Bottlenose dolphin - Tursiops truncatus and T. aduncus

Bottlenose dolphins are probably the best-known species of dolphin– the species upon which everyone’s classical image of ‘a dolphin’ is based.

The iconic ‘Flipper’, star of television programmes and films since the 1960’s, was a bottlenose dolphin, as are the majority of captive dolphins performing in marine parks around the world.

Bottlenose dolphins are found in almost every ocean and sea, other than the coldest waters toward the poles. At present there are two recognized species of bottlenose dolphin, and in some cases, both species can be found in the same area.

These are the **common bottlenose dolphin** (*Tursiops truncatus*), and the **Indo-Pacific bottlenose dolphin** (*Tursiops aduncus*).

In addition to this species distinction (see more details below), there is a great deal of variation between inshore and offshore populations of common bottlenose dolphins in different parts of the world.

Populations differ greatly in average length, weight, appendages, external colouration, diet and behaviour.

A third possible species -the Burrunan dolphin -has been proposed for inshore populations of bottlenose dolphins in Australia1, and scientists and geneticists around the world have dedicated a great deal of effort to better understanding the taxonomy of bottlenose dolphins.

Like humans, different populations inhabit a wide variety of environments, and have adapted special diets, behaviour patterns, and external features to adapt to those habitats2.

Wherever they are found, however, bottlenose dolphins tend to be one of the more approachable and active dolphin species, making them a popular target for dolphin watching activities.

## Distribution:

Common bottlenose dolphins occur in all almost all tropical and temperate regions, and can be found in both coastal and offshore waters3. They are found in most enclosed or semi-enclosed seas (e.g. North Sea, Mediterranean, Black Sea, Persian Gulf), and frequent bays, lagoons, channels and river mouths4.  Indo-Pacific bottlenose dolphins have a more restricted range with boundaries at the southern tip of Africa to the west, and the Solomon islands/New Caledonia to the east. They are generally limited to coastal and inshore waters on the continental shelf, although they are also found around some Indo-Pacific island groups4.

Common Bottlenose dolphins are native to the following countries\*\*: Albania; Algeria; American Samoa; Angola; Anguilla; Antigua and Barbuda; Argentina; Aruba; Australia; Bahamas; Bahrain; Bangladesh; Barbados; Belgium; Belize; Benin; Bermuda; Bonaire, Sint Eustatius and Saba (Saba, Sint Eustatius); Bosnia and Herzegovina; Brazil; Brunei Darussalam; Bulgaria; Cambodia; Cameroon; Canada; Cape Verde; Cayman Islands; Chile; China; Cocos (Keeling) Islands; Colombia; Comoros; Cook Islands; Costa Rica; Côte d'Ivoire; Croatia; Cuba; Curaçao; Cyprus; Denmark; Djibouti; Dominica; Dominican Republic; Ecuador; Egypt; El Salvador; Falkland Islands (Malvinas); Faroe Islands; Fiji; France; French Guiana; French Polynesia; Gabon; Gambia; Georgia; Germany; Ghana; Gibraltar; Greece; Grenada; Guadeloupe; Guam; Guatemala; Guernsey; Guinea; Guinea-Bissau; Guyana; Haiti; Honduras; Hong Kong; India; Indonesia; Iran, Islamic Republic of; Ireland; Isle of Man; Israel; Italy; Jamaica; Japan; Jersey; Kenya; Kiribati; Korea, Republic of; Kuwait; Lebanon; Liberia; Libya; Madagascar; Malaysia; Maldives; Malta; Marshall Islands; Martinique; Mauritania; Mayotte; Mexico; Micronesia, Federated States of ; Monaco; Montenegro; Morocco; Mozambique; Myanmar; Namibia; Nauru; Netherlands; New Caledonia; New Zealand; Nicaragua; Nigeria; Niue; Northern Mariana Islands; Oman; Pakistan; Palau; Panama; Papua New Guinea; Peru; Philippines; Pitcairn; Portugal; Puerto Rico; Qatar; Réunion; Romania; Russian Federation; Saint Helena, Ascension and Tristan da Cunha; Saint Kitts and Nevis; Saint Lucia; Saint Martin (French part); Saint Pierre and Miquelon; Saint Vincent and the Grenadines; Samoa; Sao Tomé and Principe; Saudi Arabia; Senegal; Seychelles; Singapore; Sint Maarten (Dutch part); Slovenia; Solomon Islands; Somalia; South Africa; Spain; Sri Lanka; Suriname; Syrian Arab Republic; Taiwan, Province of China; Tanzania, United Republic of; Thailand; Togo; Tonga; Trinidad and Tobago; Tunisia; Turkey; Turks and Caicos Islands; Ukraine; United Arab Emirates; United Kingdom; Uruguay; Vanuatu; Venezuela, Bolivarian Republic of; Viet Nam; United Kingdom, United Sates.; Wallis and Futuna; Western Sahara; Yemen

