(Tursiops aduncus)

INFORMATION AND CHARACTERISTICS.

Before 1998, the Indo-Pacific bottlenose dolphin was considered a member of the species Tursiops truncatus (Bottlenose dolphins) because of their incredible physical resemblance. After several studies, scientists realized that this species is smaller and has more teeth than Tursiops truncatus, so in 1998 the Indo-Pacific bottlenose dolphin became a separate species according to its genetic and morphological characteristics.

Further research found that this dolphin is even more related to the genus Stenella and the genus Delphinus than to the bottlenose dolphin, but there are no changes in its taxonomy yet.

Order: Cetacea
Family: Delphinidae
Genus: Tursiops

HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.

The Indo-Pacific bottlenose dolphin has a similar physical resemblance to the common bottlenose dolphin. Both species have homodont denture and conical dental pieces with a diameter of 1 centimeter. Compared to other mammals, Tursiops aduncus has more red blood cells and 29 times more myoglobin (muscle protein).

Morphology.
It has a fusiform body, a large dorsal fin, small head, and face that narrows from the base. The length of its skull is shorter compared to the bottlenose dolphin.

Size and weight.
It is a small dolphin whose average length is 2.6 meters being males slightly larger than females. Its weight oscillates around 230 kilograms.

Skin Coloration.
The dorsal part of its body has a dark gray color that extends to the sides while the ventral region is whitish. Its pectoral flippers are also dark gray.

Distinctive characteristics.
One of the features that indicate that it is an Indo-Pacific dolphin is the presence of small spots in the ventral area in adults who are sexually mature although some individuals lack them.

WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.

The Indo-Pacific dolphin has a distribution in the tropics and subtropics of the Indo-Pacific as its name suggests. It inhabits from the west of South Africa to the southern part of Japan and the north, east and west of Australia including the Red Sea, the Persian Gulf, the Solomon Islands and the Indo-Malay Archipelago.

The waters of the countries hosting these dolphins are Australia, Bangladesh, China, Cambodia, Djibouti, Eritrea, Indonesia, China, Egypt, Iran, Brunei, Iran, Kenya, Madagascar, Malaysia, Mozambique, Oman, Pakistan, Arabia South Africa, Sri Lanka, Taiwan, Tanzania, Timor-Leste, Thailand, United Arab Emirates, Philippines, Japan, Solomon Islands, New Caledonia, Vietnam, Yemen and New Guinea.

This dolphin inhabits areas near the shores within the continental shelf in waters with depths less than 300 meters and around the islands. Its habitat varies depending on the tides and the season but includes estuaries, coral reefs and surface waters at high seas, so it tolerates both saltwater and brackish water.

87 percent of their food is made up of about 50 species of fish.

WHAT DO THEY EAT? DIET AND EATING HABITS.

Tursiops aduncus feeds on bony fish as well as cephalopods. A study of its feeding habits showed a preference for about 50 species of fish and three species of squid, that is, 87 percent of their diet is composed of the former, and 13 percent corresponds to these cephalopods. They also consume a minimum amount of crustaceans.

The species that make up their favorite foods are the
– Striped threadfin (Polydactylus plebeius).
– Chub mackerel (Scomber japonicus).
– Kaup’s arrowtooth eel (Synaphobranchus kaupii).
– Yellowtail emperor (Lethrinus crocineus).
– Common Cuttlefish (Sepia Officinalis).
– Broadclub Cuttlefish (Sepia latimanus).
– Bigfin reef squid (Sepioteuthis lessoniana).

Among others.

It commonly feeds alone although sometimes cooperates with other dolphins to obtain prey. To do this, they perform several dives for short intervals. If it is in very shallow waters it can a) drag the fish down and hit them against the sand with its tail or b) chase the prey to the surface to kill it and eat it.

HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.

Females reach sexual maturity a few years earlier than males. The former can start reproducing at seven years, but the latter begin up to nine years. Mating and births occur more frequently during the spring and summer months.

The males of these dolphins show a strange behavior in mammals: they build alliances by integrating groups of 2 or 3 members that allow an easier pairing with a particular female. On the other hand, single males tend to protect a pod of females.

The Indo-Pacific bottlenose dolphins are polygamous. A male knows that a female is already sexually mature when she shows spots on her skin. When they are ready, both copulate for a few seconds with the bellies united in the same direction.

The gestation period lasts about 12 months, after which a single calf is born that weighs between 9 and 21 kilograms and measures 0.8-1.1 meters in length. From the first seconds of life, the calf can swim following its mother. Calves are weaned when they are 2-8 years old, and mothers can get pregnant every four years.

