The below information is sourced from: Review of the Conservation Status of Australia’s Smaller Whales and Dolphins - Graham J. B. Ross - February 2006

Indo-pacific Humpback Dolphin (Sousa chinensis)

The level of information available on the biology and habitat of Sousa chinensis, in relation to threats or potential threats it faces, is too limited to support reassessment of its currently assigned status. It is therefore recommended that its status remain as K.

To determine the conservation status of Sousa in the Australian region, and meet the objectives of The Action Plan for Australian Cetaceans, it will be necessary to survey and estimate population size across the entire range of this species in Australian waters, from 34ºS on the east coast to 25ºS on the west coast. This survey would aim to determine the number of animals and their relationship with other Sousa, using photo-identification and acoustic techniques, to establish an estimate for the Australian population. The survey would benefit by incorporating biological material from all deceased animals, and biopsy samples from as many live Sousa as possible, to determine through genetic and other studies: the species status, the sex of individuals, their levels of hormones and pesticides; relationships, and degree of philopatry in Australian Sousa.

Family: Delphinidae. Indo-Pacific Humpbacked Dolphin, Sousa chinensis (Osbeck, 1765)

EPBC Act Status: Cetacean; Approved Recovery Plan: none

Conservation Status: The Action Plan for Australian Cetaceans status – insufficiently
known (K) IUCN status: Insufficiently known/Data Deficient

CITES Status: Appendix I

Bonn Convention: migratory species

Sousa chinensis: Census of Australian Vertebrate Species 1655, updated 31 Dec. 1998.

Taxonomic status. Described by Osbeck in 1765, from the coast of China. The holotype has been destroyed; a neotype for Sousa chinensis has been selected and described by L.J. Porter (2002). The genus comprises five nominal species - S. teuszi in West African waters, and four Indo-Pacific species: S. plumbea, S. lentiginosa; S. borneensis, and S. chinensis. While recent morphological studies suggest that there may be as few as one species only, with two subspecies, to the east and west of the Bay of Bengal (Ross et al. 1995), the results of recent genetic studies by Cockcroft and Smith-Goodwin (2002) contradict a number of conclusions drawn on morphological grounds. Complementary studies on genetic material from much of the range of the genus will provide an invaluable comparison with the results of the morphological studies.

Distribution. Based on the premise of a single species in the genus, Indo-Pacific Humpbacked Dolphins are distributed more or less continuously as local residents along the coast from False Bay, South Africa to the South China Sea, including the Red Sea, Arabian Gulf, the Indian subcontinent, Gulf of Thailand, Malacca Straits and northern Borneo, and the coast of China to the Changjiang River (31° 50'N). At least one animal reached the Mediterranean via the Suez Canal, the first known case of anthropogenic range extension for a marine mammal through habitat modification (Kerem et al. 2001). The distribution of Australian Sousa extends to 25°S on the west coast, and 34°S on the east coast, aided by from the warm eastern boundary current; similarly those resident in southern South Africa live at 34°S in water temperatures of 15-22°C (Bannister et al. 39 1996). There is evidence of seasonal changes in abundance, as indicated by sighting rates in some populations, for example, in southern Africa, India and China (Parsons 2002).

Conservation objectives.

The six conservation objectives are:

• To determine distribution and to monitor abundance, especially in key areas; The distribution of Indo-Pacific Humpbacked Dolphins in Australian waters is understood in broad terms, based largely on the relatively few records of strandings and captures. There are no data on absolute abundance. Fifty individuals have been photo-identified in Moreton Bay; estimates for Moreton Bay in 1984-1986, and 1985-1987 respectively were: 163 animals (95% confidence intervals 108-251), and 119 animals (95% confidence intervals 81-166); preliminary results for Cleveland Bay, in the Central Section of the Great Barrier Reef, suggest a population less than 200 animals (Parra et al. 2002). Data from Dugong aerial surveys along the Queensland coast provide minimum estimates of Indo- Pacific Humpbacked Dolphins. These counts are uncorrected for submerged animals. Surveys to determine the abundance of this species between 25°S on the west coast, and 34°S on the east coast, using acoustic techniques, verified against localised photo-identified groups, should provide an estimate of abundance on which the conservation status of this species can be assessed.
  
