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Crown-of-thorns starfish are native coral predators on the Great Barrier Reef. In outbreak proportions, these predators can add additional stress to coral ecosystems. 

The Crown-of-thorns Starfish Control Program, a partnership between the Reef Authority, Great Barrier Reef Foundation and the Reef and Rainforest Research Centre, along with supporting agencies and contractors work to protect corals from outbreaks of these predators. 

Tracking progress

Low numbers of crown-of-thorns starfish are sustainable on coral reefs; however, periodic population outbreaks significantly impact reef health and result in widespread loss of coral. 

The objective of the Crown-of-thorns Starfish Control Program is to protect coral on high-value reefs by suppressing crown-of-thorns starfish numbers to sustainable levels for coral growth and recovery through strategically targeted manual culling. 

Annual data collected by the program is publicly available under Creative Commons license. To access any of the data collected by the Program, please send your data request to cotsprogram@gbrmpa.gov.au  

2022-23 Annual report 

  • During 2022-23, the Crown-of-thorns Starfish Control Program:
  • Actioned 201 target reefs
  • Protected 13,740 hectares of reef habitat through targeted culling
  • Culled 48,225 COTS
  • Spent 21,928 hours underwater
Interactivity: Users can toggle the display to view key performance indicator metrics (panel 1), crown-of-thorns outbreak status (panel 2), live coral cover (panel 3) and culling activity (panel 4). Additionally, selecting a management area from the inset map will filter the display, and finer-scale information is revealed by hovering over a reef of interest. See the descriptions below for details on the calculation of each displayed metric.

  • About the Annual Report:
  • This year's reporting includes reefs monitored by the Australian Institute of Marine Science Long Term Monitoring Program (AIMS LTMP) and the Reef Joint Field Management Program (RJFMP) as survey data from these programs are integrated within the Crown-of-thorns Starfish Control Program and used to inform crown-of-thorns culling activity.
  • Program summary data extends back to 2012, when the control program began work to suppress the most recent wave of crown-of-thorns outbreaks. The Crown-of-thorns Starfish Control Program, however, began in the 2000’s driven primarily by the tourism industry. This data is not included, due to changes to data collection strategies and a focus on the most recent wave of crown-of-thorns outbreaks.


Definitions

  • Management action categories:
  • Culling, crown-of-thorns starfish unsustainable – Actioned reefs where crown-of-thorns starfish culling has occurred, but crown-of-thorns starfish numbers remain above the sustainable level for coral growth and recovery. Culling will continue until the target threshold is achieved.
  • Culling, crown-of-thorns starfish sustainable – Actioned reefs where crown-of-thorns starfish culling has occurred, and crown-of-thorns starfish numbers were reduced to a sustainable level for coral growth and recovery. Monitoring surveys will continue to ensure timely action if crown-of-thorns starfish outbreaks re-emerge. 
  • Culling suspended, unsustainable – Actioned reefs where crown-of-thorns starfish culling was conducted but numbers were too high to be effectively managed. Some targeted culling may occur in future, but resources have currently been diverted from these reefs. Monitoring surveys will continue to track crown-of-thorns starfish outbreak and coral dynamics.
  • Surveyed, remains sustainable – Actioned reefs where crown-of-thorns starfish and coral surveys were conducted, and crown-of-thorns starfish numbers are sustainable for coral growth and recovery. Monitoring surveys will continue to ensure timely action if crown-of-thorns starfish outbreaks re-emerge. 
  • Surveyed, crown-of-thorns starfish detected – Actioned reefs where surveys detected crown-of-thorns starfish outbreaks. Cull operations will commence when resources are available.

Outbreak status is assigned to all actioned reefs. It is calculated as the average number of crown-of-thorns starfish recorded across all manta tow surveys conducted at each reef and it is expressed as crown-of-thorns starfish/tow (2,000 m2 survey area).

Tracking changes in outbreak status through time provides an indication of the progress achieved by the Crown-of-thorns starfish Control Program.

  • Outbreak status classifications are defined as follows:
  • No crown-of-thorns starfish Detected – Manta tow surveys recorded no crown-of-thorns starfish or crown-of-thorns starfish feeding scars.
  • No Outbreak – Manta tow surveys recorded 0 - 0.1 crown-of-thorns starfish/tow. 
  • Potential Outbreak – Manta tow surveys recorded 0.1 - 0.22 crown-of-thorns starfish/tow.
  • Established Outbreak – Manta tow surveys recorded 0.22 - 1 crown-of-thorns starfish/tow.
  • Severe Outbreak – Manta tow surveys recorded > 1 crown-of-thorns starfish/tow.

