Communique 3 May 2023
The Shark Control Program Scientific Working Group (the group) met on 3 May 2023 to review the results of the first phase of the Catch Alert Drumline (CAD) trial.
The Department of Agriculture and Fisheries (the department) provided a presentation on the results of the first phase of the CAD trial. The trial was conducted between 24 January 2022 and 23 January 2023 at 4 beaches on the Capricorn Coast in central Queensland:
- Mulambin Beach
- Tanby Point
- Fisherman's Beach
- Emu Park Beach.
Eleven Catch Alert Drumlines (CADs) were alternated with 11 Modified Traditional Drumlines (MTDs) enabling a comparison of catches and survival of marine fauna caught on the 2 drumline types. Traditional drumlines (TDs) throughout the Shark Control Program use a J-style hook and chain trace. The MTDs used in this trial used the same trace and hook as the CADs (circle hook and wire trace) to ensure results were comparable.
- A total of 99 animals were caught on the 11 MTDs and 66 animals on the 11 CADs during the trial. Three species comprised ~85% of the total catch:
- bull whalers (n=70)
- pigeye whalers (n=51)
- tiger sharks (n=19).
- MTDs caught more target sharks than CADs, however a significant number of these were caught at night, and at dawn and dusk, when CADs were not deployed.
- Catches of target shark species were more likely during the summer months, when sea surface temperatures were highest (>25°C), irrespective of drumline type.
- The 2 most common species caught, bull whalers and pigeye whalers, were mostly small and likely use the turbid waters adjacent to the Fitzroy River for foraging and avoiding predators.
- Survival of bull and pigeye whalers was substantially higher on CADs than MTDs, due to the reduced time the animals spent hooked (mean response time of contractors was 33 minutes), and survival increased with shark size.
- Tiger shark survival was high on both drumline types: however, more data are needed for a robust statistical analysis.
- Overall, CADs increased the survival (at the point of release) of target and non-target species.
- All non-target species caught on CADs (12 animals from 9 species) were released alive.
The group discussed the results and recommended the inclusion of additional analyses comparing trial data (MTDs) with historical catch rates and size distributions (TDs). Group members were invited to provide feedback on the draft report.
The group discussed operational considerations for a trial of CADs at other program locations within the Great Barrier Reef Marine Park:
Based on a site suitability assessment, Cairns was the preferred location for the expanded trial. Townsville and Mackay both presented challenges (e.g. tidal range, prevailing weather and distance covered) that may impact contractors' ability to respond quickly to CAD call outs.
The group, with consideration for available funding, endorsed an extension of the trial on the Capricorn Coast to 2025 and the addition of Cairns as a new trial location. A limited trial at Mackay would also be included to assess the impact of operational constraints identified in the site assessment. The working group also supported a trial of twice daily servicing of TDs at Townsville (weather permitting) where the ability to respond to call outs to CADs during a trial is likely to present significant challenges.
The department committed to continuing to refine the configuration of CADs to reduce the capture of small sharks and to reduce the occurrence of captured animals failing to trigger an alert.