River sharks are among the rarest and most endangered sharks in the world, and two of the rarest were recently rediscovered in Papua New Guinea by a research team late last year. In a report published on PLOS ONE earlier this month, an international team of scientists documented the discovery of both speartooth sharks and New Guinea River sharks in the Western Province of Papua New Guinea. It is the first time that either of the species have been seen in the country since the late 1960s and early 1970s.

“The fact that adult [speartooth sharks], a large apex predator, have thus far gone unnoticed highlights the rarity of river sharks which combined with their occurrence in remote, poorly-surveyed regions, have resulted in Glyphis species being some of the least known sharks,” researchers stated in the published study.

Only six known species of sharks are capable of living in freshwater: the bull shark and five species of river sharks. Of the latter, the speartooth shark is perhaps the most famous. The large predator makes its home in the tropical waters of northern Australia and New Guinea, feasting on freshwater fish and preferring dark environments. On average they grow up to six feet. Despite their large size, they are not considered a danger to humans due to their extreme rarity. Experts believe there are less than 2,500 mature individuals of this species in the entire world, and no more than 200 in any one local population.

The New Guinea river shark, which is generally slightly larger, is even more rare. Fewer than 250 mature individuals are believed to exist. This species is perhaps best known for being caught by extreme angler Jeremy Wade during the filming of an episode of River Monsters. When Wade realized how rare the fish he just caught was, the animal was immediately released.

You can watch that video below:

Conservationists say that while the focus is on large, more popular sharks such as the great white, protecting more obscure species remains difficult. With more and more research on these rare river sharks, scientists hope they can contribute to direct conservation efforts that will keep them from going extinct.

“In the last decade or so, increased research on the two species which occur in northern Australia has drastically improved our knowledge on this group of sharks and will allow for more directed management plans to be developed,” Will White, the study’s lead author, told The Washington Post.

Image from Twitter

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  • There is one more shark species which has been recorded in freshwater. This is the Pondicherry Shark (Carcharhinus hemiodon) which has been recorded in the Menik River in south Sri Lanka. This makes seven species capable of living in freshwater.