Dolphin Habitat and Distribution

A. Distribution (Leatherwood and Reeves, 1983).

1. Bottlenose dolphins inhabit temperate and tropical waters throughout the world.
   
2. In the Pacific Ocean, bottlenose dolphins are found from northern Japan and California to Australia and Chile. They are also found offshore in the eastern tropical Pacific as far west as teh Hawaiian islands. Off the California coast bottlenose dolphins have been observed as far north as Monterey, particularly during years of unusual warmth (Wells, et al., 1990).
   
3. In the Atlantic Ocean, bottlenose dolphins are found from Nova Scotia and Norway to Patagonia and the tip of South Africa. They are the most abundant dolphin species along the United States from Cape Cod through the Gulf of Mexico.
   
4. Bottlenose dolphins are also found in the Mediterranean Sea, and in the Indian Ocean from Australia to South Africa.

B. Habitat.

1. Bottlenose dolphins inhabit the pelagic zone as well as harbors, bays, lagoons, gulfs, and estuaries.2. In the northwest Atlantic, there seem to be at least two ecotypes (forms) of the bottlenose dolphin. They can be differentiated by skull and body measurements as well as by characteristics of their blood (Hersh and Duffield, 1990).

   a) In general, the coastal ecotype seems to be adapted for warm, shallow waters. Its smaller body and larger flippers suggest increased maneuferability and heat dissipation (Hersh and Duffield, 1990). These dolphins frequent harbors, bays, lagoons, and estuaries.

   b) In general, the offshore ecotype seems to be adapted for cooler, deeper waters. Certain characteristics of their blood indicate that this form may be better suited for deep diving. Its larger body helps to conserve heat and defend itself against predators (Hersh and Duffield, 1990).

C. Migration.

1. Variations in water temperature, migration of food fish, and feeding habits may account for the seasonal movements of some dolphins to and from certain areas (Duffield and Chamerlin-Lea, 1990; Shane, et al., 1986).
   
2. Some coastal dolphins in higher latitudes show a clear tendency toward seasonal migrations, traveling further south in the winter. Those in warmer waters show less extensive, localized seasonal movements (Shane, et al., 1986).
   
3. Some coastal animals stay within a limited home range (an area in which individuals or groups regularly move about during day-to-day activities). Home ranges may overlap (Duffield and Chamberlin-Lea, 1990; Wells and Scott, 1991).Most dolphins undergo seasonal movements, probably as a response to variations in water temperature and food availability.
   (Photo by Rrandall S. Wells.)

D. Population.

1. The worldwide population of bottlenose dolphins is unknown. Specific bottlenose dolphin populations in a few areas have been estimated.
   
   a) In the United States Gulf of Mexico, their numbers are estimated to be at least 67,000 (Blaylock, et al., 1995).
   
   b) The populations found in the western North Pacific and along Japanese coasts are estimated at about 35,000 (Klinowska, 1991).
   
   c) In U.S. waters of the western North Atlantic, the bottlenose population is estimated at about 11,700. Of course, at least 9,200 are offshore animals (Blaylock, et al., 1995).
   
   d) The Mediterranean population is estimated at less than 10,000 (Klinowska, 1991).
   
2. Bottlenose dolphins are not endangered.
   
3. Chromosome banding techniques have proven useful in bottlenose dolphin population studies. Scientists can identify individuals and determine relationships among dolphins in a group (Duffield and Chamberlin-Lea, 1990).

Bibliography