Dolphins
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in seventeen genera. They vary in size from 1.2 metres (4 ft) and 40 kilograms (88 lb) (Maui's Dolphin), up to 9.5 m (30 ft) and ten tonnes (the Orca or Killer Whale). They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating fish and squid. The family Delphinidae is the largest in the Cetacea, and relatively recent: dolphins evolved about ten million years ago, during the Miocene. Dolphins are considered to be amongst the most intelligent of animals and their often friendly appearance and seemingly playful attitude have made them popular in human culture.
The scientific order 'Cetacea' is comprised of whales, dolphins, and porpoises. These aquatic creatures are the most specialized of all mammals, with adaptations that allow them to spend their entire lives in water. Living cetaceans are divided into two distinct suborders, Mysticeti and Odontoceti, which are divided further into a total of thirteen families. The Mysticeti suborder contains those whales, which have baleen plates instead of teeth. A baleen whale feeds by straining water through the baleen, trapping the fish, shrimp, crustaceans, or krill inside its mouth. This suborder is comprised of the largest whale species, including the blue whale, the humpback whale, and the grey whale.
Those cetaceans classified in the suborder Odontoceti are toothed whales, dolphins, and porpoises. They are generally smaller, faster, and more agile than their baleen counterparts. Scientists have identified approximately 80 species of toothed whales, ranging in size from the 60-foot sperm whale to the five-foot harbor porpoise. The various species are incredibly diverse and display a multitude of body shapes, behavior patterns, and lifestyles. Some spend barely any time on the surface, rising occasionally to take a breath; others can leap 20 feet out of the water almost effortlessly. Some species live in the shallows close to shore, some reside in deep oceans, and still others are found only in fresh water rivers. Odontoceti may have anywhere from eight to 250 teeth, and their eyesight ranges from poor to excellent.
Dolphins emit pulses of sound from the melon, a fatty area just below the blowhole. Much like the orientation vocalizations of a bat, these pulses, or clicks, return as echoes when the sound bounces off objects in the dolphin's path. The animal uses the echoes to navigate and to judge the distance to, and location of, prey as small as shrimp. Dolphins also produce whistling sounds when excited or communicating with other dolphins. These sounds arise from the larynx.
Dolphin (aquatic mammal), fast-swimming animal related to whales and porpoises. Sleek and powerful swimmers found in all seas, dolphins are distinguished from porpoises by well-defined, beaklike snouts and conical teeth. The porpoise has a blunt snout, chisel-shaped teeth, and a stouter body.
There are approximately 57 species of dolphins. Most have an elongated beak called a rostrum. The difference between porpoise and dolphin is in the shape of the teeth. Dolphins have cone shaped teeth whereas porpoise have spade shaped teeth. Most porpoise live in colder waters and are smaller than most dolphins, and they have no elongated beak.
The largest of all Dolphins is the Orca, or Killer Whale. It is the most powerful creature that lives in the oceans. It is the fiercest of sea predators and fears no other creature whatsoever.
Typical examples are the bottle-nosed dolphin, a popular performer in seaquariums, and the common dolphin, which inspired many Mediterranean folk legends. Both often appear in open waters, making their characteristic arched bounds, frequently before the bow waves of ships. Several freshwater species inhabit river estuaries in Asia and South America.
The small, graceful tucuxi dolphin has been sighted more than 2000 km (more than 1250 mi) up the Amazon River. The tucuxi, the smallest dolphin, is less than 1.2 m (less than 4 ft) long; the largest, the bottle-nosed dolphin, reaches a length of 3 m (10 ft). The killer whale is considered a dolphin despite its much greater length of 9 m (30 ft). The pilot whale is also considered a type of dolphin.
Dolphins once were hunted commercially, especially for the small quantity of valuable oil extracted from parts of the head and used to lubricate delicate watch mechanisms. Cheaper oils have now been found from other sources, and dolphins are no longer hunted for this reason. Many dolphins, however, become accidentally trapped and drowned in tuna nets; between 1959 and 1972 an estimated 4.8 million dolphins died in this way.
Under pressure from animal rights activists and United States consumers, both domestic and international tuna canners have refused to accept shipments from fishing fleets that do not protect dolphins. Concern has also been expressed about the treatment of dolphins on display in public aquariums and in ³swim with the dolphins² programs. The Marine Mammal Protection Act of 1972, amended in 1988 and 1992, was passed to prevent exploitation of dolphins and related aquatic animals. The National Marine Fisheries Service is the principal regulatory agency.
