Platanista minor

Geographic Range

Indus River dolphins, Platanista minor , are found only in the Indus River in Pakistan. Platanista minor used to range throughout the river system, but the dolphins are now only found in the waters above the Kotri Barrage and below the Chasma, Trimmu, Sidhnai, and Islam Barrages. These human-created barriers, in addition to changes in rainfall patterns, have greatly limited the dolphins’ distribution.

• Biogeographic Regions
• oriental oriental
  • native native

Habitat

Platanista minor currently exists only in the freshwater Indus River. However, some paleontologists believe that river dolphins might have evolved from marine-dwelling relatives that eventually moved to estuaries and then rivers as seawater levels rose and fell during the Miocene. Though this species prefers water deeper than 3 meters, Indus River dolphins have special adaptations such as swimming on their sides that enable them to exist in shallower waters as well. The temperature of the water ranges from 8-33 degrees C.

• Habitat Regions
• freshwater freshwater

• Aquatic Biomes
• benthic benthic
• rivers and streams
• brackish water brackish water

Physical Description

Indus River dolphins are roughly the same color as the river, gray or brown, though they sometimes are lighter on their undersides. Their “beaks” are distinctively swollen at the tip and very long, reaching 20% of the length of their bodies, with large, visible teeth. In contrast to their “beaks”, their dorsal fins are rather small and reduced compared to other river dolphins. Large flippers and flukes, combined with long and remarkably flexible necks, probably help the dolphins navigate effectively. Platanista minor has external ears located below their eyes, but their eyes are very small and probably can only see shadowy, unclear images. Though Platanista minor and Platanista gangetica barely differ physically except for slight differences in tail lengths, the two species are distinguishable by their ranges. Platanista minor lives only in the Indus River system, while Platanista gangetica only inhabits the Ganges River system. Females are larger than males.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Reproduction

These dolphins probably do not mate seasonally, since calves are born at different times throughout the year. However, in a captive population of two females and a male in Switzerland, the male reportedly chased the females in the spring. Though scattered captive populations of Platanista minor exist, little is known about the mating behavior of any of the members of the Platanistidae family.

Platanista minor breeds throughout the year, and has a very long gestation period of 8-11 months. Though not mentioned in the literature, this species probably only gives birth to one offspring at a time since newborns are about a meter long when they are born, which is nearly half the length of an adult female.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

Little information is available about parental investment in Platanista minor , however, they most likely spend much time and energy on their offspring. Since females are pregnant for up to 11 months, newborns are about half the size of their mothers at birth, calves nurse up to a year after birth, Indus River dolphin offspring are probably very costly.

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

No data is available about the lifespan of Platanista minor . The dolphins probably live for a long time since they are relatively large and require 10 years to reach sexual maturity. However, recent poor water quality and reduced habitat might affect the current longevity of these animals in the wild. At least a few Indus River dolphins have been kept in captivity, however, their longevity data is unavailable.

Behavior

Platanista minor is described as mainly solitary, though the dolphins have occasionally been found in groups consisting of as many as 30 individuals. In general, however, Indus River dolphins travel in groups of no more than 3. These dolphins are equipped to swim on their sides in very shallow water if necessary, yet except for juveniles, Platanista minor rarely exhibits the stereotypical dolphin aerial leaping behavior. On the other hand, like other dolphins these animals are highly vocal and perceive their environment through echolocation. These sounds are mainly used to navigate while swimming, with a very small percentage used for communication.

• Key Behaviors
• natatorial natatorial
• motile motile
• solitary solitary
• social social

Home Range

No data is available about the home range of Platanista minor . Platanista gangetica , however, has been reported at densitites of 0.7-1.36 dolphins per kilometer. Perhaps Platanista minor also require about a kilometer of space each, though data is still absent to determine how far they travel. All that is known is that they appear to migrate seasonally along the river.

Communication and Perception

Indus River dolphins have extremely poor eyesight, perhaps since vision is nearly useless to navigate the murky rivers in which they live. They instead rely on echolocation to perceive their environment. Indeed, one of the common names for Platanista minor is “blind river dolphin”. Their external ears might help receive echolocation signals, which are intermittent pulses rather than continuous whistles. Though Indus River dolphins are very vocal, they use sounds for communication only about 5% of the time that they vocalize.

