Sousa chinensis (Osbeck, 1765)
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https://doi.org/ 10.5281/zenodo.6610922 |
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DOI |
https://doi.org/10.5281/zenodo.6611050 |
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persistent identifier |
https://treatment.plazi.org/id/BD4CCC61-763E-FFF6-FFD3-FB63EE75F262 |
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Diego |
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scientific name |
Sousa chinensis |
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15. View On
Indo-Pacific Humpback Dolphin
French: Dauphin de Chine / German: Indopazifik-Buckeldelfin / Spanish: Delfin jorobado indopacifico
Other common names: Borneo White Dolphin, Chinese White Dolphin, Lead-colored Dolphin, Plumbeous Dolphin, Ridge-backed Dolphin, Speckled Dolphin, White Dolphin; Pacific Humpback Dolphin (chinensis type); Indian Humpback Dolphin (plumbea type)
Taxonomy. Delphinus chinensis Osbeck, 1765 View in CoL ,
Zhujiang Kou (mouth of Canton [Pearl] River, Guangdong Prov., China.
Taxonomy of S. chinensis is currently in dispute. As currently defined, S. chinensis consists of at least two types, plumbea type in the western Indian Ocean from South Africa to the east coast of India, and chinensis , also from the east coast of India, China, and Australia. Morphological evidence for naming these two types includes differing external morphology and skull morphometrics, but these traits could be a result of convergent evolution. Analyses of mtDNA from recent studies show that S. chinensis from Australia are genetically distinct from other populations. Phylogenetic comparisons indicate that Hong Kong S. chinensis , South African plumbea type, and Atlantic S. feuszii are more closely related to each other than to the Australian population of S. chinensis . Presently, only the eastern Taiwan Strait population is recognized as being distinct and isolated. Monotypic.
Distribution. Coastal tropical to subtropical waters of the Indian Ocean and W Pacific, Ocean. View Figure
Descriptive notes. Total length up to 280 cm; weight up to 250-280 kg. Neonates are c.100 cm long. The Indo-Pacific Humpback Dolphin has medium-sized, robust body. Its dorsal fin and associated hump vary distinctly between extremes of their distribution. Dorsal fin in the eastern reaches of its distribution is short and slightly recurved, with wide,laterally sloping hump. In the west, dorsal fin is sharply recurved and smaller, with broad hump. Skin pigmentation also varies throughout its distribution and within developmental stages. Pale-colored young off South Africa darken with age, and adults are dark gray dorsally, with off-white ventral side. Indo-Pacific Humpback Dolphins in this part of their distribution have little to no spotting. Individuals in the east, such as those in the eastern Indian and Pacific oceans, are born with dark-gray pigmentation and become paler with age. Dark young off South-east Asia and Australia also tend to become paler with age but retain dark spotting and blotches. Some adult Indo-Pacific Humpback Dolphins lose all their dark pigmentation and are completely white, with pinkish tinge. In some areas of their distribution, Indo-Pacific Humpback Dolphins display sexual dimorphism. In African waters, males average 226 cm in length, and females are smaller, averaging 216 cm. In other parts of the distribution, such as off Hong Kong, there does not appear to be any significant sexual dimorphism. Rostrum of the Indo-Pacific Humpback Dolphin is long and narrow, with indistinct junction to posterior, moderately sized melon. There are 31-39 teeth in upper jaw and 29-38 in lower jaw. On average, Indo-Pacific Humpback Dolphins in the western part of their distribution have more teeth than those in the eastern part of their distribution.
Habitat. Typically in tropical and warm temperate coastal waters less than 20 m deep, associated with estuaries, mangrove swamps, coastal lagoons, tidal channels, and coastal rocky or coral reefs. As with external morphology, preferred habitat of the Indo-Pacific Humpback Dolphin varies throughout its distribution. Individuals in waters off Australia are generally found in shallow waters around islands, reefs, or reef lagoons. Off India and China, they are found mainly in estuaries and deep-water channels. In waters of the Arabian and African regions, they are usually found in estuarine and near-shore waters with rockier substrates.
Food and Feeding. Feeding behavior of the Indo-Pacific Humpback Dolphin appears to be very opportunistic. They feed on a variety of near-shore estuarine and reef-associated fish. In some parts of their distribution, they occasionally feed on cephalopods and sometimes, but rarely, crustaceans. Important prey include fish in the families Sciaenidae , Mugilidae , Apogonidae , Clupeidae , Haemulidae , and Sparidae .
Breeding. Mating and breeding of the Indo-Pacific Humpback Dolphin appear to occur throughout the year, although late spring and summer tend to be peak breeding periods. Gestation lasts 10-12 months. Birth interval is thought to be ¢.3 years. Lactation may last more than 24 months. In South Africa, males reach sexual maturity later (12-13 years) than females (10 years). Female Indo-Pacific Humpback Dolphins in waters off Hong Kong reach sexual maturity at 9-10 years of age. Longevity is thought to be up to 40 years and does not seem to differ between sexes.
Activity patterns. Typical daytime behavior of the Indo-Pacific Humpback Dolphin includes foraging, socializing, traveling, and resting. They swim slowly (5 km/h) and surface briefly for up to one minute, with dives lasting up to five minutes. The diel pattern of the Indo-Pacific Humpback Dolphin varies throughout its distribution. In Algoa Bay, peak activity occurs in morning and evening at high tide, whereas in Maputo Bay, Mozambique, they are observed more often in the afternoon. Aerial behavior is not uncommon and includes leaps and somersaults.
