Tursiops aduncus (Ehrenberg, 1833)

Russell A. Mittermeier & Don E. Wilson, 2014, Delphinidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 410-526 : 515-516

24.

Indo-Pacific Bottlenose Dolphin

Tursiops aduncus

French: Dauphin indien / German: Indopazifik-Tiummler / Spanish: Delfin mular indopacifico

Other common names: Indian Ocean Bottlenose Dolphin

Taxonomy. Delphinus aduncus Ehrenberg, 1833 ,

“Belhosse Isl., Dahalk Arch., Ethiopia.”

Taxonomy of 1. aduncus was widely disputed before evidence from studies of morphology, genetics, and osteology led to designation as a species in 2000. There are still taxonomic uncertainties within 7. aduncus , and more research is needed to determine if certain subpopulations, such as those in Western Australia, may be another distinct species. Recent mtDNA studies suggest that 7. aduncus is most closely related to Stenella frontalis , but osteological studies suggest a close relationship with 7. truncatus . I. aduncus inhabits highly variable environments over a wide distribution, which also contributes to current taxonomic uncertainty. Monotypic.

Distribution. Warm temperate to tropical Indo-Pacific waters, from South Africa in the W to S Japan and C Australia in the E, including Red Sea, Persian Gulf, Indo-Malay Archipelago, and Solomon Is.

Descriptive notes. Total length 270 cm (males); weight 230 kg (males). Males tend to be slightly larger than females.

Neonates are 85-112 cm long. Similar to the Common Bottlenose Dolphin ( 1. truncatus ), the Indo-Pacific Bottlenose Dolphin has robust body, moderate-length beak, and tall and slightly falcate dorsal fin. Dorsalfin, flippers, and flukes tend to be broader and larger relative to their body size than those of the Common Bottlenose Dolphin. The Indo-Pacific Bottlenose Dolphin also appears more slender, with longer and thinner beak,slightly less convex melon, and head with more pointed profile. Eye region also appears to bulge out laterally. Skin pigmentation, although relatively simple, can be variable. Ventral side is generally off-white to pale gray and transitions laterally and dorsally to medium to dark gray. Dorsally, this darker gray appears as a cape that extends back onto tailstock. Pale spinal blaze may be present in some individuals and extends to below dorsalfin. Dark spotting is distinctive feature of the Indo-Pacific Bottlenose Dolphin, which is rarely found on the Common Bottlenose Dolphin. These prominent black spots can be found on bellies of adult Indo-Pacific Bottlenose Dolphins. They vary in intensity, which increases with age. Pigmentation around mouth line and tip of beak tends to get paler with increasing age. Young offspring are paler than adults, and spotting is absent. The Indo-Pacific Bottlenose Dolphin does not have any clear sexual dimorphism. Each jaw contains 19-27 pairs of teeth.

Habitat. Tropical to warm temperate waters, occasionally in cooler waters (e.g. offJapan, northern China, southern Australia, and South Africa). Sea-surface temperatures where the Indo-Pacific Bottlenose Dolphin is found vary greatly between regions but are generally 20-30°C. Preferred habitats of Indo-Pacific Bottlenose Dolphins appear to be near-shore, continental shelf waters and areas with sandy or rocky bottoms, coral reefs, or seagrass beds. They are most abundant in waters less than 100 m deep but can be found in waters deeper than 200 m.

Food and Feeding. Primary prey of the Indo-Pacific Bottlenose Dolphin tends to be benthic and reef-dwelling fish and cephalopods in continental shelf waters. They also consume some pelagic and epipelagic species. Populations in waters of oceanic islands appear to consume mostly epi- and mesopelagic fish and cephalopods, although benthic crustaceans can make up a substantial proportion of the diet. Prey species usually belong to several families, including Belonidae , Mugilidae , Sciaenidae , Engraulidae , Sepioteuthidae, Sepiidae , Sepiolidae , Loliginidae , and Octopodidae . On rare occasions, Indo-Pacific Bottlenose Dolphins eat small benthic sharks. Some foraging techniques include tail slaps to flush out prey, carrying sponges (potentially to protect rostrum from rubbing against the ocean floor while foraging), and chasing prey onto beaches to catch them.

Breeding. Mating activity of the Indo-Pacific Bottlenose Dolphin can occur throughout the year, but it is most frequent in spring and summer. Gestation lasts c.12 months. Birth interval is commonly 3-6 years. Lactation lasts 3-5 years before offspring are weaned. Female Indo-Pacific Bottlenose Dolphins that lose a neonate early can become pregnant again soon afterward and give birth the next year. Females can lactate and be pregnant at the same time. Males generally reach sexual maturity earlier (10-15 years) than females (12-15 years). Maximum life span is c.40 years, but there is some evidence from tooth growth rings that individuals can live 50 years or more.