Behavior
In one day dolphins eat an amount of food, mostly fish and squid, equal to nearly one-third of their weight. Dolphins are swift enough to easily outdistance their prey. They seize their catches with jaws that have from 200 to 250 sharp teeth. Dolphins follow schools of fish in groups of varying size. Some species, such as the Pacific white-sided dolphin, make up aggregations estimated at tens of thousands of members. Less gregarious species, such as the bottle-nosed dolphin, join in groups that often contain only a few members.
Dolphins, like whales, breathe through a blowhole at the top of the head. As they travel they break surface about every two minutes to make a short, explosive exhalation, followed by a longer inhalation before submerging again. The tail, like that of other aquatic mammals, strokes in an up-and-down motion, with the double flukes driving the animal forward; the flippers are used for stabilization. Dolphins are superbly streamlined and can sustain speeds of up to 30 km/h (up to 19 mph), with bursts of more than 40 km/h (more than 25 mph). Their lungs, which are adapted to resist the physical problems created for many animals by rapid changes in pressure, enable them to dive to depths of more than 300 m (more than 1000 ft).
Adults of the bottle-nosed dolphin‹the best-studied species‹come to sexual maturity after 5 to 12 years in females and 9 to 13 years in males. They mate in the spring; after a gestation period of 11 or 12 months, a single calf is born, tail first. Calves swim and breathe minutes after birth; they nurse for up to 18 months. They are able to keep up with the mother by remaining close and taking advantage of the aerodynamic effects of the mother's swimming.
Vocalizations and IntelligencePrint section
Dolphins almost constantly emit either clicking sounds or whistles. The clicks are short pulses of about 300 sounds per second, emitted from a mechanism located just below the blowhole. These clicks are used for the echolocation of objects and are resonated forward by the so-called oily melon, which is located above the forehead and acts as an acoustic lens. Echoes received at the area of the rear of the lower jaw are transmitted by a fat organ in the lower jaw to the middle ear. This echolocation system, similar to that of a bat, enables the dolphin to navigate among its companions and larger objects and to detect fish, squid, and even small shrimp. The whistles are single-toned squeals that come from deeper in the larynx. They are used to communicate alarm, sexual excitement, and perhaps other emotional states.
Because of the ability of dolphins to learn and perform complex tasks in captivity, their continuous communications with one another, and their ability, through training, to approximate the sounds of a few human words, some investigators have suggested that the animals might be capable of learning a true language and communicating with humans. Most authorities, however, agree that although the dolphin's problem-solving abilities put the animal on an intelligence level close to that of primates, no evidence exists that dolphin communications approach the complexity of a true language.
The name dolphin is also applied to food fish of a different genus that have long, continuous dorsal fins. The fish, found worldwide in tropical marine waters, can reach a length of 1.5 m (5 ft).
Scientific classification: Dolphins belong to the suborder Odontoceti of the order Cetacea. The bottle-nosed dolphin is classified as Tursiops truncatus, the common dolphin as Delphinus delphis, and the tucuxi dolphin as Sotalia fluviatilis. The killer whale is classified as Orcinus orca. Pilot whales make up the genus Globicephala. The white-sided dolphin is classified as Lagenorhynchus obliquidens.
~ Encyclopedia Encarta
Body roughly cone-shaped in front of the flipper;beak long and slender, withno crease separating it from the forehead, as there is in most dolphins;body often covered with yellowish white blotches;lips and tip of snout white;eyes dark;distribution primarily pelagic, in tropical to warm temperate regions.
Similar to Tursiops truncatus, except for smaller, nearly triangular dorsal fin, and tooth count, having 26-35 pairs in each jaw;limited to rivers and floooded jungles, as well as nearshore marine waters of northeastern South America and eastern Central America.
Dorsal fin at midback consists of a long,ridged base surmounted by a small triangular of falcate fin-tip in adults,west of Indonesia;east of Indonesia the hump is lacking, but the fin is more pronounced;many animals have a speckled appearance;found in coastal waters of of West Africa and in Indo-Pacific;there appear to be two groups of undescribed relationshop in the Indo-Pacific,one west of Indonesia,one east and south of Indonesia.
Short,thick beak,white or light gray on European side of range, sometimes dark off North America;two white or gray areas on each side of body,one in front of,and the other behind and below,the dorsal fin;posterior light area continues onto dorsal aspect of caudal peduncle;limited to northern North Atlantic.