Indo-Pacific humpback dolphins are native to: Australia; Bahrain; Bangladesh; Brunei Darussalam; Cambodia; China; Comoros; Egypt; Eritrea; India; Indonesia; Iran, Islamic Republic of; Japan; Kenya; Madagascar; Malaysia; Mayotte; Mozambique; Myanmar; Oman; Pakistan; Papua New Guinea; Philippines; Saudi Arabia; Singapore; Solomon Islands; Somalia; South Africa; Sri Lanka; Taiwan, Province of China; Tanzania, United Republic of; Thailand; Timor-Leste; United Arab Emirates; Yemen

## Biology and Ecology:

### Feeding:

Bottlenose dolphins feed on a wide variety of prey, with different populations favouring various species of fish, squid and sometimes crustaceans depending on the habitat they occupy3,4.  Nearshore populations generally favour bottom-dwelling fish, and noise producing fish like croakers and grunts3,5,6, while other (including offshore) populations eat schooling fish like mullets and other species, including  mackerels, tunas, and bonitos3,7.   Bottlenose dolphins are known to employ a range of feeding techniques, including some highly specialised and creative behaviours, such as the use of sponges to protect their beaks as they dig in the sand for prey8, and cooperative strand feeding, in which a line of dolphins works in unison to force fish toward the shore and then half-beach themselves to grab the flapping fish before sliding back into the water.

### Social Structure, Reproduction and Growth:

Bottlenose dolphins can occur in small groups of 2-15, or as many as 1000 individuals, with inshore populations typically occurring in smaller groups than offshore populations3.  In many bays, sounds, and estuaries where they have been studied, such as Sarasota Bay, Florida, common bottlenose dolphins have been found to year-round residents, remaining in the same area for multiple decades and many generations9. They are highly vocal, and produce three main categories of sounds: whistles, echolocation clicks and burst-pulse sounds.   Bottlenose dolphin vocalizations have been studied both in captive and wild animals, and include a ‘signature whistle’, which is unique to each individual, and seems to be used to communicate identity, location, and possibly even an emotional state10.

Female common bottlenose dolphins reach sexual maturity at an age of 5-13 years, with males following at 9-14 years3.  Calves are born roughly 12.5 months after a female is impregnated, and feed on the mother’s milk for the first year or two of life.  Mothers actively teach their young how to hunt, and calves start to supplement their diet with solid food from 4-6 months onward.  Females look after their young for 3-6 years, typically separating from each other when the next calf is born3.

Males have been shown to have hierarchies and engage in aggressive interactions, but Indo-Pacific males also sometimes cooperate with other males to coerce a female into mating11 and common bottlenose dolphin males often work with a strongly bonded, long-term male alliance member to guard receptive females from approaches by other males12.   Males typically are more heavily scarred than females and may show more damage on their dorsal fins, including characteristic tooth rakes from interactions with other male dolphins13.

## Research, threats and conservation:

Much of what we know about dolphin biology, learning, and social structure has been learned by closely studying the many bottlenose dolphins under human care around the world. These dolphins have been used in experimental settings to understand how their echolocation works, how they communicate with each other, how they ‘sleep’ and how they learn new skills. They have also been used by the military to perform underwater tasks considered too risky for human divers, and are the species most often trained to perform in marine parks around the world.

