Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences

Ontogenetic depth partitioning by juvenile freshwater sawfish (Pristis microdon: Pristidae) in a riverine environment

Jeff M. Whitty A , David L. Morgan A C , Stirling C. Peverell B , Dean C. Thorburn A and Stephen J. Beatty A

A Centre for Fish and Fisheries Research, Murdoch University, Murdoch, WA 6150, Australia.

B Department of Primary Industries and Fisheries, Sustainable Fisheries, Northern Fisheries Centre, Cairns, Qld 4870, Australia.

C Corresponding author. Email:

Marine and Freshwater Research 60(4) 306-316
Submitted: 30 May 2008  Accepted: 29 December 2008   Published: 29 April 2009


The freshwater sawfish (Pristis microdon) is a critically endangered elasmobranch. Ontogenetic changes in the habitat use of juvenile P. microdon were studied using acoustic tracking in the Fitzroy River, Western Australia. Habitat partitioning was significant between 0+ (2007 year class) and larger 1+ (2006 year class) P. microdon. Smaller 0+ fish generally occupied shallower water (<0.6 m) compared with 1+ individuals, which mainly occurred in depths >0.6 m. Significant differences in hourly depth use were also revealed. The depth that 1+ P. microdon occupied was significantly influenced by lunar phase with these animals utilising a shallower and narrower depth range during the full moon compared with the new moon. This was not observed in 0+ individuals. Habitat partitioning was likely to be related to predator avoidance, foraging behaviours, and temperature and/or light regimes. The occurrence of 1+ P. microdon in deeper water may also result from a need for greater depths in which to manoeuvre. The present study demonstrates the utility of acoustic telemetry in monitoring P. microdon in a riverine environment. These results demonstrate the need to consider the habitat requirements of different P. microdon cohorts in the strategic planning of natural resources and will aid in the development of management strategies for this species.

Additional keywords: external tagging, ontogeny, telemetry.


We would like to thank the Department of the Environment, Water, Heritage and the Arts (DEWHA) for financially supporting the project. Thanks in particular to Narelle Montgomery (DEWHA) for project support. We would also like to thank the Jarlmadangah Rangers (Travis Fazeldean, Kimberley Watson, Nyaburu Watson, Kenny Watson, Angus Butt, Josh Albert and William Lennard), the Yiriman Project (Hugh Wallace-Smith, Michelle Coles, Darryl Combs, Mick Apanah and Simon Keenan), Mark Allen, Simon Visser, Nicole Phillips, Ferdy Bergmann and Ryan Bell for their assistance in the field. Thanks to Alan Lymbery and James Tweedley for statistical assistance. Thanks to Yeeda Station and Liveringa Station for access on their land and Mitre 10 Derby for donating consumables to the project. We would like to thank Jim and Gerry Kelly for allowing us to store equipment and ourselves at their residence. Finally, we would like to thank the reviewers of this document, including Colin Simpfendorfer, for their aid in increasing the value of this work. This research was made possible by an exemption from the Fish Resources Management Act 1994 that was provided by the Western Australia Department of Fisheries (Permit no. 190-2008-40). Ethics approval for this work was provided by Murdoch University’s Ethics Board.


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