• Communication Channels
• acoustic acoustic

• Perception Channels
• tactile tactile
• echolocation echolocation
• chemical chemical

Food Habits

Indus River dolphins use their echolocation abilities combined with their highly toothed, long snouts to forage for many bottom-dwelling animals including fish and invertebrates. Platanista minor has been known to eat some species of catfish , herring , carp , gobies , mahseers, prawns , and clams . Captive individuals reportedly consume about a kilogram of food each day.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • eats other marine invertebrates

• Animal Foods
• fish
• mollusks
• aquatic crustaceans
• other marine invertebrates

Predation

Platanista minor has few if any natural predators, however, they are often hunted by local people.

Ecosystem Roles

Indus River dolphins each eat about a kilogram of benthic fish and invertebrates daily, it is not clear how strongly they impact any of their prey populations.

Economic Importance for Humans: Positive

Some people hunt Indus River dolphins for their meat and oil. People in some areas eat the dolphin meat, while others use it as a fishing lure, though studies indicate that fish flesh is just as effective. The dolphin’s oil is used for medicinal purposes, its supposed effectiveness as an aphrodisiac, and to rub on one’s skin.

• Positive Impacts
• food food
• source of medicine or drug source of medicine or drug

Economic Importance for Humans: Negative

There are no known adverse affects of Platanista minor on humans, though no one knows what might happen to the river ecosystem if these highly-endangered animals eventually become extinct. At the very least, however, Pakistan will lose part of its biodiversity forever if the country does not take steps to protect this unique dolphin.

Conservation Status

Platanista minor is a species of great concern, and a combination of human-created barriers such as dams and barrages, hunting, and a limited natural range have resulted in a dangerously-low total population of only several hundred individuals. These dolphins are classified as endangered, and have been so since the 1970's. Their extremely low population size may also restrict their gene pool, thus they might soon have many problems associated with low genetic variation within a population.

Other Comments

Some authors consider Platanista minor to be a subspecies of Platanista gangetica , others consider them the same species, and others consider them distinct species. Genetic analysis has not yet answered the taxonomic mysteries of the Platanistdae family.

Additional Links

Encyclopedia of Life

Contributors

Matthew Wund (editor), University of Michigan-Ann Arbor.

Rachel Bricklin (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

References

Biswas, S., S. Boruah. 2000. Ecology of the River Dolphin ( Platanista gangetica ) in the Upper Brahmaputra. Hydrobiologia , 430: 97-111.

Hamilton, H., S. Caballers, A. Collins, R. Brownell. 2001. Evolution of river dolphins. Proc. R. Soc. Lond. , 268: 549-558.

Herman, L. 1980. Cetacean Behavior: Mechanisms and Functions . New York: John Wiley & Sons, Inc..

Mann, J., R. Connor, P. Tyack, H. Whitehead. 2000. Cetacean societies: field studies of whales and dolphins . Chicago: University of Chicago Press.

Moreno, P. 2004. Ganges and Indus dolphins ( Platanistidae ). Pp. 13-17 in Grzimek's Animal Life Encyclopedia , Vol. Volume 15: Mammals IV, Second Edition Edition. Detroit: Thompson Gale.

Pilleri, G. 1974. Side-swimming, vision, and sense of touch in Platanista indi (Cetacea, Platanistidae). Experientia , 30: 100-104.

Reeves, R., A. Chaudhry. 1998. Status of the Indus River dolphin Platanista minor . Oryx , 32: 35-44.

Sinha, R. 2002. An alternative to dolphin oil as a fish attractant in the Ganges River: conservation of the Ganges River dolphin. Biological Conservation , 107: 253-257.

Smith, B., B. Ahmed, M. Edrise Ali, G. Braulik. 2001. Status of the Ganges river dolphin or shushuk Platanista gangetica in Kaptal Lake and the southern rivers of Bangladesh. Oryx , 35: 61-72.