However, researchers also have increasingly sophisticated techniques to learn about dolphins in the wild.  Photo-identification studies, in which individual dolphins are photographed and recognized over time by the unique nicks and scars on their dorsal fins, allow researchers to monitor individual’s movements and life histories over time.  In well-studied populations, such as bottlenose dolphins in Sarasota Bay, Florida, individual dolphins and their communities have been followed over more than 48  years, allowing researchers to construct family trees and measure life history parameters, reproductive success, and birth and mortality rates9.  Use of hydrophones to record vocalizations, genetic sampling, satellite tagging, and many other techniques yield additional valuable understanding of populations and how to protect them. Read more about these techniques here.

### Natural Predators:

Bottlenose dolphin`s main natural predators are sharks, and photo-identification studies have revealed scarring associated with shark attacks in several populations14-16.  Sting-ray barbs and aggression between dolphins have also been indicated as causes of death in some cases3.

### Human-induced threats:

As with all whales and dolphins, accidental entanglement in fishing gear – or bycatch- is the leading source of human-induced mortality for bottlenose dolphins.  This is particularly true in coastal areas where large-mesh gillnets are the predominant fishing gear used, as these are often set and left unattended for long periods of time, entangling dolphins as they travel or chase fish into the nets17-20.  In some coastal areas, recreational fishing gear is the primary source of mortality and serious injury21.  Agricultural and industrial run-off in areas of dense human habitation are also associated with high contaminant levels in coastal populations of bottlenose dolphins 22-25, and increased contaminant loads have been linked to high death-rates among first-born calves that receive high loads of contaminants in the mother’s milk26.  Bottlenose dolphin deaths have also been linked to blooms of harmful algae, sometimes called ‘red tides’ that can occur naturally, but are sometimes linked to run-off from heavily populated or farmed areas27,28.

### Conservation status:

It is difficult to assign a conservation status to either common or Indo-Pacific bottlenose dolphins on a global or range-wide basis.  Indo-Pacific bottlenose dolphins are particularly difficult to assess, because they tend to occur in fragmented coastal populations, and their range includes many countries where little or no formal research has taken place.  As such, the species is designated as Data Deficient in the IUCN Red List of Threatened Species.  Common bottlenose dolphins are considered Least Concern by the IUCN on a global level, but this may be deceiving, as many populations are undergoing serious declines, including: bottlenose dolphins in the Mediterranean, where the species is considered Vulnerable to extinction; and the Black Sea where previous hunting and live captures and ongoing high rates of fisheries bycatch have led to an IUCN Endangered status and a CMS Appendix 1 listing.  The Fjordland bottlenose dolphin population, which includes Doubtful Sound, New Zealand, is considered Critically Endangered 29,30, and declines may be linked to pressure from dolphin watching31.  In general, resident coastal populations of bottlenose dolphins are most at risk of declines in health or numbers due to the overlap of their habitat with a variety of human activities, including fishing, agriculture, industry, and vessel traffic.

## Bottlenose dolphins and whale watching:

Please see the IWC Whale watching Handbook.

Gallery Of Images For This Article:

Common bottlenose dolphin global distribution. Adapted by Nina Lisowski from Jefferson, T.A., Webber, M.A. and Pitman, R.L. (2015). “Marine Mammals of the World: A Comprehensive Guide to Their Identification,” 2nd ed. Elsevier, San Diego, CA. Copyright Elsevier: http://www.elsevier.comCommon bottlenose dolphin in the Canary Islands. Photo courtesy of Fabian Ritter/MEEReV.Indo-Pacific bottlenose dolphins tend to be smaller and more slender than common bottlenose dolphins (T. truncatus). T. aduncus maximum Adult length is 2.6 m, and maximum weight for an adult male is 230 kg (male). A newborn is 84-112cm /9-20kg Photo courtesy of Chris Parsons.Indo-Pacific bottlenose dolphin distribution. Adapted by Nina Lisowski from Würsig,B., Thewissen, J.G.M. and Kovacs, K.M. Editors (2018) "Encyclopedia of Marine Mammals", 3rd ed. Academic Press, Elsevier: San Diego. CA. Copyright Elsevier: http://www.elsevier.comIndo-pacific bottlenose dolphin in the Red Sea. Photo courtesy of Chris Johnson.Common bottlenose dolphin off the coast of Colombia. Photo courtesy of Santiago Cañón, Fundación Omacha.