HOW DO THEY BEHAVE? BEHAVIOR

Like most dolphins, it is a highly social species that groups with 5-15 peers, yet they are shyer than common bottlenose dolphins. Associations are formed according to size, age, and gender and can sometimes meet with other species of dolphins.

They are mostly diurnal and sedentary because they remain in their birth zones throughout their lives. They have a high learning ability, and it is not strange to see them playing. They have an excellent auditory capacity and emit a kind of individual whistles that identify them with the other members of the same pod or the same species.

WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.

Conservation Status: “Data Deficient.”

Their natural predators are mainly white sharks (Carcharodon carcharias), tiger sharks (Galeocerdo cuvier), dusky sharks (Carcharhinus obscurus) and other species of shark as well as killer whales (Orcinus orca).

Since it is used to live near the coasts, it is more susceptible to the dangers of human activities and their consequences: degradation of its habitat, direct hunting, and bycatch. Industries use parts of their body to market the meat and produce oils and lubricants. Also, they are common animals in aquariums, so they are the target of the tourism businesses.

To date, there is no information on its conservation status since the International Union for Conservation of Nature includes it in the category “Data Deficient.” There are no specific conservation strategies for this dolphin.

References

http://www.conabio.gob.mx/institucion/cooperacion_internacional/TallerNDF/Links-Documentos/Casos%20de%20Estudio/Mammals/WG5%20CS2.pdf

http://www.cms.int/reports/small_cetaceans/data/t_aduncus/t_aduncus.htm

https://en.wikipedia.org/wiki/Indo-Pacific_bottlenose_dolphin

Jefferson, Webber, Pitman. Marine Mammals of the World: A Comprehensive Guide to Their Identification. Academic Press, 2015. Page 244.

]]> https://www.dolphins-world.com/irrawaddy-dolphin/ Thu, 27 Apr 2017 05:27:30 +0000 http://www.dolphins-world.com/?p=98 Author of the picture: Dan Koehl.

Irrawaddy Dolphin Facts

(Orcaella brevirostris)

INFORMATION AND CHARACTERISTICS.

The Irrawaddy river dolphin is a species that belong to the group of oceanic dolphins. Paradoxically, it is not a dolphin exclusively of freshwater. It is closely related to the Orca (Orcinus orca), and it is one of the most threatened extant dolphins.

In Laos, the inhabitants have the belief that humans can reincarnate in these dolphins.

Order: Cetacea
Family: Delphinidae
Genus: Orcaella

HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.

The Irrawaddy dolphin is a singular-looking dolphin, whose body differs from the stereotype of the best-known dolphins. Physically it is similar to the beluga whale (Delphinapterus leucas), another toothed cetacean and marine mammal.

Weight and size.
The species exhibits sexual dimorphism since the male tends to be larger and heavier than the female. An adult has a weight of approximately 130 kilograms and a length of 2.3 meters.

Morphology.
The body of this dolphin is very robust. It has a rounded head and a very bulging forehead that extends from above the mouth. Its dorsal fin at the back end is small and has a triangle shape while the pectoral flippers are long, wide and also triangular. It has no heart sphincter, and as with other dolphins, its stomach splits into several compartments.

Skin Coloration.
The skin in the dorsum and the sides has a blue or gray color, but the color in the ventral area is slightly lighter as well as in the last part of the back.

Distinctive Characteristics.
This dolphin lacks a beak, and since its neck is very flexible, it has wrinkles behind the head as a result of this capability.

WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.

The Irrawaddy dolphin thrives in tropical and subtropical waters of the Indo-Pacific region on and near shallow coastal waters. It inhabits Southeast Asia from Borneo and the islands of the Indonesian Archipelago to Papua New Guinea. Three subpopulations live in freshwater rivers:
– Ayeyarwady in Burma,
– Mahakam in Indonesia
– Mekong in Laos.

They also live in two brackish water systems:
– Chilika Lake in India
– Songkhla Lake in Thailand.

The countries where this species dwells are Vietnam, Cambodia, Singapore, Thailand, Indonesia, Burma, Laos, Philippines, Bangladesh, Brunei, India, and Malaysia.

It inhabits coasts, rivers, estuaries, deltas and large lakes of its distribution zone, regularly near the mangroves. Almost all sightings have happened not more than 1.6 kilometers away from the coast and a less than 5 kilometers, and apparently, they do not usually live in deep waters.

WHAT DO THEY EAT? DIET AND EATING HABITS.