Narrow white patch on flanks;yellow or tan streak above white patch extending up toward ridge of tail;short,bicolored beak;limited to northern North Atlantic.
Lack of a prominent beak;erect,slightly hooked,two-tone dorsal fin; a pair of gray"suspenders"along the back;two dark,shadowlike blazes at midflank pointing tailward;found in temperate southern hemishere.
Short,thick beak,clearly demarcated from forehead;dorsal fin sharply hooked,usually dark on leading edge,lighter posteriorly;back dark,but with two stripes or"suspenders"from head to near tail;distribution limited to North Pacific.
Sharply demarcated black-and-white coloration,with dorsal and ventrolateral dark zones meeting at midflank,separating white sides into anterior and posterior zones;found only in high latitudes of southern hemisphere.
Similar to L.obscurus,but coloration muted;black face and throat; conspicuous dark,diagonal flank patch,above which is a white patch narrowing anteriorly;small white patch above and behind flipper;found only in coastal waters of southern South America and in the vicinity of the Falkland Islands.
Short beak;relatively small flippers,flukes,and dorsal fin(subtriangular); wide,prominent eye-to-anus black band;stocky build;tropical distribution.
Conspicuous white thoracic patch;V-shaped black or dark-gray saddle with downward-oriented apex on sides directly below dorsal fin;light gray of flank sweeping over dorsal aspect of tail stock;hourglass effect on side, with tan or yellowish tan region making up posterior half of hourglass; absent from high latitudes,but otherwise cosmopolitan.
White or light-gray coloration of adults,usually interrupted only by dark dorsal fin,flippers,and flukes;tall,falcate dorsal fin;extensive scarring on adults;lack of beak;squaris melon bisected by deep crease;primarily found in deep tropiccal and warm temperate waters worldwide.
Body usually spotted,differing by region and age;spotting generally decreases with distance from continental shores of Notth America,but within populations increases with age;beak long and slim;distribution primarily tropical but includes some warm temperate waters in Atlantic; distribution primarily oceanic.
Black lateral stripes from eye to flipper and eye to anus;white v-shaped "shoulder blaze,"originating above and behind the eye,and narrowing to a point below and behind the dorsal fin. Primarily tropical to warm temperate distribution.
SHORT-SNOUTED SPINNER (or Clymene)DOLPHIN
Long,slim snout(longirostris only);lips and tio of snout dark;habitually jumping and spinning on longitudinal axis;dorsal fin usually tiangular or canted slightly forward,often with a light spot in center of dark area; tail stock of adult males usually strongly keeled;distribution tropical to warm temperate,primarily in deep water.
No dorsal fin;body slim and graceful;striking black and white coloration; white zones covering head and extending onto sides,including flippers,and onto tail stock;small but distinct beak;limited to temperate portions of the southern hemisphere.
No dorsal fin;body slim and graceful;coloration visible in water primarily blck;small amounts of white ventral hourglass pattern visible around flippers;small but distinct beak;limited to temperate North Pacific.
Low, rounded dorsal fin;no beak;dark pigmentation;limited to the coastal waters of Chile.
Pink Dolphins have the highest spiritual frequency.
Pink Dolphins can be found in the waters off Argentina.
This unique dolphin picture was taken in Hong Kong.
The most common species of coastal dolphins in the Atlantic Ocean and Gulf of Mexico.
The elongated beak gives this name to the bottle-nosed dolphin They are solid gray above, and pale gray to white and pink below.
The bottlenose dolphin, whose scientific name is Tursiops truncatus, is probably the dolphin most familiar to the general population because of its adaptability of living in human care. Bottlenose dolphins can be seen in various show and research facilities and have been the "stars" of many movies and television shows. Because of their seeming curiosity about people and their close proximity to various shores and ocean bays, this species is the most studied of all delphinids. The bottlenose is the dolphin most often sighted off the coast and from small boats. In some places in the world, such as Monkey Mia in Australia, wild bottlenose dolphins choose to come into bays and interact with human beings.
Bottlenose dolphins are the largest of the beaked dolphins. There is a definite crease where the rostrum (snout or beak) joins the melon, and the shape of the mouth seems to form a permanent smile. Their bodies are dark gray on the back and sides, fading to a pinkish white belly underneath. Their dorsal fins are falcate, curving slightly to the back. Pectoral fins and flukes are pointed at the tips. Atlantic bottlenose dolphins are usually 6 to 9 feet long at maturity; the Pacific variety often may be larger.
