Dolphins have very well-developed hearing because the auditory cortex of the brain is highly developed. The auditory nerve in dolphins which may have 67,900 or more cochlear fibers, this is approximately twice the amount in humans.(Sea World,2002) Bottlenose dolphins respond to tones within the frequency range of 1 to 150 kHz. The average hearing range for humans is about .02 to 17 kHz.(Sea World,2002) Dolphins have a much higher hearing ability than humans. Dolphins have small ear openings approximately one inch behind the eye. There are no external ear flaps. (Reeves,2002) The small ear leads to a reduced ear canal and ear drum. The most receptive part of the dolphin to sounds is the lower jaw. The lower jaw receives frequencies above twenty kHz. A fat-filled cavity in the lower jaw conducts sound waves through the jaw and sent to the middle ear.(Sea World,2002) The eyesight of a dolphin is very acute. They are able to see both in and out of water, but their eye sight is mainly adapted for water. certain features of the lens and cornea correct for the refraction of light caused by the transition from aquatic to aerial vision. Without this adaptation, a dolphin would be nearsighted in air.(van der Pol, Worst, and van Andel, 1995) Bottlenose dolphins have a retina that contains both cone cells and rod cells. This allows them to see both in bright and dim light. The presence of cone cells suggests that dolphins can see in color, but no studies have proved this idea. (Ridgway, 1990)
The behavior of dolphins has been a topic researched for years. Dolphins exhibit similar behavior to humans. Both humans and dolphins show bonds with significant others. A mother and calf bond are long lasting. A calf stays with its mother for three to six years or more.(Wells, 1991). Adult male bonds are also long lasting. Behavioral studies suggest that certain animals prefer association with each other and recognize each other after periods of separation.(Sea World,2002) To establish a hierarchy order, bottlenose dolphins bite, chase, jaw- clap, and smack their tails on the water (Shane, et al., 1986; Herman, 1980). Dolphins show their aggression by scratching with their teeth which leaves marks on the skin. Courtship is shown by head-butting, nuzzling, twisting and tooth-scratching.(Shane, et al., 1986). Individuals have been seen riding the bow waves of boats. They also breach which is when the jump or leap in the air and land on their backs. Dolphins can get as high as sixteen feet. Fluking is when they lift their flukes above the surface was they begin to dive. Lob tailing is when they slap the water with their flukes. (Reeves,2002) Dolphins also play together by tossing objects such as seaweed to one another. This is also a method to practice catching food. (Sea World,2002)
Sexual maturity is when the dolphin becomes old enough to reproduce. Females usually reach this point between five and twelve years old. Males reach sexual maturity when they are ten to twelve years old.(Mead and Potter, 1990; Odell, 1975). Females usually initiate the courtship and breeding behavior. This breeding behavior occurs throughout the year. Once courtship is initiated the gestation period begins which last for ten to twelve months.(Encyclopedia,1994) Only on calf is born at a time but a female bears a calf about every three years. A calf is born either head-first or tail-first. Right after delivery a calf swims to the surface for its first breath of air.(Encyclopedia,1994) The calf is approximately forty-two to fifty-two inches long and weighs about forty-four pounds.(Sea World,2002) Mothers nurse the young from their nipples for the first four to eight days. As the calf develops it becomes more independent from its mother.
Echolocation is the method used by dolphins to locate objects under water. Dolphins use series of clicks to locate the object. The melon which is located in the front of the head is where the sounds leave from. A special fatty tissue directs the sounds forward. Echoes produced by the sounds bouncing off of objects directs the dolphin in the direction needed. (Encyclopedia,1994) By this complex system of echolocation, odontocetes can determine size, shape, speed, distance, direction, and even some of the internal structure of objects in the water.(Sea World,2002)
Dolphins usually live for a life span of twenty years or less. Some dolphins have been recorded to live as long as forty-eight years.(Duffield and Wells, 1990).To estimate this life span scientist look at a spliced tooth. Each year another layer is added on to the teeth. Scientists look and count the amount of layers for each year. This is similar to telling the age of a tree. Dolphins may suffer from viral, bacterial, and fungal infections. In addition, they may develop stomach ulcers, skin diseases, tumors, heart disease, urogenital disorders, and respiratory disorders.(Sea World,2002) Beaching is also another cause of death because a dolphin when stranded on the beach becomes over heated which kills the dolphin.(Encyclopedia,1994) Certain large shark species are predators of bottlenose dolphins. Dolphin remains are often found in the stomachs of tiger sharks, dusky sharks, and bull sharks .(Shane, et al., 1986)
Humans have a large impact on the longevity of dolphins. Dolphins that are coastal live with in the polluted bays and gulfs. Heavy boat traffic, habitat destruction and competition with fisheries affects dolphins. (Sea World,2002) dolphins are also caught in fishing net that were intended to catch tuna fish, cod, salmon, mackerel. In 1972, a law was passed to limit the number of dolphins that could be killed by fishing crews. Also in 1990, tuna companies refused tuna fish nets that had killed dolphins in the process of collecting and catching fish.(Encyclopedia,1994) Many organizations have been started to help prevent the killing of dolphins. As humans it is our job to protects the animals that we have on earth today because they may not be there tomorrow.
“Bottlenose Dolphins.” 2002: pps. 1-10. June 9, 2003. .
Duffield, Deborah A. and Randall S. Wells. Bottlenose Dolphins: Comparison of Census Data From Dolphins in Captivity With a Wild Population." IMATA Proceedings, 1990.
Mead, James G. and Charles W. Potter. "Natural History of Bottlenose Dolphins Along the Central Atlantic Coast of the United States." In The Bottlenose Dolphin, edited by Stephen Leatherwood and Randall R. Reeves, pp. 165-195. San Diego-. Academic Press, Inc., 1990.
Odell, Daniel K. “Dolphins.” World Book Encyclopedia. 1994 ed.
Reeves,Randall R., Stewart, Brent S., Clapham, Phillip J., and Powell, James A. “Guide to Marine Mammals.” Chanticleer Press Inc. New York, 2002.
Ridgway, Sam H. "The Central Nervous System of the Bottlenose Dolphin." In The Bottlenose Dolphin, edited by Stephen Leatherwood and Randall R. Reeves, pp. 69-97. San Diego: Academic Press, Inc., 1990.
Shane, Susan H. "Behavior and Ecology of the Bottlenose Dolphin at Sanibel Island, Florida." In The Bottlenose Dolphin, edited by Stephen Leatherwood and Randall R. Reeves, pp. 245- 266. San Diego: Academic Press, Inc., 1990.
Shane, Susan H., Randall S. Wells, and Bernd WOrsig. "Ecology, Behavior and Social Organization of the Bottlenose Dolphin: A Review," Marine Mammal Science 2(l), 1986, pp. 34-63.
van der Pol, Bert A.E., Jan G.F. Worst, and Pek van Andel. "Macro-anatomical Aspects of the Cetacean Eye and Its Imaging System." In Sensory Systems of Aquatic Mammals, edited by R.A. Kastelein, J.A. Thomas, and P.E. Nachtigall, pp. 409-414. Woerden, The Netherlands-. De Spil Publishers, 1995.
Wells, Randall S. "The Role of Long-Term Study in Understanding the Social Structure of a Bottlenose Dolphin Community." In Dolphin Societies: Discoveries and Puzzles, edited by K. Pryor and K.S. Norris, pp. 199-225. Berkeley: University of California Press, 1991.
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