San Francisco State University
Department of Geography

Geography 316:  Biogeography

The Biogeography of 
Bottlenose Dolphin(Tursiops truncatus)

(Sylvestre 1993)
 

by Brandon Cadelinia, student in Geography 316, Fall 1999

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Ceatacea (whales/dolphins)
Suborder: Odontoceti (toothed whales)
Family: Delphinidae
Genus: Tursiops
Species: Tursiops truncatus

Description of Species:

     The head and body length of a Tursiops truncatus is 175-400 cm with pectoral fin length of 30-50cm.  Dorsal fin height averages about 23 cm and it’s tail flukes’ width is approximately 60 cm.  Average weight is usually 150-200 kg and has been reported to weigh in excess of 650 kg (Nowak, 1991).
     It’s body is slender with a convex melon.  The snout is short, wide, and well defined.  The upper jaw is shorter than the lower.  The dorsal fin is median, high, and falcate.  The pectoral fins are relatively short and falcate.  Pronounced median notches are present on the flukes.  Each side of both jaws consists of 18-26 small convex-shaped teeth.  It has a medium to dark colored back, light gray flanks, and pink or white stomach (Sylvestre, 1993).

Distribution:

     The bottlenose dolphin (Tursiops truncatus) is geographically located in areas of temperate and tropical waters around the world.  The consensus is that there is one species of tursiops worldwide, separated into geographical races (Shane, Wells, Wursig, 1986).  These “geographical races” are distributed within three main areas: 1) temperate and tropical waters of the Atlantic Ocean and adjoining seas (Nowak, 1991) – the bottlenose dolphin has been known to swim from CapeCod through the Gulf of Mexico as well as swimming from Patagonia and South Africa to Norway and Nova Scotia (Sea World, 1996), 2) Eastern Pacific Ocean and the Gulf of Mexico and 3) Temperate and tropical waters of the Indian, South Pacific, and western and southern North Pacific oceans and adjoining seas (Nowak ,1991).
    Due to the mobility of the bottlenose dolphins, “we can only make educated guesses about what makes them choose one area over another” (Haley, 1978).  The mobility of the bottlenose dolphin has resulted in various ecotypes suiting their way of life.  According to Haley (1978), “all are remarkably adapted to live in the ocean and to exploit various portions of the ocean environment.”
     According to Nowak (1991), “Many researchers recognize two forms of tursiops, the smaller staying in shallow waters near the main land and the larger occurring farther offshore.”  They can be differentiated by skull and body measurements as well as by characteristics of their blood (Sea World, 1996).  The coastal ecotype seems to be adapted for warm, shallow waters.  Its smaller body and larger flippers suggest increased maneuverability and heat dissipation (Sea World, 1996).  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 (Sea World, 1996).
     In the quantitative study of Ballance (1992), the author concluded that data on relative numbers, distribution patterns, behavior and diet indicate that this is a general trend in habitat use.  Her research was conducted during the spring, summer, and fall of 1984, along the west coast of mainland Mexico in the Gulf of California.  In terms of habitat use patterns, dolphins were generally sited in shallow, turbid waters where the bottom was composed of sand (Balance 1992).  Dolphin sighting rate and number of schools were the highest in areas near the mouth of estuaries, in which they utilized as feeding places (Balance, 1992).  Estuarine areas repeatedly have been found to be sites of high dolphin occurrence along the U.S. coast of the Gulf of Mexico preferred areas include ship channels, passes b inshore bays and the open ocean, river mouths, bays, lagoons, and estuarine complexes (Balance, 1991).  In conclusion, Balance (1991) suggests that further research down of residence patterns of bottlenose dolphin in deferring habitat types with temporary due in search of food.
 

Map of Distribution:(Cavendish 1997)

Natural History:

HOME RANGE
     A home range is an area regularly used by an individual or group in the course of performing normal daily activities (Shane, Wells, Wursig 1986).   In the review of literature conducted by Shane, Wells, and Wursig (1986), the ecology, behavior and social organization of the bottlenose dolphin were discussed.  According to Shane et al.:
    The first indication that T. truncatus had a home range was provided by Caldwell (1955), who defined a minimum home range for a recognizable individual dolphin in Florida.  Caldewell and Golley (1965) estimated a minimum home range of “95 miles” for an albino bottlenose dolphin in Georgia and South Carolina…Caldwell and Caldwell (1972a) propose that the species may have seasonal home ranges linked by a traveling range” (35).

ECOLOGY AND BEHAVIOR
     Scott et al. (1990) suggested that these seasonal home ranges were the result of three factors that may influence the distribution shifts: 1) seasonal change in prey distribution, 2) predation pressure, and 3) reproductive requirements.  Dolphins shift their distribution in response to the migration of the mullet, their primary prey (Scott et al., 1990).  As survival instincts dolphins engage in two behaviors: 1) avoidance of sharks in the inshore waters of the Gulf of Mexico during the summer and populating protected waters of the bay, and 2) mothers seeking out sheltered areas in the spring to protect their vulnerable calves.