Movements, Home range and Social organization. The Indo-Pacific Humpback Dolphin is commonly found alone or in small groups of ten or fewer individuals. In some cases in Chinese waters, as many as 30-40 individuals have been seen together, and in Arabian and Malaysian waters, groups of more than 100 individuals have been reported. Seasonal variations in group size have been detected in populations from Algoa and Plettenberg Bays in South Africa, where group size increases in summer and winter. This variation does not seem to occur among Indo-Pacific Humpback Dolphin in waters off Australia, Hong Kong, or Mozambique. All age classes can be found in larger groups, with adults generally making up one-half to two-thirds of the group. The Indo-Pacific Humpback Dolphin has been observed in mixed groups with the Indo-Pacific Bottlenose Dolphin ( Tursiops aduncus ), the Common Bottlenose Dolphin (7. truncatus ), the Southern Right Whale (Eubalaena australis ), the Snubfin Dolphin ( Orcaella heinsohni ), and the Afro-Australian Fur Seal (Arctocephalus pusillus). Social vocalizations of Indo-Pacific Humpback Dolphins are very important in the murky waters they inhabit. Frequencies of vocalizations from individuals in Australian waters are 0-6-200 kHz. Photo-identification and genetic studies have indicated that the social structure of some populations of Indo-Pacific Humpback Dolphins is quite fluid; associations are shortterm and it is uncommon for individuals other than mother—offspring pairs to have strong bonds. This social structure tends to occur in waters off South African. In Maputo Bay, Mozambique, more long-term associations are observed among individuals other than mother—offspring pairs. In Pearl River Estuary off Hong Kong, there are two communities of Indo-Pacific Humpback Dolphins, one with more long-term associations than the other. Allomaternal care of offspring has been suggested in populations of Indo-Pacific Humpback Dolphins off South Africa and Taiwan. The Indo-Pacific Humpback Dolphin does not undertake any large-scale migrations, but seasonal changes in distribution have been detected in South Africa, Mozambique, and Hong Kong. During the rainy season, Indo-Pacific Humpback Dolphins in Pearl River Estuary range more widely, with increased freshwater input influencing the delta.
Status and Conservation. CITES Appendix I. Classified as Near Threatened on The IUCN Red List. The eastern Taiwan Strait subpopulation is listed as Critically Endangered. Presently, there is no reliable global abundance estimate for the species. However, some estimates of Indo-Pacific Humpback Dolphins in specific areas include ¢.1200 individuals in the Pearl River Estuary of southern China; ¢.80 individuals in Xiamen, China; c.h4=74 individuals in the eastern Taiwan Strait; ¢.237 individuals in the waters around Leizhou Peninsula, southern China; ¢.34-54 individuals in Cleveland Bay, Australia; c.119-163 individuals in Moreton Bay, Australia; c.450 individuals in Algoa Bay, South Africa; ¢.170-244 individuals in Richard’s Bay on the KwaZulu-Natal coast, South Africa; c.105 individuals in Maputo Bay, Mozambique; ¢.60 individuals in Bazaruto Archipelago, Mozambique; and ¢.58-65 individuals in the waters off Zanzibar. For the distinct and isolated eastern Taiwan Strait population, the best estimate is fewer than 75 individuals. The species as a whole is likely in decline. The most serious threats are fisheries catch (incidental and direct) and habitat loss and degradation. The Indo-Pacific Humpback Dolphin is often caught in gillnets, trawls, and anti-shark nets. Vessel collisions have had a large impact off Hong Kong, where 14% of documented strandings in 1993-1998 were attributed to boatstrikes. Environmental contaminants are also a major threat. In Hong Kong, concentrations of organochlorines in cetaceans are significantly higher than in other parts of the world. High levels of neonatal mortality (53% ofstrandings) in Hong Kong may be related to high organochlorine levels. Indo-Pacific Humpback Dolphins dying from oil-related causes in the Persian Gulf have high tissue concentrations of organochlorines and other contaminants. Mercury levels in Indo-Pacific Humpback Dolphins off Hong Kong were an order of magnitude higher than in their prey and, in some cases, were high enough to be considered detrimental to dolphins’ health. These contaminants are known to cause pathological problems, such as immunosuppression and reproductive failure, in other marine mammals. Underwater noise from industrial activities, including pile-driving and dredging, threaten to cause acoustic disturbances. In some areas of Africa and Madagascar, Indo-Pacific Humpback Dolphins are intentionally killed for human consumption. Other threats include noise disturbance from military sonar and seismic surveying, overfishing of prey species, reduction offreshwater flow from upstream damming, and effects of climate change on habitat and prey availability.
Bibliography. Barros et al. (2004), Chen Tao et al. (2010), Cockcroft (1989), Dungan et al. (2012), Jefferson (2000), Jefferson & Karczmarski (2001), Jefferson, Hung et al. (2012), Jefferson, Webber & Pitman (2008), Parra & Jedensjo (2009), Parra & Ross (2009), Reeves, Dalebout et al. (2008b), Ross, G.J.B. et al. (1994), Ross, PS. et al. (2010), Wang, Hung & Yang Shihchu (2004), Wang, Hung, Yang Shihchu, Jefferson & Secchi (2008), Wang, Yang Shihchu, Fruet et al. (2012), Wang, Yang Shihchu & Reeves (2007).
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