It is a carnivorous cetacean that feeds on several species of cephalopods, fish, crustaceans and fish eggs. It establishes a strategy of cooperation in groups composed of 6-15 dolphins. To hunt, they can spit water to attract more fish and even hit large species with their lower jaw, perhaps in an attempt to play before eating.

In some regions of Asia these dolphins fish in cooperation with local fishers which call them, and surprisingly the dolphins come swimming in semicircles and hauling the fish to the surface. Thus both parties benefit since the dolphins feed themselves with the fish stunned or trapped in the edges of the boat.

HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.

There is not much information about the mating habits of the Irrawaddy dolphin. Individuals reach sexual maturity at around 3-9 years of age and the mating season is variable. For example, in the northern hemisphere dolphins mate from December to June and births occur between June and August.

The female delivers one single offspring after a gestation period of 14 months. Researchers assume that, just as in other species, males mate with and compete for several females.

At birth, the offspring weigh about 10 kilograms and measure about 1 meter. Six months later they are already able to consume fish, and after one year and a half, they are usually completely weaned.

HOW DO THEY BEHAVE? BEHAVIOR

This dolphin shows high sociability inside and outside its pod because its groups are composed of 5-57 members but also occasionally meet with other species of dolphins. The most common practice is that they live in small groups of 3 to 6 members.

This species makes slow movements and has less activity than other dolphins; it usually breathes taking out only the head out of the water. In the same way, they take a look around: with the head as the only visible point. However, it has been seen jumping, making bubbles and hitting the water with its flippers and tail.

Their territories cover about 35 kilometers in length. Individuals from eastern Borneo make daily migrations to the Mahakam River but always return to their area at night. For their part, those living in Indonesia move into the River tributaries at high tide and to the river when the tide is low.

WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.

There are no identified natural predators of this species, and only the humans represent a threat to them.

The low reproduction rate and the human-related threats contribute to the rapid decline of the Irrawaddy dolphin populations and the danger of extinction in some areas. There are no known natural predators of the species, so it is essential that the humans stop threatening this dolphin.

Individuals are often trapped in gillnets or die after dynamite explosions when fishers use such method. It is also gets electrocuted with nets used in electric fishing. To make things worse, water pollution and dam construction destroy and negatively modify their habitat and puts them in danger.

Fortunately, this dolphin under protection in Laos, Vietnam, and Cambodia, and Bangladesh, India, Laos, Malaysia, Burma, and Thailand banned its hunting. In fact, in Burma, there is a reserved area of about 74 kilometers of the river Ayeyarwady.

The Whale and Dolphin Conservation (WDC) organization dedicated to the conservation of whales, dolphins, and porpoises created an Operation Plan for the Conservation of the Irrawaddy Freshwater Dolphin Populations given the potential extinction problem in Southeast Asia.

References

https://en.wikipedia.org/wiki/Irrawaddy_dolphin

http://www.cms.int/reports/small_cetaceans/data/O_brevirostris/O_brevirostris.htm

Jefferson, Webber, Pitman. Marine Mammals of the World: A Comprehensive Guide to Their Identification. Academic Press, 2015. Page 183.

https://www.worldwildlife.org/species/irrawaddy-dolphin

(Sousa chinensis)

INFORMATION AND CHARACTERISTICS.

The Chinese white dolphin is a variety of the Indo-Pacific Humpbacked Dolphin, although some consider it a subspecies of the latter. It is a species of dolphin characterized by the pink color of the skin that some individuals may have. The first time it was seen dates back to the seventeenth century.

Two types of the Indo-Pacific Humpbacked Dolphin are known (Sousa chinensis and Sousa plumbea), although the taxonomy of Sousa chinensis is not yet clear as some scientists consider it a variety but others a subspecies. If the latter, its scientific name is Sousa chinensis chinensis.

Order: Cetacea
Family: Delphinidae
Genus: Sousa

HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.

The physical characteristics of the individuals of this species vary slightly according to the geographic region in which they live. For example, male specimens from the coasts of some areas have sexual dimorphism that other populations do not have.

Morphology.
It has a hydrodynamic body with a long, slender beak and a dorsal fin with a fat hump. Dolphins inhabiting eastern waters have a short dorsal fin whose broad base descends gradually over the dorsum. In contrast, individuals from western territories have a shorter and curved dorsal fin. The hump represents between 5 and 15 percent of its total length.

Size and weight.
It is a small dolphin; its length is between 2 and 2.8 meters. Its weight is between 150 and 200 kilograms.

Skin Coloration.
Perhaps, if it were not for the genetics, the Indo-Pacific Humpbacked Dolphin could not be recognized because of the color variability depending on the geographic region it inhabits. The adult specimens of the Chinese coasts have a pinkish appearance thanks to the blood vessels underneath, not because the skin has that color. In contrast, young individuals are gray.