It is important to note that crown-of-thorns starfish often aggregate for both feeding and spawning and this can result in large variability in crown-of-thorns starfish density estimates among individual manta tow surveys.

Although average crown-of-thorns starfish numbers are low on ‘No Outbreak’ reefs, there may be specific sites on these reefs where crown-of-thorns starfish numbers are above sustainable levels and targeted culling is required to protect coral.

Crown-of-thorns starfish outbreak status values presented in the summary statistics panel are aggregated average estimates for the 2022-23 financial year (Reef-wide and filtered to management area when selected).

Hovering the cursor over individual reefs provides additional information on reef-specific crown-of-thorns starfish outbreak status estimates and most recent manta tow tracks. 

The last survey date for 2022-23 is also displayed. 

  • Live coral cover
  • ‘Percentage categories of live coral cover’ (see bar chart in upper right corner) are the average coral cover estimates generated from manta tow surveys at each actioned reef. Tracking changes in coral cover status through time provides an indication of the coral protection outcomes achieved by the Crown-of-thorns starfish Control Program and helps to quantify other cumulative impacts on reef health.
  • Estimates from Reef Health Impact Surveys (RHIS) are also provided in the summary statistics panel. The Reef Health Impact Survey method usually produces a higher estimate of coral cover than manta tow surveys due to its smaller survey area and focus on shallow reef habitats which tend to support higher coral cover than deeper reef slope habitats surveyed using manta tow.

Live coral cover values presented in the summary statistics panel are aggregated average estimates for the 2022-23 financial year (Reef-wide and filtered to management area when selected). 

Hovering the cursor over individual reefs provides additional information on reef-specific coral cover estimates from both manta tow and Reef Health Impact Survey data. 

The last survey date for 2022-23 is also displayed.

  • ‘Catch per unit effort (CPUE)’ is the total number of crown-of-thorns starfish culled divided by the number of diver minutes spent searching for and culling crown-of-thorns starfish. CPUE is categorized as follows:
  • 0.00 - 0.02 crown-of-thorns starfish/min: crown-of-thorns starfish, while present, have been reduced to densities where coral growth outpaces crown-of-thorns starfish predation. Crown-of-thorns starfish spawning success may be suppressed.
  • 0.02 - 0.04 crown-of-thorns starfish/min: crown-of-thorns starfish have been reduced to densities where coral growth outpaces crown-of-thorns starfish predation on reefs with < 40% live coral cover.
  • 0.04 - 0.08 crown-of-thorns starfish/min: crown-of-thorns starfish have been reduced to densities where coral growth outpaces crown-of-thorns starfish predation on reefs with > 40% live coral cover.
  • 0.08 - 0.2 crown-of-thorns starfish/min: crown-of-thorns starfish are above sustainable densities and coral loss due to crown-of-thorns starfish predation increasingly outpaces coral growth.
  • 0.2 crown-of-thorns starfish/min: crown-of-thorns starfish are well above sustainable densities and rapid coral loss due to crown-of-thorns starfish predation occurs (coral loss to below 5% live cover is expected within 12 months). 

Catch per unit effort values presented in the summary statistics panel are aggregated average estimates for the 2022-23 financial year (Reef-wide and filtered to management area when selected).

Hovering the cursor over individual reefs provides additional information on reef-specific catch per unit effort estimates, total diver hours invested in culling and the total number of crown-of-thorns starfish culled.

The last cull dive date for 2022-23 is also displayed.

Previous years reports

The dashboard below displays key performance indicators and the location and summary information for reefs that were managed by the Crown-of-thorns starfish Control Program during the 2021-22 financial year.

Users can click the ‘select the map view’ buttons to view crown-of-thorns starfish outbreak status, live coral cover and culling activity metrics.

Selecting a management area from the inset map (bottom left corner) will filter the map display and summary statistics to a geographic region.

More detailed (reef-scale) information is revealed by hovering the cursor over a reef of interest.

Created
Updated 23 Apr 2024
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