Freshwater sawfish in the Fitzroy River are a species under threat from both global warming and a water allocation plan being discussed by the WA Government.
The Fitzroy River catchment in the West Kimberley region of WA occupies an area of 93,829 square kilometres. It is home to four of the five species of sawfish found on earth, all of which are highly vulnerable and are one of the main groups of marine fishes most likely to go extinct.
Three of the sawfish species found in the Fitzroy are solely marine fish, while the critically endangered freshwater sawfish spends its first 4-6 years in freshwater before swimming back to the ocean to mature.
Murdoch University researcher Karissa Lear has spent the last six years studying the sawfish population in the Fitzroy River. She said the river was crucial for the survival of the Freshwater Sawfish species, because it provided a nursery for the juvenile fish.
“The Fitzroy River is now the last known intact nursery habitat for this species in the world, so it’s really important that the Fitzroy sawfish population stays healthy and functioning for the persistence of the species globally,” Dr Lear said.
The two major threats posed to sawfish in the Fitzroy are rising global temperatures and the possible changes to river flow brought about by human development.
Freshwater systems in Australia are one of the key regions predicted to experience a greater increased temperature due to climate change than other parts of the world. Evidence of how global warming will impact the sawfish population can already be observed.
In December of 2018, a mass dying event of sawfish occurred in a small pool within the Fitzroy catchment. The deaths were presumed to be caused by high water temperatures, which were recorded as 37 degrees Celsius at midday.
The Western Australian Government is considering a possible water allocation plan for the Fitzroy River to support economic activity and agricultural industries. The plan is detailed on the website of the Department of Primary Industries and Regional Development.
Evidence collected by Dr Lear and her team suggests even small changes to water levels in the Fitzroy could affect the survival rates of the sawfish population, especially as the effects of these changes accumulate over time.
“Abstracting [or extracting] water would lower the carrying capacity of the river by shrinking habitat and lowering productivity, potentially increasing weight loss in sawfish to the extent that this could lead to mortality during the dry season,” she said.
Nyikina Traditional Owner and former ranger Travis Fazeldean has been working as a research assistant on the Fitzroy project for 16 years. He said the Fitzroy River held immense cultural significance to Aboriginal people in the West Kimberly region: “We have stories that come from the river. We have Aboriginal names for the fish and the animals that are along the river and on the land. The sawfish is actually one of our main perspectives in our stories because it has a vital role in the river through our culture.”
The State Government is bound by the Environmental Protection and Biodiversity Conservation Act to consider the management and protection of any vulnerable species and its habitat, such as that of the freshwater sawfish.
A spokesperson said the Department of Biodiversity, Conservation and Attractions would be “working to create national parks along the Fitzroy River and Margaret River which will provide protection to important sawfish habitat”.
Dr Lear and her team believe the best way to promote sawfish survival is to ensure that any future water allocation plan is conservative and closely monitored.