Bottlenose Dolphin
Bottlenose dolphin (Tursiops truncatus)
Common bottlenose dolphin (Tursiops truncatus). 
Next Species -----> <----- Previous Species
Classification:
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Delphinidae
Genus: Tursiops
Species: Tursiops truncatus
Montagu, 1821
Get the Facts:
Bottlenose dolphins are the most well studied cetacean species around the world and the most recognised species due to their cosmopolitan distribution, appearance in films such as "Flipper" and the fact that they are commonly captured for the aquarium trade. Bottlenose dolphins are highly intelligent and have been shown to have self recognition, use mimicry, language, object classification and tool use. An example of tool use in bottlenose dolphins is "sponging" - i.e using marine sponges to cover their rostrum (beak) to protect it while foraging for food sources on the seabed. They also show culture - passing language down from generation to generation, just like humans! Their high intelligence has led to interactions with humans that are mutually beneficial, for example in some areas they co-operate with local fisherman by driving fish into their nets and they eat the fish that escape. 

Species Identification:

Common bottlenose dolphins can weigh 300 kg on average and reach lengths of over 4 meters. Their colour can vary from dark grey on the back to lighter grey on the flanks, and also blueish-grey, brownish grey or even nearly black. They are often darker on the back from the rostrum to behind the dorsal fin and exhibit countershading - a form of camouflage where they are paler on their ventral side or bellies. Bottlenose dolphins have a tall curved dorsal fin that is slightly hooked with a broad base.  They have a thick tail stock and their tail flukes are small in relation to their overall body size. Like other odontocetes or toothed whales, they have a single blow hole. They have a pronounced "bottle-shaped" beak and a shark crease between the beak and the melon. They are very acrobatic and can often be seen from a distance breaching and making big splashes of white water. Other common behaviours observed include bow riding, tail slaps, peduncle dives and surface rushing in pursuit of prey.

Diet:

Bottlenose dolphin have a varied diet depending where in the world they are located. In Ireland, bottlenose dolphins are generalist predators and feed on fish species, cephalopods and crustaceans, with individual animals specialising on particular prey species.. Recent studies carried out on the stomach contents of bottlenose dolphins stranded in Ireland by Dr. Gema Hernandez-Milian and Professor Emer Rogan indicated that  27 different prey species of both fish (79.1%) and cephalopods (20.9%). Fish species found to be part of their diet included gadoids (mainly pollock, saithe and haddock), horse mackerel, conger eel, flatfish and dogfish. Until recently dogfish had not been found in the diet of bottlenose dolphins, although one study did find a dogfish in the oesophagus of a bottlenose dolphin, causing the animal to choke to death. In Ireland, significant differences have been found between male and female bottlenose dolphin diet, and between populations - particularly in dolphins that were found stranded live and stranded dead, suggesting the latter fed in pelagic open water. 

Habitat:

Three distinct populations of bottlenose dolphins have been identified in Irish waters using genetic markers and photo-identification, which show these populations have differences in diet which suggests they forage in different habitats. The three distinct populations recognised in Irish waters include an offshore group, a coastal transient group and a small population of resident bottlenose dolphins of 140 - 170 individuals in the Shannon Estuary, Co. Clare. A semi-resident group of six to ten bottlenose dolphins have also been described in Cork Harbour, along with a group likely of the coastal transient inshore population that occasionally use Cork Harbour as a foraging ground. Read more about ORCA's Bottlenose Dolphin Project. 

