The largest of the sawfishes is the Critically Endangered green sawfish Pristis zijsron, a species believed to have undergone a major decline (38%) in extent of occurrence. Conservation efforts are hampered by the lack of information on the habitat requirements of this species. We used passive acoustic telemetry to document the movement patterns of 37 juvenile P. zijsron ( < 3000 mm total length) in a recently discovered nursery area in a remote estuary and adjacent mangrove creeks in the Pilbara region of Western Australia. All age classes had a high site fidelity near the mouth of the Ashburton River ( < 700 m upstream) or in the adjacent tidal mangrove creeks. Neonates stayed close to the river mouth for several months, with movement in creasing with growth. For larger individuals, movement between the river mouth or creeks and nearshore coastal habitats was largely tidally driven, with nearshore coastal habitats used during low tide and protected tidal waters (mangrove creeks) used during high tide. Emigration from the river estuary appeared to be influenced by increases in freshwater discharge and high turbidity brought on by cyclonic rainfall events. The high relative abundance and site fidelity of multiple age classes of P. zijsron over multiple years confirms that the study area provides important nursery habitats for the species. Additionally, the localised movements of juveniles suggest that this population may be sensitive to disturbances within these habitats. Given the significance of this region for P. zijsron, it is imperative to focus conservation efforts here to ensure that the population remains in a relatively healthy condition.
Bibliographical noteFunding Information:
Acknowledgements. We thank the people of Onslow that assisted with the project, particularly Geoff Herbert and Andrew Slater (Scubaroo Dive). Thanks also to Mat Fraser and Travis Hurley (URS Australia) and Glen Young, Tony Rouphael, Ceri Morgan, Steve Moore, Joe Sanderson and Neil Page (Chevron Australia Pty Ltd) for help with logistics. This project was funded by Chevron Australia Pty Ltd and administered through the Western Australian Science Institution. The study adhered to the conditions of the Murdoch University Animal Ethics Committee and the Department of Fisheries, Government of Western Australia. We acknowledge the input of the referees who greatly assisted with structuring of the manuscript.
© The authors 2017.