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Bottlenose Dolphin: Natural History and Ecology

The Bottlenose dolphin is one of the most closely studied cetaceans in the world. At the Kewalo Basin Marine Mammal Laboratory and The Dolphin Institute, we have made many valuable discoveries about the sensory systems and cognitive capacities of these animals. Other marine mammal researchers from all over the world have also made major contributions to what we know about the bottlenose dolphin. In this section, you'll find the most up-to-date information about the bottlenose dolphin's natural history and ecology, including:

  • Distribution and Systematics
  • Life History and Reproduction
  • Feeding
  • Predators
  • Social Relationships

Distribution and Systematics

The bottlenose dolphin is a cosmopolitan species, in temperate to tropical zones. In the Atlantic they range from Norway and Nova Scotia to Patagonia and South Africa, including the Mediterranean Sea; in the Pacific from Northern Japan and Southern California to Australia and Chile; and in the Indian Ocean from Australia to South Africa. A coastal and an offshore form of the species are generally recognized, with differences found in gross morphology, hematology, cranial morphology, and parasite faunas. Nuclear and mitochondrial genetic distinctions between offshore and inshore bottlenose dolphins have also been described.

The bottlenose dolphin (Tursiops truncatus) is a member of the order Cetacea, which includes all whales and dolphins. Cetacea is further divided into to the suborders odontoceti and mysticeti. Dolphins are odontocetes, or toothed whales; mysticetes, or baleen whales, utilize baleen (thick keratinized plates) to feed. Bottlenose dolphins further belong to the family Delphinidae, the oceanic dolphins; they are the only species in their genus. Several potentially separate species of bottlenose dolphins have been described, though a general consensus has yet to be reached. Tursiops aduncus is found in the Indian Ocean and the tropical Western Pacific ocean; some data from genetic studies indicate that T. aduncus may actually be more closely related to the genus Stenella (which includes the striped, spotted and spinner dolphins). Some researchers refer to the Pacific bottlenose dolphin as Tursiops gilli, though again it is unclear whether T. gilli actually represents a separate species.

Life History and Reproduction

Bottlenose dolphins are estimated to live into their forties and fifties; researchers in Sarasota Bay, Florida, found that females can live for over fifty years and males for over forty years. Sexual maturity in females occurs between five and thirteen years of age, and between eight to thirteen years for males. Mating and calving times can vary throughout the year but births are predominately recorded in the spring and fall. Females are seasonally polyestrous and spontaneous ovulators, generally ovulating between two and seven times per year with an average cycle length of thirty days. Males display seasonal changes in their testosterone levels as well.

Bottlenose dolphins have a twelve month long gestation period, and calves remain with their mothers for several years. Young nurse, or attempt to nurse, for three to five years, and usually begin playing with and eating small fish around six months of age.

Feeding

Bottlenose dolphins feed on a wide variety of fish and cephalopods (such as squid), and occasionally shrimp and small rays and sharks. They employ a diverse repertoire of feeding behaviors, including both solitary and social feeding strategies. Some of these strategies include:

  • strand feeding in the tidal creeks of South Carolina and Georgia, where dolphins pursue schools of mullet onto mud banks and beach themselves to catch the fish
  • crater feeding, where dolphins use echolocation to detect prey in underneath the sand and dig the prey out with their rostrums
  • "whacking" fish with their flukes to stun them
  • circling entire schools of fish while one dolphin at a time darts in to feed
  • cooperative feeding with humans; in a town called Laguna, Brazil, dolphins and human fishermen have evolved a feeding strategy where dolphins herd schools of fish into the waiting nets of fishermen. The fishermen wait for a signal from the dolphins to throw their nets at the appropriate time; the fishermen take home a sizeable catch, while the dolphins feed on the disoriented fish that escape the nets. This relationship has been ongoing since 1847, with humans and dolphins passing the knowledge down through generations.
    Finally, some individuals in Shark Bay, Australia, have been observed carrying sponges on their rostrums; it is hypothesized that they may use the sponge to protect their rostrum while foraging on the bottom. If so, this represents the first observed case of tool use by wild dolphins.

Predators

Sharks are the primary natural predator of bottlenose dolphins. Bull sharks, tiger sharks, dusky sharks and great white sharks most commonly prey on the bottlenose dolphin. Some evidence exists that killer whales and false or pygmy killer whales may also be natural predators of bottlenose dolphins; scarring consistent with killer whale and false or pygmy killer whale teeth have been observed on dolphins, though no attacks have been documented. However, humans most likely pose the greatest threat to bottlenose dolphin in the wild; see our conservation section for more information.

Social Relationships

The social relationships of bottlenose dolphins in the wild have been intensely studied in two locations: Sarasota Bay, Florida, and Shark Bay, Australia. Researchers in these two locations have discovered much of what we know about the social lives of bottlenose dolphins through long-term field studies. These studies rely on photo-identification of the dorsal fins of individual bottlenose dolphins. Through documenting every sighting of each catalogued dolphin over many years, researchers are able to put together life histories of individual dolphins and identify which dolphins are maternally related. Further, through these field observations, information on the social, reproductive, foraging and predator avoidance behaviors of these dolphins has been acquired. In Sarasota Bay, Florida, researchers led by Dr. Randy Wells of the Mote Marine Lab have studied the resident community of 100 bottlenose dolphins since 1970. Here, researchers have found that females have a large network of associates, but associate most strongly with a group of females called a "band." These bands form the core of the Sarasota Bay community. Males, on the other hand, often form very strong associations with another adult male; these male pairs can endure for many years. In Shark Bay, Australia, a research team including Dr. Rachel Smolker, Dr. Richard Connor, Dr. Janet Mann, and Dr. Vincent Janik have studied the resident population of over four hundred individually identified bottlenose dolphins since 1984. They have found similar associations between females in Shark Bay as those found in Sarasota Bay. Shark Bay males also form strong associations with one or two other males, and these males engage in herding behaviors towards female dolphins. Interestingly, these male coalitions can also band together to form larger coalitions, called alliances, to capture females from other coalitions or to defend their females from competitors. These alliances are temporary and allegiances can switch in a matter of hours.

The bottlenose dolphin is likely to continue to be one of the most frequently studied cetaceans in the wild; its distribution in warm, coastal waters makes it a popular candidate. Even more, KBMML and TDI's ongoing research on the cognitive capabilities of the bottlenose dolphin helps to illuminate field observations and inspire new research in the field. For further information on the natural history and ecology of bottlenose dolphins, the following texts may be very useful:

Reynolds, John E., Wells, Randall S., and Eide, Samantha D. 2000. The Bottlenose Dolphin: Biology and Conservation. The University Press of Florida, Miami, Florida.

Mann, Janet, Connor, Richard C., Tyack, Peter L., and Whitehead, Hal, editors. 2000. Cetacean Societies: Field Studies of Dolphins and Whales. University of Chicago Press, Chicago, Illinois.

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