Bottle-nosed Dolphin (Tursiops truncatus)
Behaviour:
Bottlenose dolphins have a varied repertoire of surface and vocal behaviours. In 2014 - 2016, Dr. Isabel Baker developed the first ethogram of bottlenose dolphin behaviour in Ireland, which consisted of 11 activity states and 45 different behavioural events. The most commonly recorded activity state was travel (52%), while the most commonly recorded behavioural event was slow travel (40%), surface rush (28%) and leap (28%). Other behaviours less commonly observed included peduncle dives, tail out, tail slap, head out, chin slap, pectoral slap, pectoral rub and more. Aggressive behaviour observed in bottlenose dolphins include biting, ramming and tail slaps. Bonding and acceptance behaviour include stroking and rubbing. Often people wonder how these marine mammals who must surface to breathe, sleep. Dolphins can essentially "turn off" half of their brain, allowing them to rest but also carry out survival dependant behaviours such as surfacing to take a breath. Bottlenose dolphins also engage in epimeletic behaviour, i.e. they assist injured or impaired individuals within their group, such as holding an injured dolphin at the surface of the water to breathe. Epipeletic behaviour is most commonly observed among mothers and calves who have died. 
Social Structure: 
Bottlenose dolphins are very social animals and have a complex "fission-fusion"  social structure with sex specific patterns of associations and aggressions, most prominent during non-feeding behavioural states due to mating strategies and more relaxed during feeding events. Fission fusion social structure involves subgroups that frequently join or leave the main group. They are very active animals and can swim at speeds of 3 and 6km/hr. Bottlenose dolphins can form various kinds of groups, including nursery groups (mothers and calves), juvenile groups (young dolphins of both genders up to their mid teens), adult male groups (individually separated or as strongly bonded pairs).  Studies on the Shannon Estuary bottlenose dolphins have found non-random associations between individuals which can persist greater than 1,000 days. Bottlenose dolphins in the Shannon Estuary have also been shown to change their group composition and associations regularly. 
Vocalisations:
Bottlenose dolphins exchange information with group members using a wide variety of vocalisation types, such as whistles, squawks, chips, pops, yelps, moans, and burst pulse calls associated with specific behaviours. In addition they also communicate with tactile i.e. touch behaviours. Bottlenose dolphins also use high frequency echolocation clicks (110 - 130 kHz) and buzzes to find prey, similar to bats. Open mouth vocalisations such as whistle-squawks and burst pulse sounds have been shown to be associated with aggressive behaviours as well as sexual play. Click trains are produced as an individual explores an area and during social interactions. Whistles are produced in group-settings during instances of aggression, in association with play behaviours, conspecific rubbing, during mother-calf reunions and for individual recognition. Each bottlenose dolphin has its own signature whistle akin to a name that they use to identify each other. Whistles serve as a communicative function and have been well documented among socialising bottlenose dolphins. 
Reproduction:
Female bottlenose dolphins become sexually mature between 5-10 years old and males between 8-13 years. Reproductive seasons vary from region to region, with females ovulating at certain times of the year, while males are sexually active through-out the year. Bottlenose dolphins are polygamous. They engage in mating behaviour either in alliances or individually. Males that form alliances search for females that are in estrous and then separate her from the group to mate with her. They may flank a female to prevent competitive males in the alliance to mate with her and it can take weeks for a female to become receptive to mating. Bottlenose dolphin copulation typically occurs belly to belly. Gestation lasts for a period of 12 months and females give birth to a single calf. Female bottlenose dolphins reproduce every 3- 6 years. They nurse their young from nipples on each side of their genital slit until the calf is 18-20 months old. Females give birth at any time of the year but it is more frequent during summer months. Female bottlenose dolphins can reproduce into their late forties and then go through menopause, similar to humans. 
Lifepsan:
Bottlenose dolphins are threatened by a variety of factors both natural and human induced. The former includes disease and predation and the latter includes injury. Males typically live about 40 to 45 years and females over 50 years. The oldest female documented was 53 years old. 
Bottlenose dolphins of the World:
Molecular studies have revealed the genus contains three species; the common bottlenose dolphin (Tursiops truncatus), the Indo-Pacific bottlenose dolphin (Tursiops aduncus), and the Burrunan dolphin (Tursiops australis). 
Population Status:
The worldwide population population of common bottlenose dolphin is about 600,000 animals. Indo-Pacific bottlenose dolphins are abundant, but the overall population is unknown. Burrunan dolphins have two geographically  distinct resident populations; one in Port Philips, with a population of 100 individuals and the other in Gippsland Lakes, with a population of 50 individuals. The  Burrunan dolphins are listed as Endangered under the Victorian Flora and Fauna Guarantee Act and as Data Deficient according to the IUCN Red List. 
Global Distribution:
Common bottlenose dolphins occur in almost all tropical and temperate regions and can be found in both coastal and offshore waters. Worldwide bottlenose dolphins can be found in the Mediterranean and Black Seas, in addition to the south-western Indian Ocean. In the Atlantic Ocean, to the west they can range from as far north as Georges Bank (off Massachusetts ) and in the east, in Irish waters and the British Isles to Argentina and northern Nambia. In the Pacific Ocean they range from west coast of California, Organ and Washington, and in the Hawaiian Islands. They are also found in the coastal waters along the East coast from New York to Florida, through-out the Gulf of Mexico and in the Caribbean. 
Conservation Threats:
Bottlenose dolphins are exposed to a variety of threats due to their coastal tendencies which expose them to human activities. Some of the more pressing threats include interactions with fishing gear, habitat destruction and degradation, biotoxins, and illegal harassment. Dolphins can become entangled or incidentally captured in commercial fishing gear such as gillnets, seine nets, trawls, trap pots and longlines. Dolphins may also encounter rod and reel gear used by recreational anglers as a result of them taking the bait and the catch directly from fishing gear (i.e. depredation). They can also face threats from food provisioning by eco-tour operators to encourage them to stay in an area. Dolphins inhabiting areas close to shore are susceptible to habitat degradation by contaminants from industry and oil spills. For example, dolphins living in areas with high levels of PCB's  as those affected by the 2010 Deepwater Horizon oil spill were shown to have impaired immune systems and reductions in their reproductive out-put.  As well as threats from contaminants, physical habitat degradation from shoreline developments, offshore wind-farm developments and increased boat traffic is also of concern.
Share by: