Sawfish tracking using satellite tag technology

Unfortunately, managers don’t have enough data to understand exactly why population contraction is happening, or how to reverse it.

Among the biggest knowledge gaps is lack of data regarding the movement ecology of mature sawfish that have left coastal nursery areas. Satellite telemetry is the most promising method of collecting this data. This involves the attachment of transmitter ‘tags’ to free-moving animals which send signals to orbiting satellites that track their movements.

Previous experiments with this technique have had mixed success because of technological limitations, and biological characteristics of the sawfishes. Refinement of telemetry tagging techniques to overcome these issues is critical for collection of the sawfish movement data that is necessary for the development of evidence-based conservation strategies and actions that will help protect Australia’s sawfish population.

Approach and findings

Approach

Eight sawfishes of two species were tagged at two intertidal sites in northern Western Australia. Three different tag-types were used: a towed ARGOS PTT; a satellite-linked miniPAT pop-up tag; and, a SPLASH hybrid tag. All were programmed to transmit data, then attached using loop harnesses to the fishes’ dorsal fins.

Findings

Except for two tags that failed to provide viable data (for unknown reasons), all other tags transmitted high-quality location data. This revealed that the tagged sawfishes:

• stayed in shallow sub-tidal and intertidal habitats;
• had high site fidelity, that is, did not move far over the tracking period;
• often moved with tidal lows, probably following foraging opportunities; and
• never swam deeper than eight metres.

Observed species differences were:

• dwarf sawfish, Pristis clavata, were only associated with mangrove-lined creeks; and
• green sawfish, Pristis zijsron, moved widely across their habitat bay’s open intertidal zone and sandflats.

Conclusions

This project has demonstrated that satellite telemetry is an excellent tool for collecting the important data needed to better manage and protect sawfishes. The pilot study also provided valuable learnings on the usefulness of specific tag types and attachment methods that will improve future research outcomes.

We recommend expanded research using satellite tags, throughout areas where sawfish are still common. This will enable the characteristics of critical habitats to be understood and provide the foundation for computer models to predict suitable habitats, elsewhere. This will enable the overlay of location data of present habitat modifications and other threatening processes, to determine where sawfish are most at risk, and therefore areas requiring concerted conservation focus.

Outcomes

• Innovative sawfish monitoring techniques tested and evaluated.
• New data provides information on sawfish ecology to support population conservation.

Project location