Distinctive characteristics.
The main distinctive feature of the Chinese white dolphin is the hump on the dorsal fin and the pink color that many specimens present on the skin.

WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.

It is distributed only in waters of the Indian and Pacific Ocean, from northern Australia to eastern China as well as in the Indo-Malayan archipelago, the Bay of Bengal and the Gulf of Thailand. The plumbea type is found on the coasts of the Indian Ocean while the chinensis is mainly in the Pacific.

They prefer to inhabit warm and temperate waters with temperatures above 15° C and an average depth of 20 meters. They live on or near open coasts, bays, estuaries, mangroves, sandbanks, reefs, coastal lagoons, and river mouths.

Chinese white dolphin – Sousa chinensis chinensis

WHAT DO THEY EAT? DIET AND EATING HABITS.

This dolphin prefers coastal fishes and those who live in reefs, littorals, and estuaries. Their prey includes cephalopods and crustaceans on few occasions.

It searches for opportunistic food in shallow waters, near the bottom of the ocean. If the tide is high, it ventures to areas with abundant food. In several areas of Australia, it has been seen following boats that catch fish and shrimp, to feed on discarded animals.

HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.

Females reach sexual maturity at 9-10 years of age and males later, as they reach sexual maturity between 12 and 13 years.

The reproduction season is during the months of spring and summer although it can extend until the autumn. There is little information about the reproductive habits of this dolphin and much less about its courtship methods. Studies and observations indicate that this species has as its primary reproductive strategy searching for a partner to mate.

+ Gestation period: 10 to 12 months.

After a gestation period of ten to twelve months, the female gives birth to a single offspring measuring 1 meter in length that is the object of dedicated maternal care even after weaning, which occurs when the calf is about two years old. However, oddly, the maternal care does not take place in individuals living on the coasts of South Africa (Plumbea type) and Hong Kong.

HOW DO THEY BEHAVE? BEHAVIOR

The Chinese white dolphin shows a behavior slightly less social than other species because it has been seen several times swimming alone. This does not mean that they do not form pods, but these usually have less than ten members and occasionally equal to or larger than 25 individuals. In the same way, the relationships between members are not close except fo those of mothers with their offspring.

This species can stay more than 4 minutes underwater without surfacing. Sometimes it jumps out of the water and hits the surface with its flippers, but do not perform jumps and stunts frequently. These dolphins usually avoid boats unless they are fishing boats. In such cases, they can be seen next to other species of dolphins and even other animals like whales and gulls.

It communicates by whistles and squeals, and to a lesser extent by clicks. On the other hand, it is considered a migratory animal that travels more than 120 kilometers away from home. This occurs mainly in summer in regions close to the African continent (Plumbea type)

WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.

Conservation Status: Near Threatened.

Sharks are the only known predators of this dolphin, although some think that they are also victims of killer whales (Orcinus orca), there are still no reliable reports on this fact.

Its main threats are related to anthropogenic activities that also endanger the lives of other dolphins. They are:

– The intentional catch for their meat and oil.

– Bycatch with gillnets.

– Habitat contamination.

– The decrease in the number of fish they feed on and fragmentation of the food chain.

– Coastal development that degrades its habitat (urbanization).

Because of the above, populations have declined drastically. It has a conservation status as “Near Threatened” on the Red List of the International Union for the Conservation of Nature.

References

http://www.bioone.org/doi/abs/10.1644/1545-1410(2001)655%3C0001:SC%3E2.0.CO;2

http://www.iucnredlist.org/details/20424/0

http://www.cms.int/reports/small_cetaceans/data/S_chinensis/s_chinensis.htm

Jefferson, Webber, Pitman. Marine Mammals of the World: A Comprehensive Guide to Their Identification. Academic Press, 2015. Page 227.

William F. Perrin, Bernd Würsig, J.G.M. ‘Hans’ Thewissen. Encyclopedia of Marine Mammals. Academic Press, 2009. Page 576.

There are only two species of bottlenose dolphins, the Common Bottlenose Dolphin (Tursiops truncatus) and the Indo-Pacific Bottlenose Dolphin (Tursiops aduncus).

Also, there are two recognized subspecies of Tursiops Truncatus:

The Pacific Bottlenose Dolphin (Tursiops Truncatus Gillii) which lives in the Pacific ocean.

The Black Sea Bottlenose Dolphin (Tursiops truncatus Ponticus) which lives in the Black Sea.