Tursiopsbottlenose dolphin

Diversity

Tursiops, bottlenose dolphins, are diverse genetically, morphologically, and in life histories based on habitat (Chen et al., 2017). The taxonomy is not fully resolved for the genus (Chen et al., 2017; Costa et al., 2016). It is in the family Delphinidae and currently includes at least three species. Two species occupy the western North Pacific, T. aduncus and T. truncatus. Tursiops truncatus and the subspecies Tursiops truncatus gephyreus are found in the western South Atlantic (Costa et al., 2016). Tursiops truncates, found in offshore waters, have a pale-grey blaze that indents a darker grey dorsal cape towards the basis of the dorsal fin; those individuals are found in pods of up to about 30 individuals. Tursiops aduncus, found in inshore waters in pods comprised of 2-10 individuals, do not exhibit those marks. Other differences in external appearance between the species include rostrum length, body size, ratios of rostrum length to body length and snout-to-eye length (Borsa, Andrefouet, and Juncker, 2012). (Borsa, et al., 2012; Chen, et al., 2017; Costa, et al., 2016)

Geographic Range

Bottlenose dolphins are found in tropical to temperate marine waters. This includes the coasts of all major continents and many islands, shallow offshore banks and in open waters (Chen et al., 2017). (Chen, et al., 2017)

Habitat

Bottlenose dolphins are found in a wide range of habitats. They mostly occupy coastal areas, but can also be found in estuarine systems, as well as pelagic areas (Grazia Pennino et al., 2017; Milmann et al., 2017). Occasionally, they can also be found in rivers (Wells and Scott, 1999). (Grazia Pennino, et al., 2017; Milmann, et al., 2017; Wells and Scott, 1999)

Physical Description

Bottlenose dolphins, Tursiops, have a fusiform body shape, with flippers, dorsal fin, and beak. Rostrum length is longer in offshore populations than in coastal populations. Sexual dimorphism appears in offshore populations as well. Males tend to be bigger with an average total body mass of 253kg compared to the female average of 210kg (Mallette et al., 2016). Offshore populations tend to have a smaller overall body length, with an average of about 310cm, compared to coastal populations with an average body length of about 325 cm (Costa et al., 2016). All bottlenose dolphins have a “melon”, the rounded structure within their forehead, for echolocation (Morrissey, Sumich, and Pinkard-Meier, 2018). They are homeothermic and endothermic (Mann et al., 2000). Tursiops species have an average of 98 teeth total (Jedensjoe, Kemper, and Kruetzen, 2017). Tursiops truncatus have a pale-grey mark that cuts through a darker grey dorsal area towards the bottom of the dorsal fin. Tursiops aduncus exhibit dark spots on the posterior ventral half of the body (Borsa, Andrefouet, and Jencker, 2012). (Borsa, et al., 2012; Costa, et al., 2016; Jedensjoe, et al., 2017; Mallette, et al., 2016; Mann, et al., 2000; Morrissey, et al., 2018)

  • Sexual Dimorphism
  • male larger

Reproduction

Bottlenose dolphins lead a polygynous lifestyle. Males will either form alliances with each other to herd and compete for females to reproduce with or engage individually. Males in alliances work together to separate a female in estrus. They then compete with each other and often flank her to prevent other males from mating with her. An individual male will attempt to mate with a female in estrous when she enters his home range (Mann et al., 2000). (Mann, et al., 2000)

Reproduction in bottlenose dolphins is seasonal, occurring from September to January and peaking from October to December. Most calves are weaned by age four, with ranges from 2.7 to 8.0 years depending on the mother’s gestational status. Most calves are weaned half way through the mother’s next pregnancy. The average time between births for a female is about 4 years. Females exhibit polyestrous cycling and spontaneous ovulation, with a 12-month gestation period. They become sexually mature between 7 and 12 years of age (Mann et al., 2000). Males reach sexual maturity between about 12 and 15 years (Kemper, Trentin, and Tomo, 2014). (Kemper, et al., 2014; Mann, et al., 2000)

Females bear the responsibility and costs of lactation and calf care and protection. Lactation lasts for a period of at least 18-months but can last up to almost twice that. Females must protect their young from predators. Most are gregarious, forming groups with other females in order to protect all of their young (Mann et al., 2000). In the first few days following birth, offspring learn to swim alongside their mother, often by flanking or staying against the mother. The mother must assist the young with this (McBride and Kritzler, 1951). (Mann, et al., 2000; McBride and Kritzler, 1951)

