Dive Dry with Dr. Bill

078: Bottlenose Dolphin

The famous television star "Flipper" was a member of this species. Bottlenose dolphins may reach 12 feet and 1,400 pounds although most are smaller than this. Males are larger than females. Their bodies are light to slate gray on top and lighter on the sides and belly, which may also be spotted. They have a distinctive beak extending from their rounded head. The dorsal fin is high and curved, or sickle-shaped. Their size and shape of the dorsal fin make them fairly easy to identify. Their maximum life span is estimated at 25-30 years.

Bottlenose dolphins live in coastal and inshore waters worldwide in temperate and tropical areas. They may be observed in harbors, bays and other partially enclosed bodies of water. Some researchers feel there are two types: one living close to the coast and the other further offshore. Different groups may remain in one area, or migrate between different areas. They may live in different areas during different stages such as breeding or giving birth.

Bottlenose dolphins are members of the toothed whales. This species has 18-26 pairs of sharp, pointed teeth in their upper and lower jaws. They feed primarily on fish and squid near the surface or octopi near the bottom in shallower waters. They can coordinate their fishing activities or sometimes chase fish onto to shore to catch them. An adult may eat 15-30 pounds of food a day (that requires quite a plate). They are able to dive to depths in excess of 1,000 feet. Predators on this species include sharks (tiger, dusky and bull) as well as killer whales.

Bottlenose dolphins are social animals. Those living near the coast are usually in small groups or pods of 12-20 members. Offshore they may form groups of several hundred. Individuals may move freely from one pod to another. At times these smaller pods may join others forming aggregations of hundreds of individuals. Behaviors that interest humans include their ability to leap as high as 20 feet and "bow riding" on the pressure wave created by the bow of boats and ships. It is believed that bow riding may originate from dolphins swimming in the bow wakes of large whales before large, fast boats came along.

Females are sexually mature at 5-7 years while males (as usual) mature later at about 11 years. The gestation period is about 12 months and calves are born year-round. The young animals nurse for 12-18 months and remain with their mothers for up to three years to learn fishing and other behaviors.

Like other mammals, dolphins must breathe air at the surface through their single blowhole at the top of the head. They can hold their breathe for several minutes but generally breathe more frequently. When exhaling, they create a single, explosive blow.

Since these dolphins are constantly active, one might ask "when do they sleep?" They actually have several different resting modes used for a total of about eight hours a day. One is especially interesting. The bottlenose dolphin shuts down one half of its brain, along with the opposite eye. The sleeping side maintains a low level of alertness while the other side remains aware to watch for predators, to navigate or control breathing. The roles are reversed after about two hours. Of course some humans I know go this one step further... they shut off both sides of their brains, often permanently!

This species is protected in US waters by the Marine Mammal Protection Act. Formerly they were incidental bycatch in gill nets, tuna purse seiners and shrimp trawlers although advances in fishing technology have eliminated some of this threat. In the past they have been hunted by other cultures, most notably in the Black Sea by the Russians and Turks. They are also hunted in the West Indies, West Africa, Japan and other areas. Based on autopsies of animals in large die-offs, they are subject to viral infections that can kill many. Researchers believe mortality due to these viruses may be increased by the presence of PCB pollutants in their tissues.

© 2004 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Skull of bottlenose dolphin found on a beach near Mexico's Bahia Magdalena; large teeth of the
bottlenose which captures larger schooling fish than the common dolphin;
bottlenose dolphins in the waters of Magdalena Bay.

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia