Bottlenose Dolphin

Scientific Classification

Common Name

bottlenose dolphin, Atlantic bottlenose dolphin, Pacific bottlenose dolphin, bottle-nosed dolphin

Kingdom

Animalia

Phylum

Chordata

Class

Mammalia

Order

Cetacea

Suborder

Odontoceti

Family

Delphinidae

Genus Species

Tursiops truncatus

Fast Facts

Description

Bottlenose dolphins are light to dark gray over their dorsal surface, fading into a white or cream along their ventral region. They have a streamlined fusiform body shape. The source of their common name, bottlenose dolphins exhibit a pronounced anterior rostrum (often referred to as a beak), typically 7 to 8 cm (3 in.) in length. Said rostrum generally contains 72 to 104 conically-shaped, homogenous teeth, with tooth counts varying among individuals. Their dorsal fin is falcate.

It should be noted that two distinct ecotypes are recognized. The coastal ecotype typically exhibits smaller average body size with relatively larger flipper size. Comparatively, the offshore ecotype typically exhibit larger average body size and darker coloration, among other morphological distinctions.

Size

Coastal ecotype: average 2.5 to 2.7 m (8.2 to 8.9 ft.)
Offshore ecotype: 3.7 m (12 ft.)

Atlantic bottlenose dolphins as a whole are typically smaller than Pacific bottlenose dolphins; however, bottlenose dolphins frequenting cooler, temperate waters in either ocean tend to exhibit sizes indicative of the relatively larger offshore ecotype.

Calves are approximately 111 to 116.3 cm (43.7 to 45.7 in.) long at birth.

Male: Males may be slightly larger than females

Weight

Coastal ecotype: average 190 to 260 kg (419 to 573 lbs.)
Offshore ecotype:  average 454 kg (1,000 lbs.); maximum 650 kg (1,433 lbs.)

Newborn calves weigh approximately 20 kg (44 lbs.)

Male: Physically mature males tend to be more massive than physically mature females

Diet

Dolphins are active predators and eat a wide variety of fishes, squids, and crustaceans such as shrimps. The diet of coastal bottlenose dolphins is diverse and depends upon geographical location. Many dolphins eat only fish, although some also eat small numbers of cephalopods, crustaceans, small rays, and sharks.

Gestation

Approximately 12 months

Estral Period

Roughly 12 month anestrus followed by an approximate 12 month polyestrus consisting of at least 3 distinct cycles, all of which are typically focused in the late spring. There is little to no indication of senescence (menopause) in the female bottlenose dolphin. Successful births and rearing have been witnessed up through 48 years of age in the Sarasota dolphin population.

Nursing Duration

A calf may nurse for up to 18 to 24 months. The maximum nursing period observed was seven years in Sarasota Bay, Florida, and may serve as a bonding activity.

Sexual Maturity

Typically exhibited as a function of age-dependent body size

Male: become sexually mature at about 10 to 13 years and 2.4 to 2.6 m (8 to 8.5 ft). In the wild, males in Sarasota Bay reach sexual maturity between the ages of 8 and 13 years.
Female: have been known to reach sexual maturity from 5 to 13 years old. In Florida waters, the average female is sexually mature at about 5 to 12 years and 2.2 to 2.3 m (7.2 to 7.6 ft).  The average age at which bottlenose dolphin females in Sarasota Bay have their first offspring is 8 to 10 years. 

Life Span

Survival rates have been increasing in marine mammal parks and aquariums, with the most recent study showing an annual survival rate of 0.97 (which means 97% of the population is expected to survive from one year to the next) for dolphins in U.S. facilities. This corresponds to a median life span of 22.8 years.

Survival rates reported for wild populations have varied widely, from .902 to .961, with median life spans between 8.3 and 17.4 years. These differences may be due to differences in study methodology (i.e., tracking a live population vs determining the age of dead animals that stranded), or may reflect true lifespan variations in different wild populations.

The oldest living U.S. dolphin in human care was born February 27, 1953, at Marineland of Florida (now the Dolphin Conservation Center at Marineland, St. Augustine, Florida). Nellie the dolphin passed away at Marineland on April 30, 2014. She was 61 years old.

The Sarasota Dolphin Research Program has studied dolphins in Sarasota Bay, Florida, since 1970 and is the longest running study of a wild dolphin population in the world. Based on this study, the oldest bottlenose dolphin is Nicklo, who was 67 years old when she was last sighted in 2017 in the Sarasota Bay population. Researchers extracted a tooth from her in 1984 to determine her age.

Range

Temperate and tropical marine waters worldwide; distribution is generally limited to surface water temperatures of 10° to 32°C (50° to 90°F).
In the Pacific, they are found from northern Japan to Australia and from southern California to Chile; In the Atlantic, they are found from Nova Scotia to Patagonia and from Norway to the tip of South Africa; In the Indian Ocean, they are found from Australia to South Africa.
Bottlenose dolphins are also found in the Mediterranean and Black Seas. 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.

Habitat

Bottlenose dolphins inhabit warm temperate waters, adapting to several marine and estuarine habitats, including, occasionally, rivers. Habitat use is influenced by environmental heterogeneity; meaning these animals distribute through an ecosystem depending on factors like resources, depth, water temperature, sea-bed gradient and type of sediment.

