INDO-PACIFIC BOTTLENOSE DOLPHINS

(Tursiops aduncus)

Bottlenose Dolphin

Bottlenose Dolphin (Tursiops aduncus) (c) E. Hawkins

Physical Features

  • Length: Adult: to around 2.7m; Newborn: 85cm-112Cm
  • Weight: Adult: to around 230kg; Newborn: 15-30kg
  • Colouration: Bottlenose Dolphins are dark gray on the upper dorsal side, along the tail stock, tail flukes, rostrum and pectoral fins.  The underbelly is pale gray to white. Mature animals have ventral speckling.  May also have pale blaze on sides. Colouration may change between regions with some appearing darker than other.
  • The Bottlenose Dolphin is one of the most abundant species that occurs along the coastal regions of the temperate and tropical areas of the world.
  • The size and colour of bottlenose dolphins varies between geographic regions.  Generally, larger, darker forms are found in the cooler regions and smaller, lighter forms are found in the warmer regions.
  • Bottlenose Dolphins have 21-29 teeth along the upper jaw and 36-48 teeth on the lower jaw.
  • The dorsal fin of a Bottlenose Dolphin has a pointed tip and curved trailing edge.
  • The dorsal fins of Bottlenose Dolphins are used to identify individuals.  Each dorsal fin has a unique shape, arrangement of notches and scars.
  • There are generally two ecotypes found in most regions, the coastal or inshore form and the offshore form.
  • It is difficult to determine males and females in the wild.  Generally sighting of the genital slits on the under-belly near the tail flukes is required to confirm the sex of a dolphin (Figure below).
Dolphin genital slits

Figure shows underbelly of dolphins indicating sex differences

Biology & Ecology

  • Bottlenose Dolphins can hold their breath for up to 15 minutes.
  • Dolphins are carnivorous and feed on a variety of sea life including fish and squid.
  • A layer of fatty tissue under the skin, called blubber, maintains the dolphin’s body heat.  This layer of fat also provides an important energy source.
  • Dolphins have very good eyesight both above and below the water.
  • Following a gestation period of 12months, dolphins give birth to live young.
  • A bottlenose dolphin calf will drink milk for at least 6 months and remain with its mother for up to 4 years.
  • Age of maturity varies between genders, with female bottlenose dolphins reaching maturity between 8-10 years and males between 10-12 years of age.
  • Bottlenose Dolphins can live for over 50 years.

Behaviour & Social Organisation

  • Bottlenose Dolphins are very social animals and live in complex societies that can often be sexually segregated and have a dominance hierarchy.
  • Groups of Bottlenose Dolphins usually range between 1-10 individuals in size.
  • Mature males may form a strongly bonded alliance with at least four other males.
  • Females live in large groups and maintain a large network of associates within their home range.
  • Dolphins display many different types of behaviours including leaping, surfing, bow riding, and tail-slapping.
  • Byron Bay and its surrounding waters are an important habitat for over 800 ‘resident’ and ‘transient’ Bottlenose Dolphins.

Acoustic Communication

  • Dolphins produce a diverse range of sounds that include echolocation or sonar clicks, whistles, burst pulse sounds such as ‘squawks’ and ‘squeaks’.
  • ‘Whistles’ are thought to be used to maintain contact, identify, and to locate other dolphins.
  • ‘Clicks’ are used for echolocation, assisting in navigation and feeding.
  • Burst-pulse sounds not only assist in foraging and deciphering details about targets such as fish and other prey, but also have communicative functions.  Little is known about the use of this diverse group of sound types produced by Bottlenose Dolphins.