• To determine possible impact of threats, such as pollutants, incidental capture and habitat degradation: Levels of pollutants should be determined from all available carcases, together with analysis of skin and blubber biopsies, preferably sampled across the distribution of this species in Australia. Prey species in deceased dolphins could be identified from fish otoliths recovered from stomach contents, and determined against reference collections. To study habitat requirements to assess impacts of degradation; Studies on habitat degradation in relation to assess possible impacts on Indo-Pacific Humpbacked Dolphins have not been pursued as yet.
  

In Australian waters, Indo-Pacific Humpbacked Dolphins attain lengths of 262 cm in males and 260 cm in females. Age and lengths of South African animals at physical maturity is 13-14 years, and 2.58-2.74 m; maximum weight recorded is 260 kg (male) and 170 kg 40 (female); maximum age is more than 40 years and maximum length 2.74 m (Ross et al. 1994; Bannister et al. 1996). Reproductive data derived from Australian and South African dolphins: length and weight at birth 0.97-1.08 m and ca 14 kg; age and length at weaning not known; age at sexual maturity 10-13 years; mating season, gestation period, and calving interval unknown; calves born in summer; no calving areas known in Australian waters (Bannister et al. 1996). Goodwin (1997) indicated that Indo-Pacific Humpbacked Dolphins show strict female philopatry; Atkins and Atkins (2002) were less certain about the state of philopatry in Richards Bay, Natal, but stated that a small proportion of the animals could be considered resident.

Biology. These dolphins inhabit coastal, estuarine, and occasionally riverine species, in tropical and subtropical regions. The species occurs close to the coast, generally in less than 20 m depth. Aerial surveys in the Great Barrier Reef region have located Sousa in waters between the outer reef and the mainland, further offshore than has been reported in the literature (Corkeron et al. 1997; Marsh 1990). Key localities include Moreton Bay, Queensland and the lower reaches of the Brisbane River and adjacent offshore waters, where a resident population occurs in water less than 10 m in depth, and offshore to 6 km. Tin Can Inlet, Great Sandy Strait, Queensland, features a group which, until recently, approached humans for food. Several groups appear to be resident within Ningaloo Reef, north-western Australia (Bannister et al. 1996).

Indo-Pacific Sousa are not known to be migratory (Ross 2002), although numbers of animals increase seasonally in South Africa. Some seasonal inshore-offshore and longshore movements are recorded for West African Sousa (Bannister et al. 1996). Teleost fishes, some cephalopods and crustaceans, as well as littoral, estuarine and demersal reef species are eaten. Indo-Pacific Humpbacked Dolphins feed in association with prawn trawlers in Moreton Bay, and presumably elsewhere throughout the species’ range in Australia (G. Ross et al. 1994; Bannister et al. 1996).

Threat Summary. Past and current threats include: presumed habitat destruction and degradation, including noise pollution, harassment, particularly close to major cities (e.g. in Moreton Bay) (Bannister et al. 1996); incidental capture through drowning in inshore gillnets set across rivers, and estuaries to catch barramundi and other fish species. Shark nets set for the protection of swimmers, killed 18 Sousa in 1968-2001, 11 of which were from nets at Townsville and Cairns (Parra et al. 2002) – despite the low numbers killed per year in such shark nets, they may have a significant impact on social structure of cetaceans such as Sousa, given their philopatric nature and small group size; trawl-nets, drift-nets; illegal killing, particularly by people killing for sport, e.g. spearing or shooting (there is no evidence of direct killing of Sousa in Australian waters - Parra et al. 2002); live capture in Qld (permits granted for up to 12 per year at present) and northern NSW; overfishing of prey species. Potential threats: pollution, particularly from organochlorines, because inshore cetaceans are very vulnerable, especially in agricultural regions; epizootics, marine mammals being very susceptible to pathogen-induced mass mortalities (Bannister et al. 1996). Interaction with tourism operators of dolphin-watching and dolphin-feeding activities is increasing, e.g., at Tin Can Bay, south-eastern Queensland, and on boats, with the potential for adverse reactions by the dolphins. Frequencies of whistles produced by Australian Indo-Pacific Humpbacked Dolphins (1.2-16 kHz; Schultz and Corkeron 1994) and broad band clicks (2-22 kHz; van Parijs and Corkeron, 2001) coincide with frequencies emanating often from boat traffic, suggesting that noise pollution may a problem for this species. Determination of the level of philopatry in this species and others that live in small groups is important, as the impact of the loss of reproductive females from such groups is potentially greater than that for species forming large schools.