  • Parental Investment
  • precocial
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female
  • post-independence association with parents

Lifespan/Longevity

Female bottlenose dolphins live into their early 50s, while males live 40-45 years (Wells and Scott, 1999). The maximum age recorded in the wild was a 58-year-old female (Kemper, Trentin, and Tomo, 2014). Bottlenose dolphins face mortality due to human-induced impacts such as habitat destruction, getting caught in shark or fish nets, and overfishing of prey species (Peddemors, 1999). (Kemper, et al., 2014; Peddemors, 1999; Wells and Scott, 1999)

Behavior

Bottlenose dolphins are social animals and are active both during the day and at night. They typically live in groups of 2 to 15 individuals, though groups of up to 1000 or even 10000 have been reported. There are three types of groups that typically form including adult females and their offspring, adolescent groups including both females and males, and solitary or pair-bonded adult males. The pair bonds of males may last for 20+ years. Females in a group tend to be related or share long histories. Both wild and captive bottlenose dolphins establish dominance hierarchies in both sexes. Large adult males dominate all others, while the largest females dominate smaller males and females. These hierarchies are maintained through aggressive behaviors that include contact and posturing (Wells and Scott, 1999). They spend their time feeding, traveling, socializing, and idling. Some populations are migratory, while others reside in one area, still others are nomadic (Wilson, Thompson, and Hammond, 1997). They spend most of their time underwater/diving, with about a quarter of the time spent at the surface (Shorter et al., 2017). (Shorter, et al., 2017; Wells and Scott, 1999)

Communication and Perception

Bottlenose dolphins produce three types of sounds including whistles, echolocation clicks, and burst-pulse sounds (also called click-trains). Whistles are used to communicate identity, location, and/or emotional state. Each individual has a signature whistle, which develops in neonates and is stable for life. Male calves have whistles that are similar to their mothers’ whistle, however female calves do not. They may mimic the whistle of others as a precursor to social interaction. Tursiops species have the ability to vocally label objects (Wells and Scott, 1999). Pulses, or clicks, are predominately used for echolocation. However, some burst pulse sounds are used for communication. The peak frequencies for echolocation are about 40-130 kHz (Wells and Scott, 1999). Each click lasts only about a fraction of a millisecond and is repeated as often as 600 times each second. The energy from the sound is reflected back to the source allowing the dolphin to evaluate its surroundings. The phonic lips, enlarged folds of tissue associated with the nasal sacs, are the structures that produce the clicks and whistles. The sounds are then focused by the fatty, rounded forehead structure called the melon to create directional beams of sound. Echolocation is used to perceive surroundings and find prey (Morrissey, Sumich, and Pinkard-Meier, 2018). (Morrissey, et al., 2018; Wells and Scott, 1999)

  • Other Communication Modes
  • mimicry

Food Habits

Bottlenose dolphins have a wide variety of feeding habits. They eat a large variety of fish and/or squid. They prefer drums or croaker fish (Sciaenidae), mackerels and tuna (Scombridae), and mullets (Mugilidae). The diet of bottlenose dolphins varies with local prey availability. Along the central US Atlantic coast both fish and invertebrates are consumed. The four most common fish for that area include Cynoscion regalis, Micropogonias undulatus, Leiostomus xanthurus, and Bairdiella chrysoura. Along the southeastern US coast, fish and cephalopods are consumed. The most consumed species in this area include B. chrysoura, M. undulatus, Cynoscion arenarius, Mugil species, L. xanthurus, and squid species Lolliguncula brevis. Bottlenose dolphins off the coast of South Africa eat fish and cephalopods including Trachurus delagoae, Pomadasys olivaceus, Pagellus bellotti, Scomber japonicus, and cephalopod species Sepia officinalis and Loligo. In the eastern tropical Pacific, inshore Tursiops species tend to feed on fish and invertebrates, while offshore Tursiops species feed on epipelagic fish and cephalopods. Off the coast of Peru, they feed on sardines (Clupeidae), anchoveta (Engraulidae), and hake (Merlucciidae), as well as fish and squids (Wells and Scott, 1999; Barros and Wells, 1998).

