We’re combing the rivers of northern Australia to learn more about the size and status of shark populations.

The challenge

Understanding our northern river shark populations

Northern Australia is home to several iconic species of river sharks. Many of these sharks grow slowly, mature late and produce few young, but we don’t know enough about them to assess whether populations are stable, declining or increasing.

Our response

Using acoustic tags to learn more about sharks

We’re working with the National Environmental Research Progam Marine Biodiversity Hub on a three-year project to tag largetooth sawfish, (Pristis pristis) speartooth sharks (Glyphis glyphis) and northern river sharks (Glyphis garricki) in the Top End and Queensland.

The research, which began in 2013, is seeking information about the species’ life history and populations to guide decisions about conservation, wildlife trade regulation and management.

Scientists are combing the rivers, billabongs, and muddy pools of nine major river systems: setting gillnets in likely habitat and watching well into the night to ensure that any captured animals do not remain in the nets too long, or be eaten by crocodiles.

The results

Northern river shark has expanded its range

Internal acoustic tags have been fitted to more than 165 individuals to provide information on movement and migrations, habitat use and survivorship.

Few largetooth sawfish have been caught, indicating they are incredibly uncommon.

Modifications to freshwater river flows, increased crocodile numbers, and variation in rainfall between years, were thought to be potential factors dampening their recovery.

Conversely, the research has revealed an expanded range for the northern river shark, which has been found in a lot more rivers in the area between Darwin and the eastern boundary of Kakadu National Park than was previously thought.

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