Individual dolphins along the British, Irish, American and Australian coasts regularly allow people to approach, taking them for rides through the water and sometimes presenting them with gifts of live fish.
Off Hawaii and the US east coast, trained dolphins perform military test manoeuvres in the open sea, while in the Persian Gulf, they are reported to have searched for mines.
In the Caribbean, off Hawaii and wherever large whales such as humpbacks gather, dolphins can be found, swimming circles around the whales and stealing rides by coasting beside them and bow- riding in the pressure waves they create. On the tropical mating grounds, they linger near the humpback singers, perhaps enjoying the concert.
This astonishing variety of behavior provides but a brief glimpse of the versatile, infinitely adaptable bottlenose dolphin. More than any other dolphin, the bottlenose forms long-term associations with such widely different species as sea turtles, humpback whales and humans. But the intimate patterns of daily dolphin life change from place to place, from day to day and from individual to individual. So varied is this dolphin's behavior that it is sometimes difficult to determine patterns at all.
The bottlenose dolphin is the species most familiar to humans, because it has been shown in aquariums since the 1860s. Its apparent adaptability to captive life has proved valuable for researchers. More than 100 bottlenose dolphins have been born in aquariums, and some of those calves have matured, mated and themselves given birth in captivity.
Much of what we know about the social life of all dolphins is the result of studies of wild bottlenose dolphin societies. In the early 1970s, researchers Randall Wells, Michael Scott and Blair Irvine began to visit the bottlenose dolphin population living in the shallow bays off the west coast of Florida, near Sarasota. Using photographs, they identified each animal and, at times, tagged and radio-tracked them. When the scientists could recognize individual dolphins, they were able to define the population and the social groupings and to monitor the comings and goings of the members. The researchers also captured known individuals, took blood samples for genetic analysis, then released the dolphins. From such studies, we have learned:
the bottlenose dolphins that live around sarasota form a relatively stable unit of about 100 individuals. This population has its own home range but shares its borders with other bottlenose dolphin communities. The older males, in particular, live along the borders and visit back and forth. In this way, there is some genetic mixing between adjacent groups, which is healthy for the population. Still, most social interactions occur within each community.
Mothers and their calves develop strong bonds that last three to six years, long past the estimated weaning age of 18 to 20 months. Young male and female adults swim in mixed subgroups. Males, however, gradually form their own buddy groups. Two or three males of the same age may stay together into adulthood - sometimes for life. Young females, meanwhile, travel with other sub-adults until they calve at 8 to 12 years of age. Then they join bands of adult females and their young.
In the Sarasota community, there are three of these bands, each composed mainly of related females that remain in the same core area. The adult males - either alone or in buddy pairs or trios - move from one band to another and occasionally visit bands in other communities.
A rich overall picture of a bottlenose dolphin community is emerging from the life histories of so many individuals. Some animals, whose teeth have been examined for growth layers, are known to be in their late forties. To learn more about these and other bottlenose dolphin communities simply requires time and clever strategies that will allow us to study the dolphins with minimal disturbance to their lives.
Research on the social behavior of dolphins is also being conducted off the coasts of Texas, California, Portugal, Great Britain, Western Australia, Chile, South Africa and Argentina, among other areas. While these studies confirm many of the Florida findings, each has revealed some tantalizing new information. Off Western Australia, for example, the bottlenose dolphins have become so tame that it is possible to approach them in small boats and even to wade among them in shallow water. Such observations have begun to unlock the mysteries of how dolphins form friendships with each other and compete for mates.
What we know about the "mind" of the dolphin comes from these studies - particularly those concerning bottlenose dolphin individuals kept captive as part of scientific programmes, for military research and as aquarium performers. Our research findings on dolphin communication, courtship, mating and motherhood are, for the most part, courtesy of the cooperative nature of bottlenose dolphins.
Yet the benefits of a close association between humans and bottlenose dolphins may prove to be tragically one-sided. Along the east coast of the United States, from New Jersey to Florida, roughly 750 bottlenose dolphins washed up dead in late 1987 and early 1988. Researchers determined that a number of factors had led to a weakening of the dolphins' immune systems and their eventual deaths, including red-tide toxins and possibly contaminants such as PCBs picked up in fish they had eaten. Meanwhile, the offshore bottlenose dolphins, a separate population, were apparently unaffected.
Aquarium performer, occasional wild companion to humans, source of inspiration - the bottlenose is a high-profile, cosmopolitan dolphin. Its adaptiveness as a species has made it successful around the world. While the bottlenose dolphin may be unable to articulate the threat to its habitat, its presence remains one of the best monitors of the health of our shores.
Size: 2.3 to 3.1 m, 150 to 275 kg. Males larger than females
Calves at birth: 98 to 130 cm
Teeth: 18 to 26 teeth on each side of upper and lower jaws
Food: Fish (mullet, anchovies, herring, cod, menhaden and a wide variety of other species) and squid
Habitat: Mainly coastal but also offshore waters
Range: World ocean except polar seas
Status: Population unknown. Declines noted in some areas, but common in most parts of its range
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