ADAPTATIONS
     During a dive, the Tursiops truncatus undergoes physiological adaptations to conserve oxygen while underwater.  As with all other mammals, the heartbeat slows down.  Blood is also shunted away from tissues that can tolerate low oxygen levels and is perfused to major body organs such as heart, lungs, and brain.  A high content of the oxygen binding-protein, known as myoglobin, is contained within the muscles, allowing for storage of oxygen, thus preventing muscle oxygen depletion (Sea World, 1996)
     In the process of respiration, the dolphin breathes through a single blowhole on the dorsal surface of its head.  It’s average respiratory rate is about two to three breathes per minute. This process involves the three following steps: 1) The dolphin holds it’s breath while underwater; 2) It opens its blowhole and begins to exhale just before reaching the surface of the water; and 3) At the surface, the dolphin quickly inhales and relaxes the muscular flap to close it.  One breathing cycle has a duration of about 0.3 seconds.  At each respiration, a dolphin exchanges 80% or more of its lung air.  This percent is much more efficient than humans, considering that only about 17% of their lung air is exchanged with each breath (Sea World, 1996).
     The thermoregulatory of the bottlenose dolphin is quite an interesting system.  It’s core temperature is about 36.90C (98.4’F).  Most of their body fat is deposited into a thick layer of blubber located just underneath the skin.  This layer functions as an insulator that streamlines the body and serves as an energy reserve.  Body fat generally accounts for about 18% to 20% of it’s body weight (Sea World, 1996).
      A combination of a fusiform shape and reduced limb size decreases the amount of surface area exposed to the external environment.  These essential features conserve body heat.  As result, dolphins of larger body size and smaller flippers usually adapt to cooler and deeper waters than do coastal dolphins (Sea World, 1996).
     The final contributor to this system of regulation is the dolphin’s circulatory system.  As with the human body, the circulatory system adjusts blood flow to conserve or dissipate body heat and maintain body temperature.  Heat from arterial blood is transferred to venous blood rather to the environment.  This countercurrent heat exchange aids dolphins in conservation of body heat.  In addition to this heat exchange, body heat is also conserved by the shunting of  blood away from the surface of the body, leading to a decrease in blood circulation.  Finally, when a dolphin needs to dissipate body heat, the opposite process occurs.  Rather than countercurrent heat exchange, circulation increases to the peripheral veins of the dolphin’s flippers, flukes, and dorsal fins.  Then, there is a decrease of circulation to veins returning blood to the body core. The final result is the release of body heat into the environment (Sea World, 1996).

DIET AND FEEDING BEHAVIOR
     Shane (1990) observed the various types of fishes that the Tursiops truncatus preyed upon.  Fish size ranged from approximately 2.5 cm- 1 m long.  Shane identified the following species of fishes: 1) needlefish, 2)striped mullet, and 3) catfish.  Tentatively, she also identified jack crevalle, Florida pompano, pinfish, lizard fish, mackerel, and southern flounder.  Barros and Odell (1990) discovered that sand trout, mullet, and silver pouch, were the most common preys after analyzing stomach contents of bottlenose dolphins stranded in southwest Florida.
     After observing the feeding behavior of bottlenose dolphins, Shane (1990) came to several interpretations.  Dolphins commonly dove in varying directions in one area, making fluke-up dives or tail-stock dives.  Dolphins engaged in “against-current feeding”, in which they faced against a strong tidal current and stayed in one area.  This behavior was commonly found under Causeway bridges where there was an abundant number of fish.  The dolphins would engage in a “horizontal circle feeding” or a “vertical circle feeding”.  In the horizontal position, the dolphin positioned it’s body bent forward as it swam rapidly in a circle.  While in this position it pursued fish located just a few centimeters ahead of it’s rostrum.  In the vertical position, the dolphin vertically positioned itself in the water with it’s head up.  While in this position, the dolphin would swing it’s head repeatedly, in a 360 degree arc as it pursued small fish at the tip of it’s rostrum just beneath the surface.
     During a “feeding rush”, a dolphin would suddenly increase it’s speed for 10-20 m as it headed toward a shoreline.  As the dolphin neared the shore, it would lean on it’s side, spin in a circle, and catch it’s prey.  “Fish kicking” involved the dolphin using it’s tail flukes and or stock to kick a fish near the water’s surface high into the air.  Fishes were kicked at distances ranging about 1.2-9.2 m high and 0-9.2 m forward.  When the wounded fish landed, the dolphin would swim to it’s prey and usually consume it alone.  Mullets or spotted seatrout were often identified as the prey.
     Shane (1990) concluded that there was scant observation of cooperative feeding but that cooperation was possible.  She also summarized that feeding behavior depended on location of prey in the water column, the size of the fish, the depth of the water, the physical barriers against which fish could be trapped, and other unknown factors.

REPRODUCTION AND MATING
     Male sexual maturity begins between 10-12 years old.  Female sexual maturity begins between 5-12 years old.    The female gives birth every 2-3 years.  Gestation last for a year and birth occurs from February to May and from September to November, off the coast of Florida.  Birth occurs during midsummer in the European waters.  Lactation lasts 12 to 18 months.  Life span is estimated at 35 years or more (Sylvestre, 1993).  In the study of Scott et al. (1990), relatively large testes indicated a promiscuous mating system.  Scarred bodies of older males were indicative of polygynous systems and male-male competition.

