Ganges River Dolphin

(Platanista gangetica gangetica)

INFORMATION AND CHARACTERISTICS.

It is one of two subspecies of the South Asian river dolphin (Platanista gangetica), and it has the title of the national aquatic animal of India, where is also called Ganges susu or shushuk.

HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.

The Ganges River dolphin and its closely related subspecies, the Indus River dolphin, have an appearance quite different from that of oceanic dolphins. Specifically, this species has the following characteristics:

Morphology.
It has a robust body with an asymmetrical skull, a protruded front, and a very flexible neck. Its long snout measures almost 20 percent of its body length and in adult females is even longer than that of the males. It has a small crest on the melon.

The dorsal fin is a little triangle with a broad base, and the longer pectoral flippers are flat. Its eyes are tiny.

Order: Cetacea
Family: Platanistidae
Genus: Platanista
Species: Platanista gangetica

Weight and size.
An adult has a length between 2 and 2.2 meters, and it has an approximate weight of 51-89 kilograms.

Skin Coloration.
The body has a dark gray or brown color, with a lighter color in the ventral area.

Distinctive characteristics.
It’s hard to differentiate a Ganges River dolphin from an Indus River dolphin, but the former species has a slightly longer tail than that of its relative.

WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.

The Ganges River dolphin distribution is limited to the east of India. It inhabits the freshwater system Ganges-Brahmaputra-Megna (GBM) and the Karnaphuli-Sango river systems, and their tributaries, which run through Nepal, Bhutan, and Bangladesh.

It Inhabits large sections of these rivers or their tributaries from the tidal zone to the foothills of the Himalayas, the Cachar Hills (District of India) and the Garo Hills of Meghalaya (Indian state). During the flooding season, this dolphin leaves the main canals and reach the temporary tributaries and flooded lowlands.

It is most frequently found in bodies of countercurrent water located between the convergence of channels and meanders (pronounced curves) and occasionally go to channels and reservoirs. Their habitat has a depth of 3 to 9 meters, and water temperatures between 8 and 33 Celsius degrees.

WHAT DO THEY EAT? DIET AND EATING HABITS.

The Ganges River dolphin has a carnivorous diet which includes a large variety of fish and invertebrate animals; perhaps it is also capable of consuming birds and turtles. These are some of their usual prey:

– Common carp.
– Gobio.
– Prawn.
– Freshwater sharks.
– Mahseer fish (Family Cyprinidae).
– Shrimp.

Although it has visible teeth in the jaws, it does not use them to chew but to hold their prey firmly. Its eyes are not useful to find food because in the muddy waters of its habitat they are not required, that is, it is an animal functionally blind, so it uses echolocation to detect prey.

This dolphin usually swims with a fin touching the riverbed to feel the sediments since animals hide there. Its snout is very useful for this. Once it finds a suitable prey, it holds the victim with the jaws and begins to swallow it whole starting from the head so that the scales (if the prey has them) do not hurt its throat.

It does not always look for food at the riverbed. Its most common practice is finding a school of fish near the surface and drag them to the bottom to eat them.

HOW DO THEY BEHAVE? BEHAVIOR.

The maximum speed that this dolphin reaches when swimming in its natural habitat is 27 kilometers per hour.

This dolphin has a shy, quiet and rather passive behavior. It swims alone or with 1 or 2 more individuals (pods may have 2-10 members) and rarely gather in large groups although some people report sightings of groups with up to 30 members. It is probably a semi-gregarious and territorial animal since sometimes it chases other dolphins aggressively. Their leaps out of the water are related to reactions to aggressions or external disturbances.

The primary function of the sense of echolocation in this species is searching for food rather than communicating. An unusual behavior observed in this species is the habit of swimming sideways, especially to the right. The reason is unknown. The maximum speed that reaches when swimming in its natural habitat is 27 kilometers per hour.

During the rainy season, this dolphin ventures into the tributaries of the river and returns to the main canals in the winter.

HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.

The Ganges River dolphin mates throughout the year and not in any specific season. The first breeding occurs between six and ten years of age and females give birth once every 2 or 3 years. It is a relatively large interval that, together with the late maturation, produce a low natality rate that does not contribute to increasing the number of individuals in the wild.

It is not known the process of courtship and mating, and a calf is born 8 to 12 months after the intercourse more frequently between December and January and between March and May. Maternal care is presumed to be similar to that of other dolphin species, but in this case, after weaning (1 year after birth), the offspring do not maintain ties with its mother.

WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.

Conservation status: “Endangered.”

As is frequently the case in the world of dolphins, the greatest threat to this species are humans who, looking for their meat and oil, have hunted them for many years putting them close to extinction.
According to the Red List Of the International Union for the Conservation of Nature (IUCN), this subspecies has a conservation status of endangered.

These dolphins do not have many predators in their habitat, so most of their threats are anthropogenic like:

– Dam construction.
These structures separate different populations of the same species which reduces the genetic diversity and the amount of mature individual available to mate.

– Bycatch.
They are sometimes trapped or entangled in fishing nets and other devices which are not intended to hunt these cetaceans.

– Pollution.
The contamination of the Ganges river comes from chemicals, garbage, residual waters and industry spills.

There are less than 2,000 Ganges dolphins left in the wild and a few time to help them survive in this challenging context. But the cause is not entirely lost, as the Indian Wildlife Protection Act looks for the protection of this species as a priority. Also, international organizations such as the WWF (World Wide Fund for Nature) have established programs to move from theory to practice and reduce the degradation of this dolphin’s habitat.

References

http://www.iucnredlist.org/details/41758/0

Rashmi Sanghi. Our National River Ganga: Lifeline of Millions. Springer Science & Business Media,  2013.

http://s3.amazonaws.com/academia.edu.documents/46348097/Sources_and_Accumulation_of_Butyltin_Com20160608-24155-1njpezf.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1489183099&Signature=0jehfoy3PH4ix9VZ15G6QKFQMVU%3D&response-content-disposition=inline%3B%20filename%3DSources_and_accumulation_of_butyltin_com.pdf

Mammals in the Seas: Small cetaceans, seals, sirenians and otters. Food & Agriculture Org., 1978.

http://animaldiversity.org/accounts/Platanista_gangetica/

Indus River Dolphin

(Platanista gangetica minor)

INFORMATION AND CHARACTERISTICS.

The Indus River dolphin, Indus blind dolphin or locally known in Pakistan as Bhulan, is one of two subspecies of the South Asian river dolphin (Platanista gangetica).

This toothed cetacean is closely related to the Ganges dolphin (Platanista gangetica gangetica), and with this dolphin, they form a small group of surviving dolphins belonging to a family of river cetaceans.

HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.

Despite its great physical resemblance to the Ganges River dolphin, this subspecies differs from the other by some physical characteristics.

Morphology.
It has a sturdy and fusiform body, with a long snout that is about 20 percent of the total length of its body. This structure is flattened and thin but broad at the tip and contains many large, visible teeth. It has large flippers and a wide but thin tail. Its flippers are approximately 18 percent of their body length.

Order: Cetacea
Family: Platanistidae
Genus: Platanista
Species: Platanista gangetica

Its dorsal fin is poorly developed and appears to have only a triangular crest or a hump on the back. It has a broad forehead that rises from the base of the snout. Its eyes are small and useless because it swims in muddy water, so it is blind, but this does not deter them from detecting prey with their echolocation sense.

Their teeth are visible even if their mouth is not open, they can insert and overlap other teeth, and those in the lower jaw are longer and curved.

Weight and size.
It has sexual dimorphism since females are larger than males. The latter have a length of approximately 2 to 2.2 meters and the former, 2.4 to 2.6 meters on average.

Skin Coloration.
Without a uniform coloration throughout its body, its skin usually has a brown or gray color that turns pink in the belly. The upper part of its body is darker than the bottom.

