At least two access ways through freshwater barriers need to be established for endangered freshwater sawfish (Pristis pristis) populations living in the north of Western Australia and other areas need to be monitored according to a new report by Murdoch University researchers.
The report1, funded by the Chevron Wheatstone project through the Western Australian Marine Science Institution (WAMSI) recommended fishways need to be constructed on the Camballin Barrage and the Myroodah Crossing on the Fitzroy River.
|Camballin Barrage, Fitzroy River (Photo: David Morgan)|
Sawfishes are a family of rays with a long, narrow, flattened rostrum, or nose extension, lined with sharp teeth. Some can grow up to seven metres in length. All of Australia’s species of sawfishes are listed as Critically Endangered by the International Union for the Conservation of Nature (IUCN). Research has found their ranges have decreased by 30-80 per cent depending on the species as a result of habitat loss and overfishing2.
|David Morgan holding a tagged Green Sawfish (Photo: Jeff Whitty)|
In northern Western Australia, the Fitzroy river is arguably the most important nursery for freshwater sawfish and the Ashburton River estuary is currently the only identified pupping site and nursery for green sawfish (Pristis zijsron) in the world.
Freshwater Sawfish are born in estuaries before migrating upstream to spend their first four-five years of life in river systems. Locally they have been recorded up to 400 kilometres from the coast in the Fitzroy River. Upon nearing maturity they move back to coastal and marine waters.
|Freshwater sawfish (Photo: David Morgan)|
Dr David Morgan led the research to examine what prevents sawfish in northern Western Australia from being able to migrate.
“The Barrage, on average (2002-2015), reduces the time that Freshwater Sawfish can move upstream by 184 days,” Dr Morgan said.
”Northern Australia represents one of the only remaining population strongholds for this sawfish and although recruitment is linked to river flood, there have been a number of years recently where recruitment has failed.
“The relatively pristine nature of large northern Australian rivers is essential for juvenile freshwater sawfish. We have some understanding of the importance of rivers such as the Fitzroy River in the Kimberley and the Daly River in the Top End. However, we know little about the adult population.
“There is considerable pressure to develop the freshwater resources of northern Australia, but proposals will firmly need to consider impacts on freshwater sawfish.
“Structures such as dams and barrages in rivers are barriers to sawfish migration, while dry season water extraction could reduce available river habitat. Connectivity from estuaries through to upstream reaches of rivers is essential for allowing the species to complete its lifecycle,” Dr Morgan said.
2.Dulvy, N. K., Davidson, L. N. K., Kyne, P. M., Simpfendorfer, C. A., Harrison, L. R., Carlson, J.K., and S. V. Fordham. 2016. Ghosts of the coast: global extinction risk and conservation of sawfishes. Aquatic Conservation: Marine and Freshwater Ecosystems 26:134-153.