LENGTH & WEIGHT:Adults males up to 3.2m and 284kg.
SWIMMING ABILITY: Moderately acrobatic slow swimmers (4.8kph).
GROUP SIZE: 1 – 25.
DIET: Variety of fish, molluscs and crustaceans.
BREEDING HABITS: All year round, with most calves born between December & February.
GESTATION: 10 – 12 months.
CALF SIZE: 1m length, weight 25kg.
The Indo-Pacific Humpback dolphin gets its name from the elongated dorsal fin and humped back appearance which arises from the accumulation of fatty tissue on their backs as they age. Some of them may not have the hump, or it may not be as prominent. Another way in which they differ from other dolphin species is in relation to their mounded forehead and long beaks.
Male and female Indo-Pacific Humpback Dolphins grow to a length of between 2.6m and 2.7m reaching physical maturity at around 14 years of age (sexual maturity occurs between the ages of 10 to 13 years). In the wild, these dolphins will live to around 40 years of age.
Indo-Pacific Humpback dolphins can weigh up to 260kg but more commonly weigh around 200kg. Skin colours will vary depending on location and age, with calves being born grey and lightening with age (particularly the dorsal fin and forehead).
In the western Indian Ocean and off the coast of China calves are born with dark colouring that lightens with age to a pink-tinted white colour. Indo-Pacific hump-backed dolphins near Malaysia and northern Australia, however, are nearly white.
Indo-Pacific Humpback dolphins are more leisurely swimmers than some other dolphin species and do not as a rule surf bow waves. They swim in small pods of around five or so dolphins. Each pod is led by an alpha male, or, on occasion, an alpha female. Males will have raking marks on their bodies from fights with other males over territory, and/or female members of its pod.
DISTRIBUTION & HABITAT
Indo-Pacific Humpback dolphins are distributed from the coast of Africa, the Arabian Sea, Indian waters and beyond to the South China Sea. In Australia they inhabit the tropical waters of the west and east coasts and are classified as rare by the EPA (Environmental Protection Agency)and ‘near threatened, population decreasing’ by the IUCN (International Union for Conservation of Nature) Red List of Threatened Species.
Indo-Pacific Humpback dolphins prefer coastal and estuarine habitats in tropical and sub-tropical regions where waters are less than 20m deep. Indo-Pacific humpback dolphins occur in groups of up to 25. In Moreton Bay their reported average group size is 24.
They appear to be subordinate to bottlenose dolphins when feeding near trawlers. They have not been recorded as migrating, although at the northern and southern limits of their range they may move closer to the tropics in the colder winter months.
They live on a diet of fish, prawns, molluscs, crabs, squid and octopus according to the location and season.
What is known about the reproductive biology of Indo-Pacific humpback dolphins has been determined from the South African population. Sexual maturity is attained at 10-13 years, and calving peaks in spring and summer.
A three-year calving interval has been suggested, and gestation lasts 10 to 12 months. Weaning age is not known with certainty but females may lactate (produce milk) for more than two years. Strong mother and calve associations last for at least 3 to 4 years.
Living close to coasts and rivers, the Indo-Pacific Humpback dolphin is especially susceptible to pollution as well as shark and fishing nets. Other threats include overfishing of their habitat, noise pollution affecting their sonar location, marine activities, harassment and coastal development.
They have nowhere to go when their environment is damaged. Indo Pacific Humpback dolphins are shy dolphins so it is a rare privilege to interact with this species so closely.