Bottlenose Dolphin (Tursiops truncatus)

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The Bottlenose Dolphin

The Bottlenose Dolphin (Tursiops truncatus) is the most recognizable and well known of all dolphin species since they are most often seen in coastal waters and are the dolphins seen in zoos and other recreational parks. In the Gulf of Mexico and other coastal waters in the Atlantic Ocean, there have been several incidences of large numbers of dolphins dying due to a virus infection. This has been linked to water pollution, and this, along with fishing and human recreation, appears to be one of their greatest threats.

Bottlenose Dolphins are found basically in a band across the middle of the planet in temperate and tropical waters. They are found in almost every ocean and smaller seas, such as the Gulf of Mexico and the Mediterranean Sea. There are estimated to be approximately 67,000 of these dolphins in the Gulf of Mexico alone. They are most often found in small groups of around 20 in shallower coastal waters. There are, however, very large groups of these dolphins, numbering in the hundreds, that live in deeper waters out in the open sea. In some locations, dolphins do migrate, heading to warmer seas in the winter. It seems that those dolphins that live in lower, more tropical waters do not migrate but stay in the same location pretty much all the time.

Bottlenose Dolphins are named for their distinctive faces and the snouts, or beaks, that extend far off of the head, thought to resemble the neck of a bottle. The skin is a gray color, sometimes verging to greenish-gray or brownish-gray, that fades to white on the belly. There is a single, pointed dorsal fin, located in the center of the back, and a blowhole on the top of the head. As dolphins breathe through their blowholes, they are able to close and be completely water-tight when the dolphin is swimming. There are muscles surrounding the blowholes that allow the dolphins to open the holes to take in oxygen. They have relatively small eyes that are located close to their mouths, and their ears are simply small, hidden holes without a flap or other external covering. Male dolphins are generally larger than females, and the length can range from 6-13 feet (2-4 meters), weighing anywhere from 200-1400 pounds (90-650 kg).

Bottlenose Dolphins are carnivorous predators and will eat fish, squid, and shrimp, depending on what is available. Their teeth are interesting in that they lock together and are, therefore, not made for chewing. Instead, they use their teeth to grasp their food, and they swallow fish whole. If a fish is too large to swallow whole, the dolphin will shake it or scrape it against the ocean floor or another object to break it apart. To keep the bones from getting caught or puncturing the dolphin’s throat, fish are always eaten head first. They will also often hunt in groups, herding the fish to catch them.

Interesting Fact: Bottlenose Dolphins that live in deeper, open waters have been seen herding schools of fish by swimming around the school in a tightening circle. They will slap the fish with their tailfins, which stuns them, and then, once the school of fish is gathered in a tight ball, they will take turns swimming through the ball and feeding.

Female Bottlenose Dolphins reach sexual maturity at between 5 and 12 years of age and males 10-12 years old. Sexual maturity appears to be directly linked with body size. Females are mature once they have reached a length of 7.5 feet (2.3 meters), and the males are mature at 8-8.5 feet long (2.4-2.6 meters). Mating can occur at any time of year, and the gestational period is about 12 months. During birth, which occurs underwater, another dolphin, often called an “auntie dolphin” will be present to help. The dolphin calf will nurse for about 18 months and will swim very close to the mother, using her momentum to move it along. During the first few days after birth, the mother will continually whistle to the calf, and this helps the calf to identify its mother.

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Bibliography:
Bottlenose Dolphin. Encarta Encyclopedia, © 2000.
Cetacea: Tursiops truncatus (Bottlenose Dolphin). Accessed 08/20/04 at http://www.cetacea.org/bottle.htm
Bottlenose Dolphins. Accessed 08/20/04 at http://www.seaworld.org/infobooks/Bottlenose/.
ACS Bottlenose Dolphin Cetacean Fact Sheet. Accessed 08/20/04 at http://www.acsonline.org/factpack/btlnose.htm.