Bottlenose dolphins feed in many ways. They feed both individually and cooperatively. They hunt cooperatively by herding schools of prey fish. Individual feeding can involve chasing prey to the surface before capture, hitting a fish with the tail flukes, pushing prey on to the shore, or distracting fish with the tail or by leaping. They also take advantage of human activities to capture prey by driving the fish towards fishermen or feeding behind shrimp trawls collecting discarded fish or stealing fish from fishing gear (Wells and Scott, 1999). (Barros and Wells, 1998; Wells and Scott, 1999)

Predation

The main predators of bottlenose dolphins are large sharks including bull sharks (Carcharhinus leucas), tiger sharks (Galeocerdo cuvier), great white sharks (Carcharodon carcharias), and dusky sharks (Carcharhinus obscurus). It is common to observe shark bites on dolphins that survive these attacks and to find dolphin remains in shark stomachs. Orcas also occasionally prey on Tursiops species. Bottlenose dolphins defend themselves against attacks by butting the predator with their rostra or by striking the predator with their tail flukes (Wells and Scott, 1991). (Wells and Scott, 1999)

  • Known Predators
    • Large Sharks
    • Orcas

Ecosystem Roles

Bottlenose dolphins feed on small fish and squid. They are also hosts to a variety of parasites including flukes such as Braunina cardiformis, tapeworms (Diphyllobothrium species), roundworms (Annisakis species), and thorny-headed worms, (Corynosoma cetacuem) (Wells and Scott, 1999). (Wells and Scott, 1999)

Commensal/Parasitic Species
  • Trematoda (Flukes)
  • Cestoda (Tapeworms)
  • Nematoda (Roundworms)
  • Acanthocephala (Thorny-headed worms)

Economic Importance for Humans: Positive

Tursiops species play an important role in tourism and research for humans. The first bottlenose dolphins were publicly displayed in 1883 (Wells and Scott, 1991). As with other marine mammals, there is tremendous public support, reflected in the growing whale watching industry and visitors to aquariums and zoos. Marine park and zoo animals educate visitors about marine mammals and provide rehabilitation and research (Alex Shorter et al., 2017). (Shorter, et al., 2017; Wells and Scott, 1999)

  • Positive Impacts
  • ecotourism
  • research and education

Economic Importance for Humans: Negative

There are no known adverse effects of Tursiops species on humans.

Conservation Status

Bottlenose dolphins are protected in the United States under the Marine Mammal Protection Act (MMPA). This prohibits any taking of marine mammals from the US waters or by any US citizens in general. It also prohibits the importation of marine mammals and marine mammal products into the United States (NOAA, 2015). Human activities are of concern for bottlenose dolphin conservation as extremely high concentrations of chlorinated hydrocarbon residues have been found in tissues of Tursiops species. Concentrations of polychlorinated biphenyls and dieldrin have also been measured in the blubber of Tursiops species. Calves inherit the majority of their mother’s contaminants leading to increase mortality. These contaminants can also lead to impaired testosterone production in males and reproductive infertility. Human activities such as fisheries, vessel traffic, offshore industrial activity, etc. cause these contaminants (Wells and Scott, 1999). g.Tursiops aduncus is listed in the IUCN Red Data Book as “data deficient,” meaning that there is not enough information known about population numbers, while Tursiops truncatus is currently listed as “least concern” (Hammond et al., 2012). (Hammond, et al., 2012; NOAA, 2015; Wells and Scott, 1999)

  • IUCN Red List [Link]
    Not Evaluated

Other Comments

Bottlenose dolphins have been described in literature dating as far back as ancient Greece and Rome. Tursiops means dolphin-like from the Latin for dolphin, Tursio, and -ops, which is the Greek suffix for appearance (Wells and Scott, 1999). Fossils of Tursiops species have been found from about 5 million years ago (Barnes, 1990). Tursiops species are a descendant of terrestrial mammals from the family Pakicetidae, early Eocene terrestrial whales(Berta, Kovacs, and Sumich, 2015). (Barnes, 1990; Berta, et al., 2015; Wells and Scott, 1999)

Contributors

Nikki Groce (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

female parental care

parental care is carried out by females

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).

migratory

makes seasonal movements between breeding and wintering grounds

mimicry

imitates a communication signal or appearance of another kind of organism

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

nomadic

generally wanders from place to place, usually within a well-defined range.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

polygynous

having more than one female as a mate at one time

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

young precocial

young are relatively well-developed when born

References

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