Crown-of-thorns starfish (COTS) are voracious coral predators that are native to the Great Barrier Reef. Coral reefs can sustain low numbers of COTS; however, periodic population outbreaks are responsible for widespread loss of coral and degradation of reef habitats. Coral loss from COTS predation compounds upon the cumulative impacts of coral bleaching events, tropical cyclones and other stressors.
The Crown-of-thorns Starfish Control Program is led by the Reef Authority in collaboration with Program partners, contractors and research agencies. The objective of the Program is to protect coral across a network of high-value reefs via targeted surveillance and manual culling of COTS outbreaks.
Control effort is systematically deployed to efficiently and effectively suppress COTS numbers to sustainable levels at which coral growth and recovery can outpace coral predation.
The Program is informed by the best available science and field intelligence to detect, target and suppress starfish outbreaks and maximise coral protection outcomes.
Tracking progress
This 2023-24 Annual Report Dashboard provides an overview of COTS Control Program operations and delivery outcomes, COTS outbreak and coral cover status across all reefs actioned by the Program between 01/07/2023 and 30/06/2024.
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
2023-24 Annual report
- During 2023-24, the Crown-of-thorns Starfish Control Program:
- Actioned 192 target reefs for surveillance and COTS culling where required
- Conducted 30,596 manta tow surveys and 3,524 Reef Health and Impact Surveys (RHIS)
- Culled 50,227 COTS across 11,640 hectares of reef habitat
- Spent 16,657 hours underwater culling
- About the Annual Report:
- This year's reporting includes reefs surveyed and monitored by the Australian Institute of Marine Science Long Term Monitoring Program (AIMS LTMP) and the Reef Joint Field Management Program (RJFMP). Reef survey data generated by LTMP and RJFMP are used to inform COTS Control Program strategic planning, tactical deployment of vessels, and to assess Program outcomes.
- Summary data presented in this report extend from 2012 to present and span the most recent (4th) wave of crown-of-thorns outbreaks on the Great Barrier Reef.
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 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 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 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 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 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 is also displayed.
Previous years reports
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
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.
