PORT ROPER (Australia)- Charles Darwin University (CDU) researchers and First Nations Yugul Mangi Rangers have discovered a new population of a rare and threatened Speartooth Sharks in the Northern Territory’s Roper River.
The Speartooth Shark or Glyphis glyphis is currently listed as Critically Endangered under Australia’s national environmental legislation, with a very small population and a restricted geographic range. This rare species of river shark inhabits only a small number of tropical rivers and adjacent marine waters in northern Australia and southern Papua New Guinea.
Elusive
CDU PhD candidate Julia Constance, who is studying the movement ecology of the Speartooth Shark, saidthere is still much to learn about this rare species. “The Speartooth Shark is quite elusive and occurs in very particular habitats. This can make them susceptible to changes in their environment. 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 Speartooth Shark 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. They favour brackish and very muddy waters of large tidal rivers. The Roper River, which flows into the remote southwestern Gulf of Carpentaria, contains suitable Speartooth Shark habitat which had not previously been surveyed for the species.
Newborn speartooth sharks
To find out whether a population of Speartooth Sharks lived in the Roper River, researchers travelled to Port Roper in September and November last year. “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,” Ms Constance said.“We caught 40 Speartooth Sharks including pups (newborn sharks), 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,” she said.
The Roper River is a unique environment fed by ground water during the dry season and by runoff from surrounding catchments and rivers such as the Wilton River in the wet season. It is home to iconic barramundi, crocodiles, huge freshwater stingrays, and threatened sawfish.
Knowledge of the river
Ms Constance worked closely with the Yugul Mangi Rangers from Ngukurr who joined the researchers on fieldwork to share knowledge of the river and help the survey efforts. “The rangers will play an important part in helping to protect and preserve these species by helping with recreational fishing compliance and identifying any environmental changes,” Ms Constance said.
Yugul Mangi Ranger Davin Hall said this discovery is exciting for the Rangers. “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,” said Mr Hall.
Read more on the website of the Charles Darwin University
See some footage of a speartooth shark: