Rare and endangered shark found populating the Roper River

A shark that can grow to be over 2.5 metres in length and is one of only a handful of sharks around the world that occur in rivers has been found in a Top End waterway.

The Speartooth Shark (Glyphis glyphis) is critically endangered and a population has been discovered in the Roper River. Picture: File

An incredibly rare species of river shark, known to inhabit tropical rivers and adjacent waters in northern Australia and Papua New Guinea, has been found populating the Top End’s Roper River.

Researchers from Charles Darwin University and First Nations Yugul Mangi Rangers discovered the critically endangered Speartooth Shark species after a recent surveying of the waterway.

CDU’s Research Institute for the Environment and Livelihoods senior researcher Dr Peter Kyne said the discovery of the population was important for the endangered species long term survival.

“The results of our survey showed that the Speartooth Shark occurs in a limited stretch of the downstream Roper River, and the population could decline rapidly in the face of threats, so we need to determine how these environmental changes impact them and come up with ways of managing them,” he said.

“If we don’t, then this unique and isolated population that calls the Roper River home could be lost forever.”

Charles Darwin University (CDU) researchers and Yugul Mangi Rangers have discovered a population of the rare threatened Speartooth Shark in the Roper River. Picture: Supplied

CDU PhD candidate Julia Constance, who is studying the movement ecology of the Speartooth Shark, said this was an exciting discovery to learn more about the rare species.

“The Speartooth Shark is quite elusive and occurs in very particular habitats. This can make them susceptible to changes in their environment,” she said.

“We do know that female adults return to the same rivers they were born to pup, and that juveniles spend their early years in rivers, so it makes understanding their river habitats all the more important.”

The river sharks can grow to up to 2.5 metres in length and they favour brackish and very muddy waters of large tidal rivers.

The researchers used technical science, as well as a tried and tested fishing technique, to discover the population according to Ms Constance.

“We mapped areas of the river for salinity levels that might point us to where the sharks could be before casting fishing lines in the river,” she said.

“We caught 40 Speartooth Sharks including pups, showing that this is a breeding population.

“We were able to measure each shark, record their sex, assess their level of maturity, and take a genetic sample before releasing them.”

Speartooth Shark (Glyphis glyphis) is critically endangered and a population has been discovered in the Roper River. Picture: File

The research was conducted with the help of the Yugul Mangi Rangers who helped with “fishing compliance” and “identifying any environmental changes” as well as sharing their knowledge of the river.

Yugul Mangi Ranger Davin Hall said the discovery of the population was exciting for his team and the area.

“That’s good we found the Speartooth Shark in the Roper River because we didn’t know they lived in the muddy and brackish water here before,” he said.

• The bullet point summary was created with the assistance of AI technology (PaLM2) then edited and approved for publication by an editor.