Sharks play an essential rol in the health of our oceans

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Did you know? Sharks that live in fresh waters only!

The bull shark (Carcharchinus Leucas) is known to swim in rivers, but it always returns to sea. But there are actually sharks, that  live in fresh water only. These  rare river sharks belong to the genus  Glyphis (family Carcharhinidae – requiem harks), but there could be other species as well, that are still undiscovered.  So far, five species have been documented:

Speartooth shark (Glyphis glyphis) at the Melbourne Aquarium, Bill Harrison

 

  • Borneo river shark, Glyphis fowlerae, living in North East Borneo, found only in the Kinabatangan river in Sabah. Status probably Critically Endangered, named after shark expert Sarah Fowler.
  • The Ganges shark, Glyphis gangeticus, from the river Ganges in India, Critically Endangered, population trend: decreasing
  • New Guinea river shark,  Glyphis garricki,, living in rivers in New Guinea, Critically Endangered, population trend: decreasing
  • Speartooth shark,  Glyphis glyphis, from Northern Australia, status: Endangered, population trend: decreasing
  • Irrawaddy river shark, Glyphis siamensis, from the mouth of the Irrawaddy river in Myanmar, critically Endangered, population trend: unknown. This shark is known only from a single 19th century museum specimen.

Glyphis gangeticus, an old illustratie by Muller and Henle, 1893

Not much is known of the ecology of river sharks. They have small eyes, and their teeth indicate that they are primarily fisheaters, adapted to hunt in murkey estuarine and river waters with limited visibility. It seems likely that hearing, smell and electroreception may play a more significant role in predation than sight. Nothing is know about their reproduction, but they are presumably viviparous. Maximum length is probably between 200 and 300 cms.

Populations are decreasing due to habitat loss and overexploitation. This genus lives mostly in mangrove and river areas, that are being destroyed and polluted with increasing area utilization and management, including construction of dams and barrages.
Most species are only occasionally caught in gillnets . In the areas where these species live, there are widespread, uncontrolled artisanal fisheries. The river sharks are caught for local consumption, but also for international trade.

It could be, that we will lose these species before we have even gotten to know them. And that is unfortunately not a first….

Sources:
http://www.elasmo-research.org/conservation/river_sharks.htm
Sharks of the World: https://www.facebook.com/SharksoftheWorld
IUCN Red List: www.iucnredlist.org

Some river sharks were caught and brought to a Melbourne aquarium for research purposes. You can watch a video of river sharks here:

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