Activity patterns. The Indo-Pacific Bottlenose Dolphin is thought to dive a maximum of 200 m, and most dives last 5-10 minutes. Normal swimming speed is 1-4-4 km/h, but speeds of 16-19 km/h can be reached during high-speed bursts. Surface behavior consists mostly of traveling, milling around, feeding, resting, and socializing.

Movements, Home range and Social organization. The Indo-Pacific Bottlenose Dolphin usually travels in groups of 20-50 individuals, although groups of up to 2000 individuals have been reported in South Africa. Mean group size in Plettenberg Bay is thought to be 140 individuals. Group size tends to be larger when young offspring are present. Based on populations in regions that have been studied extensively, Indo-Pacific Bottlenose Dolphins tend to be year-round residents in fairly limited coastal habitats. Minimum home range is thought to be more than 200 km? with males tending to range more widely than females. Individual Indo-Pacific Bottlenose Dolphins in waters of Kyushu,Japan, have been recorded in both Oita Prefecture and Kagoshima Bay, which are hundreds of kilometers away from each other. Movement across deep oceanic waters has been reported, but it is unknown if such movements are common. The Indo-Pacific Bottlenose Dolphin has been observed in groups with a variety of other species of delphinids, including the Common Bottlenose Dolphin, the Indo-Pacific Humpback Dolphin ( Sousa chinensis ), the Spinner Dolphin ( Stenella longirostris ), the False Killer Whale ( Pseudorca crassidens ), and common dolphins ( Delphinus spp. ). Sex ratio of the Indo-Pacific Bottlenose Dolphin is about equal at birth, but there are more males at subadulthood and more females surviving to adulthood. Natal philopatry occurs in some regions. Social organization of the Indo-Pacific Bottlenose Dolphin can be best described as fission—fusion. Males can form small alliances (general 2-3 individuals) to challenge other groups of males for access to females. These groups may have long-term consistency, suggesting persistent relationships among cooperating males—an unusual social trait among mammals. Female Indo-Pacific Bottlenose Dolphins can also form cooperative groups for protection against predators, to raise young, and for avoiding male coercion.

Status and Conservation. CITES Appendix II. Classified as Data Deficient on The [IUCN Red List. Due to taxonomic uncertainty, total abundance of the Indo-Pacific Bottlenose Dolphin is currently unknown. Some estimates of abundance have been made in various regions of their distribution, including 520-530 individuals off KwaZulu-Natal, South Africa; 136-179 individuals off Zanzibar, Tanzania; 1200 individuals in the Persian Gulf; 400 individuals in Watch-of-No-Ground, Bangladesh; 218 individuals off western Kyushu,Japan; 169 individuals off Mikura Island, Japan; ¢.50 individuals in north-eastern Philippines; 1099 individuals off Queensland, Australia; 2000-3000 individuals in Shark Bay, Australia; and less than 100 individuals off south-western Taiwan. Overall population trend is currently unknown. The most severe threats to the Indo-Pacific Bottlenose Dolphin are direct and incidental catch and habitat degradation. Incidental catchesin gillnets and purse seines are of great concern throughout the distribution of the Indo-Pacific Bottlenose Dolphin. In the 1980s, up to 2000 individuals were caught per year during Taiwanese shark fishery operations in Australian waters. They have also been hunted for human consumption and shark bait in the Philippines, Taiwan, and east Africa. Until large-scale drive hunts were banned in 1990, the Indo-Pacific Bottlenose Dolphin was caught in the Penghu Islands, Taiwan, to supply aquaria and tourist resorts in Europe, Mexico, and Dubai. In 2003-2007, more than 100 Indo-Pacific Bottlenose Dolphins were taken from the Solomon Islands for the same purpose. Habitat degradation from expansion of coastal aquaculture operations, heavy industrialization, and coastal development reduces availability of suitable habitat for the Indo-Pacific Bottlenose Dolphin. With heavy industrialization comes the threat of environmental contaminants. Other threats include disturbance by whalewatching vessels, increased offspring mortality from dolphin-feeding tours, and noise disturbance from dolphin-watching tours, pleasure boating, and commercial vessels.

Bibliography. Hammond et al. (2008r), Hawkins & Gartside (2008), Jefferson et al. (2008), Mann et al. (2000), Perrin et al. (2007), Shirakihara et al. (2012), Wang & Yang Shihchu (2007, 2009), Wang et al. (1999, 2000).

Figures

On following pages: 33. Commerson’s Dolphin (Cephalorhynchus commersonii); 34. Chilean Dolphin (Cephalorhynchus eutropia); 35. Heaviside's Dolphin (Cephalorhynchus heavisidii); 36. Hector’s Dolphin (Cephalorhynchus hector).

Distribution. Warm temperate to tropical Indo-Pacific waters, from South Africa in the W to S Japan and C Australia in the E, including Red Sea, Persian Gulf, Indo-Malay Archipelago, and Solomon Is.