Population

Global: The worldwide population of common bottlenose dolphins is about 600,000. Indo-Pacific bottlenose dolphins are abundant, but the overall population is unknown.

Status 

IUCN: Least Concern
CITES: Appendix II
USFWS: Protected in U.S. waters by the Marine Mammal Protection Act of 1972; not considered endangered or threatened

Fun Facts

1. Dolphins frequently ride the bow wake or the stern wake of boats. They have been seen jumping as high as 4.9 m (16 ft.) out of the water and landing on their backs or sides, in a behavior called a breach.
2. Both young and old dolphins chase one another, carry objects around, toss seaweed to one another, and use objects to invite each other to interact. Such activity may be practice for catching food.
3. Adults eat approximately 5% of their body weight per day. Bottlenose dolphins often cooperate when hunting and catching fish. In open waters, a dolphin pod sometimes encircles a large school of fish and herds them into a tight ball for easy feeding. Then the dolphins take turns charging through the school to feed. Occasionally dolphins will herd fish to shallow water where they are easy prey.
4. Bottlenose dolphins generally do not need to dive very deeply to catch food. Depending on habitat, most bottlenose dolphins regularly dive to depths of 3 to 46 m (10 to 150 ft.). They are, however, capable of diving to some depth. Under experimental conditions, a trained dolphin dove 547 m (1,795 ft).
5. In the past, bottlenose dolphin groups have been referred to as pods, social groups of unchanging composition. More recently, long-term studies of bottlenose dolphins have now shown that their group composition changes. Coastal bottlenose dolphins are primarily found in groups of 2 to 15 individuals. The associations of the animals are fluid, often repeated but not constant. Solitary coastal animals are observed in various regions of the world.
6. The dolphin's sleek, fusiform body, together with its flippers, flukes, and dorsal fin, adapt this animal for ocean life. A dolphin's forelimbs are pectoral flippers. As it swims, a dolphin uses its pectoral flippers to steer and, with the help of the flukes, to stop.
7. Bottlenose dolphins routinely swim at speeds of about 5 to 11 kph (3 to 7 mph).
8. The maximum voluntary breath hold recorded for a coastal bottlenose dolphin was 7 minutes 15 seconds The maximum breath hold duration registered for a tagged off-shore bottlenose dolphin was 14 minutes.
9. In the wild, group composition and structure are based largely on age, sex, reproductive condition, family relationships and association histories.
10. Adults eat approximately 5% of their body weight per day. Bottlenose dolphins often cooperate when hunting and catching fish. In open waters, a dolphin group sometimes encircles a large school of fish and herds them into a tight, dense mass for easy feeding. The dolphins take turns charging through the school to feed while the others keep the fish from scattering. Occasionally dolphins herd fish to shallow water and trap them against a shore or sandbar.
11. For more information about bottlenose dolphins, explore the Bottlenose Dolphin InfoBook.
    
     

Ecology and Conservation

Dolphins are important predators of fish, crustaceans, and other marine fauna. They have been hunted in many parts of the world for meat and other by-products made from dolphin parts (such as fertilizer, and machinery lubricants made from their jaw oil). Possessing a larger brain than a human's, dolphins show a high degree of certain types of intelligence, making them popular subjects for research in fields such as cetacean physiology, psychology, and sociology. Their capacity for learning has also made them ideal trained performers in oceanarium and zoological shows.

Under the Marine Mammal Act of 1972, the taking of dolphins requires a special permit. Bottlenose dolphin populations were drastically reduced around the turn of the last century due to commercial fishing operations. Today, fishing gear and nets can accidentally entangle, injure or drown dolphins. Dolphins, particularly coastal animals, are also affected by heavy boat traffic, habitat loss and pollution. Industrial and agricultural pollutants (including pesticides, herbicides and fire retardants) often enter coastal habitats through runoff, resulting in high levels of toxins both in the water and in dolphin tissues. 

Not only is it illegal, but it also may be dangerous to approach a wild dolphin. Marine parks like SeaWorld and Discovery Cove provide a safe environment for humans to interact with dolphins.

Bibliography

Byrum, Jody and Nuzzolo, Deborah. Bottlenose Dolphins. Third Edition. SeaWorld Education Department, 1996.

Jefferson, T.J. Leatherwood, S. and M.A. Webber. FAO Species Identification Guide. Marine Mammals of the World. Rome. FAO, 1993.

Leatherwood, Stephen, and Reeves, Randall R. The Sierra Club Handbook of Whales and Dolphins. San Francisco: Sierra Club Books, 1983.

Nowak, Ronald M. (ed.). Walkers Mammals of the World. Vol. II. Baltimore: Johns Hopkins University Press, 1991.

Nuzzulo, Debrorah. Dolphin Discovery: Bottlenose Dolphin Training and Interaction. SeaWorld Education Department Publication, SeaWorld, Inc., 2003.

Parker, S. (ed.). Grizmeks Encyclopedia of Mammals. Vol. IV. New York: McGraw-Hill Publishing Co., 1990.

Reeves, R. R., Stewart, B.S., Clapman, P.J., and J.A. Powell (Peter Folkens illustrator). National Audubon Society: Guide to Marine Mammals of the World. New York: Random House, 2002.

http://animaldiversity.ummz.umich.edu