Habitat & Distribution - Bottlenose Dolphins

DISTRIBUTION

1. Bottlenose dolphins live in temperate and tropical waters worldwide. Distribution is generally limited to surface water temperatures of 10° to 32°C (50°-90° F). Documented sightings of bottlenose dolphins are indicated in dark blue. 2. In the Pacific Ocean, bottlenose dolphins are found from northern Japan to Australia and from Southern California to Chile. They are also found offshore in the eastern tropical Pacific as far west as the Hawaiian Islands. Off the California coast bottlenose dolphins have been observed as far north as Monterey, particularly during years of unusual warmth. 3. In the Atlantic Ocean, bottlenose dolphins are found from Nova Scotia to Patagonia and from Norway to the tip of South Africa. They are the most abundant dolphin species along the United States coast from Cape Cod through the Gulf of Mexico. 4. Bottlenose dolphins are also found in the Mediterranean and Black Seas. 5. Indo-Pacific bottlenose dolphins are found in the Indian Ocean from Indonesia to Australia to South Africa, the Red Sea, and in the tropical and subtropical waters of the western Pacific.

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HABITAT

1. Bottlenose dolphins live in a variety of habitats, from coastal waters to the open ocean. 2. Scientists recognize two bottlenose dolphin ecotypes (forms): coastal and offshore. In the northwest Atlantic, bottlenose dolphin coastal and offshore ecotypes can be differentiated by skull and body measurements as well as by characteristics of their blood. • In general, the coastal ecotype seems to be adapted for warm, shallow waters. Its smaller body and larger flippers suggest increased maneuverability and heat dissipation. These dolphins frequent harbors, bays, lagoons, and estuaries. • In general, the offshore ecotype seems to be adapted for cooler, deeper waters. Certain characteristics of its blood indicate that this form may be better suited for deep diving. Its larger body helps to conserve heat and defend itself against predators. • In northwest Atlantic bottlenose dolphin studies, researchers determined that dolphins within 7.5 km (4.65 mi) of shore were coastal ecotypes. Dolphins beyond 34 km (21 mi) from shore were offshore ecotypes.

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MIGRATION

1. Variations in water temperature, movements of food fish, and feeding habits may account for the seasonal movements of some dolphins to and from certain areas. 2. Some coastal dolphins in higher latitudes show a clear tendency toward seasonal migrations, traveling farther south in the winter. For example, coastal bottlenose dolphins on the Atlantic side of the U.S. migrate seasonally between New Jersey and North Carolina. 3. Coastal dolphins in warmer waters show less extensive, localized seasonal movements. 4. Some coastal animals stay within a limited home range: an area in which individuals or groups regularly move about during day-to-day activities. • Individual dolphins that live within a home range are called "local residents." Resident dolphins have been identified along the coasts of Georgia, Florida, Texas, southern California, Gulf of California, and South Africa. • Groups of dolphins that reside within a home range make up "resident communities." The Sarasota, Florida resident dolphin community home range is an area of about 125 km2 (48.3 mi2). • Home ranges may overlap.

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POPULATION

1. Bottlenose dolphins are not endangered. 2. The worldwide population of bottlenose dolphins is unknown. Specific bottlenose dolphin populations in a few areas have been estimated. • U.S. National Marine Fisheries Service (NMFS) surveys estimate 243,500 bottlenose dolphins in the eastern tropical Pacific. • Japanese surveys estimate 316,935 dolphins in the northwest Pacific. • NMFS surveys in the northern Gulf of Mexico estimate as many as 45,000 bottlenose dolphins from the coast to about 250 km (155 mi.) offshore. This area includes the Gulf's bays and sounds, coastal waters (about 17,600 individuals), and continental shelf waters (about 25,320 individuals). • In U.S. waters of the western North Atlantic, average abundance estimates for the coastal population are 9,206 from the summer survey and 19,459 from the winter survey. The western North Atlantic average abundance estimate for the offshore population is 29,774 individuals. • The Mediterranean population is estimated at less than 10,000. • Average abundance estimates for the U.S. west coast include the California coastal population of 206 individuals and the California-Oregon-Washington offshore population of 5,065 individuals. • Chromosome banding techniques have proven useful in bottlenose dolphin population studies. In some areas, scientists can identify individuals and determine relationships among dolphins in a group.