Distinctive characteristics.
Possibly its long snout is the most outstanding feature. When a female reaches sexual maturity, its snout abruptly grows until it is longer than that of the males.

WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.

The Indus River dolphin, as suggested by its name, inhabits the river of the same name in Pakistan, in an area of ​​690 kilometers. In the past, these cetaceans swam freely along the 3,500 kilometers of the river, but the problems associated with the growth of human population and its activities confined them to a small part of the river. There are populations between the dams of Sukkur, Guddu, Chashma and Taunsa.

It inhabits the deepest part of the river channel, at the confluences with other bodies of water, in shallow areas (about 30 meters) and at temperatures between 8 and 33° Celsius.

WHAT DO THEY EAT? DIET AND EATING HABITS.

The Indo River dolphin has a carnivorous diet being fish the principal part of its food. Herring, common carp, Gobio, Mahseer fish, and catfish are some of the species included in the diet of Platanista gangetica minor. Additionally, this dolphin eats prawns, clams, and shrimp, consuming about 1 kg of food per day.

In the same way as oceanic dolphins, the Indo River dolphin uses echolocation to search for food, but this dolphin relies completely on this sense for this as it is practically blind. It submerges for 30 to 90 seconds and with the help of its long snout explores the riverbed trying to find something edible that is hiding between the rocks or in the mud. Sometimes, its feeding activities are carried out in coordinated groups.

HOW DO THEY BEHAVE? BEHAVIOR.

It is a dolphin not commonly seen by humans and therefore, little studied. Evidently lonely, it swims alone or in small groups of 2 or 3 individuals in shallow waters. Like its relative the Ganges River dolphin (Platanista gangetica gangetica), it usually swims sidewards.

It uses its sense of echolocation to perceive its surroundings, to look for food and to communicate with its companions. In the latter case, it emits constant vocalizations of 15 to 150 kilohertz and receives sounds in the form of periodic pulses.

HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.

Males and females can mate at any time of the year, and they do not have a specific breeding season. Both reach sexual maturity between six and ten years of age or until they reach a length equal or greater than 1.7 meters.

Once they mate, the pregnant female waits up to 11 months, which is the maximum time that the gestation period of this species lasts, although it may be as short as eight months. After that, one calf is born with a length ranging between 0.7 and 0.9 meters, this is, almost half the size of the mother.

The information about their reproductive habits is very scarce if compared with other species because aspects such as courtship or breeding are not exactly known. The maternal care extends for one year until the calf reaches that age. In the wild, its life expectancy is up to 30 years.

WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.

Conservation Status: Endangered (EN)

Something sorrowful is happening with the Indus River dolphin: There are only about 1,100 individuals left in the wild, mainly in the part of the Indus River in Pakistan, which makes this species one of the most threatened in the world. Why is this happening?

– Human development.
The construction of dams and dikes segments the populations reducing the mature individuals to mate, but it also reduces their habitat because they cannot move freely through these structures.

– Bycatch.
They commonly get trapped in gillnets, longlines or other fishing gear intended to catch fish.

– Direct hunting.
Some people kill them for their meat and oil or to use them as bait or even to prepare alternative medicines.

– Pollution.
Habitat contamination due to industrial, agricultural and domestic activities.

– River traffic.
The high traffic in the river cause collisions with the propels of boats that injure them severely.

According to the Red List of the International Union for Conservation of Nature (IUCN), this species is in danger of extinction (Endangered). The World Wide Fund for Nature (WWF) has been proactive and has developed strategies to rescue dolphins trapped in fishing gear; They share this task with the United Nations Development Programme.

References

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

Rashmi Sanghi. Our National River Ganga: Lifeline of Millions. Springer Science & Business Media,  2013.

http://www.fisheries.noaa.gov/pr/species/mammals/dolphins/indus-river-dolphin.html

http://www.iucnredlist.org/details/41757/0

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