Evolution:

    Dolphins, porposies, and whales belong to the Cetacean order.  The order Cetacean is further divided in two types known as the Odontoceti, or toothed whales, and the Mysticeti, or baleen whales. [Figure 2]
Dolphins are members of the Odontoceti, which use their teeth to capture their prey.  Dolphins are also characterized according to their relative habitat: oceanic, coastal, and river.  The bottlenose dolphin falls into the oceanic family, which is comprised of thirty-four species. [Figure 2]
It has been concluded that dolphins, porpoises, and whales evolved from Mesonychilds, a group of land-loving carnivores.  They have been estimated to have lived 60 and 35 million years ago (Cavendish, 1997).  These mammals eventually explored the sea, resulting in morphological and physiological changes of their bodies to suit their newly discovered habitat.
The Pakicetus was recognized as the oldest cetacean, who resembled a large otter (Cavendish, 1997).  This creature was estimated to have lived 50 million years ago.  The Pakicetus may have undergone some adaptations to suit marine life such as short, paddle-shaped limbs.
 It was about 30 million years ago that these early ancestors of the Ceatacean order began to resemble the present-day order.  These early ancestors had to experience a great amount of internal and external bodily changes to function and survive in their new marine habitat.  Fortunately, these changes occurred at a rapid speed relative to evolutionary terms.  Limbs disappeared and flippers and a tail replaced them.  The skeleton grew long enough to support the two flukes.  The body was able to travel through the water much quicker due to skin alteration and the streamlined quality of the body.

[Figure 2]

(Cavendish 1997)
 

Bibliography

Balance, Lisa Taylor.  “Habitat use Patterns and Ranges of the Bottlenose Dolphin in the Gulf of California, Mexico,” Marine Mammal Science 8(3), 1992,                 pp.262-274

Barnes, Lawrence G.  “The Fossil Record and Evolutionary Relationships of the Genus Tursiops,” In The Bottlenose Dolphin, edited by Stephen Leatherwood and                Randall R. Reeves, pp3-28. San Diego: Academic Press, Inc., 1990.

Barros, Nglio B. and Daniel K. Odell.  “Food Habits of Bottlenose Dolphins in the Southeastern United States,” In The Bottlenose Dolphin, edited by Stephen              Leatherwood and Randall R. Reeves, pp.309-328. San Diego: Academic Press, Inc., 1990.

Bloom, P, A. Goodson, M. Klinowska and C. Sturtivant.  “The Activities of a Wild, Solitary Bottlenose Dolphin,”  Aquatic Mammals 21(1), 1995, pp.19-42

Bottlenose Dolphins. [Online]. Available: http://www.seaworld.org/bottlenose_dolphin/bottlenose_dolphins.html

Cavendish, Marshall.  Encyclopedia of  Mammals.  New York, London, Toronto and Sydney. Vol.5, 1997. Dog-Gal

Cousteau, Jacques-Yues and Philippe Diole.  Dolphins.  Doubleday and Company, Inc. Garden City, New York, 1975.

Haley, Delphie, ed.  Marine Mammals of Eastern North Pacific and Artic Waters.  Pacific Search Press. 1978.

Hersh, Sandra L. and Deborah A. Duffield.  “Distinction Between Northwest Atlantic Offshore and Coastal Bottlenose Dolphins Based on Hemoglobin Profile and              Morphometry,” In The Bottlenose Dolphin, edited by Stephen Leatherwood and Randall R. Reeves, pp129-139.  San Diego: Academic Press, Inc., 1990.

Leatherwood, S and Randall R. Reeves [eds].  The Bottlenose Dolphin.  San Diego: Academic Press, Inc., 1990. i-xviii, 1-653.

LeBoeuf, Nicole.  Species Corner: Bottlenose Dolphins. [Online].  Available: http://www.tmmsn.org/mmgulf/tursiops.html

May, John.  The Greenpeace Book of Dolphins.  Sterling Publishing Co., Inc. New York, 1990.

Nowak, Ronald M.  Walker’s Mammals of the World.  The Johns Hopkins University Press, Baltimore & London, 1991.  5th edition, Vol.II.

Shane, Susan H.  “Ecology, Behavior and Social organization of the Bottlenose Dolphin: A Review,” In The Bottlenose Dolphin, edited by Stephen Leatherwood              and Randall R. Reeves, pp34-63.  San Diego: Academic Press, Inc., 1990.

Scott, M.D., R. Wells and A. Irvine.  “A long-term study of Bottlenose Dolphins on the east coast of Florida,” In The Bottlenose Dolphin, edited by Stephen                 Leatherwood and Randall R. Reeves, pp 235-244.  San Diego: Academic Press, Inc., 1990.

Sylvestre, Jean-Pierre.  Dolphins and Porpoises.  Sterling Publishing Co. Inc. New York, 1993.
 
 

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