The exact number of the world population of bottlenose dolphins is unknown. They are found world-wide and in many types of waters from coastal and inshore waters to the pelagic waters of the deep oceans, from warm tropical waters around the equator to the colder temperate regions. In general, bottlenose dolphins can be found in all coastal waters throughout the world, except for the polar seas.
In the Pacific Ocean, bottlenose dolphins range from northern Japan to southern Australia and New Zealand, and from southern California down the coast of Chile. Populations located in the inshore waters of New Guinea and northern Australia often share their range with the Indo-Pacific humpback dolphin, while offshore populations are often seen associating with pilot whales.
In the Atlantic Ocean, bottlenose may be found from Nova Scotia to Norway, extending south to Argentina and the southern tip of South Africa. In the west Atlantic, including both Hudson Bay and the Caribbean Sea, bottlenose dolphins are fairly widespread. Abundant populations are located in Florida's coastal waters and in the Gulf of Mexico. Less commonly, they may be found off the Virginia coast and in Chesapeake Bay. Many offshore populations in the Atlantic coexist with pods of pilot whales or other species. Although bottlenose dolphins were once commonly seen in the coastal waters of the northeast Atlantic, populations along the English Channel coasts seem to have declined. Some offshore groups can still be found, and others exist in bays and estuaries, particularly along the coast of western Ireland.
Bottlenose dolphins are also common throughout the Indian Ocean from the coasts of India and Sri Lanka to the southern tips of South Africa and New Zealand. Both inshore and deep water, pelagic populations are well known throughout this area, including the Mediterranean Sea, the Persian Gulf, and the Red and Black Seas. The bottlenose dolphin seems to be one of the most abundant species found in Israeli waters and along the Egyptian coast.
We are far from knowing the precise ranges of the various populations of bottlenose dolphins around the world, especially those who live far from shore. Most, however, seem to prefer a relatively small area within a protected bay or shallow lagoon. They seem to establish a "home base," but must often move within a larger range to find food, to mate, or to escape predators.
Scientists have found that small pods of bottlenose dolphins near San Diego, California seem to have a range of approximately 20 miles along the coastline. When Randy Wells studied bottlenose off Sarasota, Florida, he found that local populations had a range of about 85 square kilometers, with individuals defining smaller home ranges for themselves. He found that distances traveled varied by sex and age of the dolphins: females with calves seemed to have the largest home range (average 40 square km); juvenile males tended to establish a somewhat smaller one; adult male groups, adult females without calves, and juvenile females had the smallest ranges of approximately 15-20 square km. Each subrange of the larger pods was centered in different areas, possibly due to the fact that dolphin pods tend to be segregated by sex and age. Other studies in Argentina, Texas, and California had similar results and have promoted the theory that social units of like sex and age tend to define the home ranges of various pods.
Feeding Most Odontoceti (toothed whales) feed on various types of fish or squid, although the Orca also will prey upon birds and other marine mammals, often many times larger than itself. The various species of toothed whales have long rows of sharp teeth, suitable for grasping quick-moving prey such as fish and squid. They do not chew their food, but swallow it whole, using muscles at the back of their tongue and throat to squeeze the salt water out and the fish down. The preferred food of a particular species or stock depends on its physiological feeding apparatus, the ecology of the area in which it is located (water temperature, terrain, depth), and the feeding behaviors practiced by that group.
Diet may indirectly determine the size of a pod. For example, the largest toothed whale, the sperm whale, feeds on giant squid of over 12 meters in length which are found at great depths and do not occur in large numbers. Sperm whales may travel individually or with only one or two other whales to facilitate finding enough food. An average pod of pelagic dolphins that eat small squid usually numbers less than 100, depending on the concentration of squid in any particular area. The common, spinner and spotted dolphins feed on shoaling fish and may travel in pods numbering in the thousands.
The natural diet of the bottlenose dolphin seems to vary according to its home region. Open water pods tend to feed mostly on pelagic fish, such as blue whiting, cod fish, and squid. Those found in coastal Atlantic waters feed on mullet, herring, smelt, capelin, catfish, eels, shrimp, and other crustaceans. In the Indian Ocean, dolphins will be more likely to feed on coral reef dwelling fish and mullet. Haddock, anchovies, and mackerel also seem to be favorites of some populations.
