Bottlenose Dolphin
Tursiops trunsatus
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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.
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 coast line. 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.
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 and cod fish, and squid. Those found in coastal Atlantic waters feed on mullet, herring, smelt, capelin, catfish, eels, shrimp, and other crustaceans.
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.
Also known as the Bottlenosed Porpoise, Gray Porpoise, Common Porpoise, and Black Porpoise. The name may be prefixed by "Atlantic" or "Pacific".
There are many records of wild individuals voluntarily approaching humans closely enough to be touched. While these dolphins do communicate among themselves (as probably all cetaceans do), there is no good evidence that they talk to people.
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.
It is possible for bottlenose dolphins to live into their 40's, much the same as humans may live into their 90's. The oldest bottlenose dolphin to be scientifically aged was 48 years old at the time of death.
"The Audubon Society Field Guide to North American Fishes, Whales & Dolphins", Copyright Chanticleer Press, Inc. 1983. All rights reserved.
"The Whale-Watchers Handbook: A Field Guide to the Whales, Dolphins, and Porpoises of North America", by David K. Bulloch, Copyright 1993, All rights reserved.
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