The freshwater sawfish (Pristis pristis) was recently listed as the most Evolutionarily Distinct and Globally Endangered (EDGE) animal. The Fitzroy River in the remote Kimberley region of north-western Australia represents a significant stronghold for the species, which uses the freshwater reaches of the river as a nursery. There is also mounting pressure to develop the water resources of the region for agriculture that may substantially affect life history dynamics of sawfish in this system. However, the relationship between hydrology and population dynamics of freshwater sawfish was unknown. We used standardized catch data collected over 17 years to determine how wet season volume influences recruitment of freshwater sawfish into their riverine nursery. Negligible recruitment occurred in years with few days of high flood levels (above 98th percentile of cease-to-flow stage height), and relatively high recruitment occurred in years with 14 or more days of high flood levels. This relationship is indicative of a distinct boom-or-bust cycle, whereby freshwater sawfish rely almost entirely on the few years with large wet season floods, and the brief periods of highest water levels within these years, to replenish juvenile populations in the Fitzroy River nursery. This has direct implications for sustainable water resource management for the Fitzroy River basin in order to preserve one of the last known intact nursery habitats for this globally threatened species.
Bibliographical noteFunding Information:
We acknowledge substantial support and field assistance from the Nyikina-Mangala Rangers over a long period, as well as support from the Bunuba Rangers, Kimberley Land Council, Yiriman Project, Dambimangari Rangers, Mary Island Fishing Club, Jarlmadangah Community, Yeeda Station, Liveringa Station, Looma Community, Mitre 10 Derby, Willare Roadhouse, people of Derby, Fitzroy Crossing and Broome, as well numerous field volunteers, including M. Aitken, L. Fraser Buckle, L. Marshall, J. Watson, M. Marshall, B. Marshall, R. Watson, C. Watson, K. Watson, N. Watson, J. Albert, D. Giles, H. Wallace-Smith, J. Mansfield, D. Keynes, M. Allen, J. Keleher, E. Byrnes, S. Visser, J. Duncan, C. Morgan, R. Morgan, N. Morgan, J. Wade, A. Rowland, H. Gill, Z. Hogan, T. Campbell, H. Ashe, G. Teasdale, E. Dobinson, B. Norman, T. Ryan and many others. We also gratefully acknowledge support for our Kimberley base by J. and G. Kelly. The project was variably funded by many organizations over a long period for which we are greatly appreciative, including: Murdoch University, Chevron Wheatstone Project, Australian Federal Government (Australian Research Council, Natural Heritage Trust, Land & Water Australia, Department of Environment, Water, Heritage and the Arts), Western Australian Government State Natural Resource Management Program, Forrest Research Foundation, Holsworth Wildlife Research Fund, Worldwide Fund for Nature, National Geographic, Herman Slade Foundation, Animal Planet and Aquarium Society of New South Wales. K.O.L. was supported by an Australian Government Research Training Program Scholarship and the Forrest Research Foundation.
© 2019, The Author(s).