Dolphins usually forage for food in groups. Because fish tend to be distributed throughout their range in ever-moving schools, they must search for their prey. If they remained in only one small area constantly, they would soon exhaust the available food supply; therefore, they tend to leave and then revisit various feeding grounds on a periodic basis. By hunting cooperatively in groups, dolphins can cover a wider area and combine their collective experience. Knowledge of topographical features of the area, as well as their ability to scan the area acoustically under water, contribute to their ability to find food. Most dolphins and fish- or squid-eating small whales travel in groups which are broader than they are long, enabling them to scan a wider area with their echolocation.
In the waters of South Africa, researchers have observed a single line of approximately 200 bottlenose dolphins traveling quickly and cooperatively in their search for food. Based on observations of behavior such as synchronous dives and recordings of vocalizations, scientists have theorized that pods of dolphins remain in constant acoustic contact while foraging.
Bottlenose dolphins seem to work together during feeding as well as while searching for fish. Researchers have observed them using a variety of cooperative methods to entrap their prey which reduce the amount of energy expended by any individual. Small groups may converge on a central point by porpoising to that point, and bunching fish up together in the center. Groups have been observed moving synchronously in a U-shaped formation towards other individuals, trapping the fish in between. At times, individuals may dive down and herd a school of fish upwards by swimming around and under them, tightening the circle until the fish are forced to the surface where the rest of the pod is waiting to feed.
Other, more unusual methods also have been noted by researchers. Dolphins have been observed using a sloping, sandy beach as a barrier while herding schools of fish. In some areas, dolphins will chase fish onto mudflats, then actually almost beach themselves by sliding out of the water to seize their prey. Scientists have theorized that some dolphins may use a burst pulse--a stream of very powerful sounds--to stun or confuse their prey.
On the west coast of Africa, bottlenose dolphins even work cooperatively with humans to ensure their food supply. The dolphins herd mullet to the shallows where native fishermen wait with gill nets to trap the fish. The fishermen allow the dolphins to eat their fill, then take the rest. The fishermen apparently can alert the dolphins to feeding time by slapping the water with sticks as a cue for food.
In southern Brazil, bottlenose dolphins have been the initiators of another fishing cooperative. A pod of dolphins alerts the men of Laguna to "feeding time" by stationing themselves offshore in a line. When a dolphin leaves the line, swims seaward, and returns, the men wait close to shore with their nets. When the dolphin reappears, comes to a full stop, and dives just out of net range, the fishermen closest to the dolphin cast their nets, even though the water is murky and they cannot see any fish. The cue given by the dolphins is reliable; few fishermen waste their time casting until instructed to do so by the dolphins' actions. After one or more men fill their nets, others come to take their place. If the dolphins move along the shore, the men will follow. The dolphins seem to take advantage of the confusion which results as the men cast their nets, feeding on their own from the remaining fish. Town records indicate that this partnership has lasted through several generations of both men and dolphins since 1847.
Social Structure and Behaviors
Dolphins tend to be very social animals, swimming in social groupings called pods. These groups, however, are very flexible and fluid, not at all like the social unit we refer to as a family. Dr. Deborah Duffield has determined by observing pods of wild bottlenose dolphins that the majority of pod members are not closely related. They seem to be in a periodic state of flux; an individual dolphin traveling with one group may be swimming miles away with another by the next day. A more stable subgroup of two to six dolphins may remain together over long periods. Mothers and their calves have been observed together for at least three to six years, and unrelated adults often form long-term bonds, usually within the same sex and age group.
Separation by age and sex is common. Breeding groups are usually composed of mothers and their calves. As the youngsters begin to mature, they may branch off into a juvenile pod. Mature males will rarely be seen mixing with a maternity pod or a juvenile pod. The fluidity of the groups, however, allows increased opportunities for mating, enabling males to court a wider variety of females. During feeding, smaller pods may interact and join into larger groups. Bottlenose dolphins also have been observed swimming and feeding with other cetaceans such as sperm whales, gray whales, humpbacked dolphins, and right whales.
Although solitary individuals are sometimes seen in the wild, bottlenose dolphins usually live in pods composed of two to twenty-five dolphins. Inshore groups tend to be smaller, with an average size of ten, but groupings may exist as large as one thousand. The size of the group may depend partially on the need for surveillance against predators, as well as the quantity and distribution of available food.
Dolphins seem to acknowledge a hierarchy within each pod. Status may be expressed by positioning, formation of subgroups within the pod, or by feeding order. Behaviors, such as teeth raking, tail slapping, jaw popping, biting, or ramming may also express dominance.
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