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Quarterly Report – Q4 2021

Key performance summary

Dashboard description:

This interactive display provides an overview of progress by the Crown-of-Thorns Starfish (COTS) Control Program and the broader reconnaissance program since the Control Program’s expansion and implementation of the integrated pest management (IPM) approach to COTS management in November 2018. It also tracks financial year-to-date metrics and year-on-year comparisons of Coral Cover and COTS numbers.

The program aims to protect coral from COTS predation by culling starfish to maintain numbers below ecologically sustainable levels (i.e. below density levels where coral growth and recovery can outpace COTS predation) on high-value reefs in the Marine Park.

This dashboard highlights where these ‘target’ reefs are located, why they have been selected for management, and what management action has taken place. Financial year-to-date achievements from the fourth quarter of 2021 (October-December 2021) are also highlighted. These achievements build upon the progress reported to date.

  • Management action categories:
  • Culled, currently, unsustainable – reefs where COTS culling occurred during the reporting period, but COTS numbers remain unsustainable. Target threshold not achieved. Culling will continue in the next period.
  • Culled, sustainable levels achieved – reefs where COTS culling has occurred during the reporting period, and COTS were culled to a sustainable level. Target threshold achieved. Monitoring will continue in the next period.
  • Culled, sustainable levels not achievable – reefs where COTS culling was conducted during the period, but numbers were too high to be effectively managed. Some targeted culling may occur at these reefs to reduce COTS larval supply.
  • Monitored, remains sustainable –reefs where COTS were monitored during the period and have remained below sustainable threshold levels. Monitoring will continue in the next period.
  • Reconnaissance, COTS detected – reefs where COTS were detected at the target reef during the period. Culling will commence once resources are available.
  • Requires surveillance – reefs where surveillance is required to determine the management course of action.

Interactivity:

Click on a segment of either ’Management region’ or ‘Management Action’ to filter information on the page. Use “CTRL + Click” to filter for both a Management Area and Management Action. Status’ CTRL + click the reset button in the bottom left corner to reset all filters.

Program to date (November 2018 – December 2021)

  • 268 high-value reefs distributed throughout the Great Barrier Reef Marine Park (GBRMP) have been actioned for COTS management (surveillance and culling) since November 2018. Of these:
    • 141 reefs have been strategically targeted for their high ecological value, including their capacity to spread coral larvae and support the recovery of surrounding reefs following impacts such as coral bleaching and tropical cyclones.
    • 47 have been targeted due to their high economic value and support for significant tourism operations.
    • 80 have been targeted because they have both high ecological and high economic value.
  • A larger number of reefs have been managed in the Far Northern and Northern regions than in the Central and Southern regions. High numbers of COTS on many reefs in the Central and Southern regions have required intensive cull efforts over extended periods to effectively manage COTS and protect coral.

 

  • Since November 2018:
    • 13,090 hectares of reef have been surveyed using manta tow to search for signs of COTS activity and to assess coral status and trends.
    • Wherever COTS and/or their feeding scars were detected, dive teams were deployed to conduct thorough searches and cull starfish.
    • Dive teams spent 42,763 hours searching for and culling 319,753 COTS.
    • Coral loss due to COTS predation has been reduced on 17,120 hectares of the reef (1,712 cull sites).
    • COTS numbers have been reduced to sustainable levels for coral at 86% of the cull sites actioned for COTS management.

Quarter 4 (1 October - 31 December) 2021

  • Eighty-six (86) high-value reefs were actioned between October and December 2021.
    • Manta tow surveillance covered 1,082 hectares of the reef, searching for signs of COTS activity and assessing coral status.
    • Dive teams spent 3,918 dive hours searching for and culling 18,115 COTS.
    • Coral loss due to COTS predation was reduced on 5,610 hectares of the reef (561 cull sites).
    • COTS numbers were successfully reduced to sustainable levels for coral at 79% of the cull sites actioned in the reporting period.
  • Of the 86 reefs actioned for COTS management in Q4 (Oct-Dec) 2021:
  • Cull operations are currently ongoing at 38 reefs (44.2%). Culling will continue on these reefs until sustainable COTS density thresholds are achieved.
  • COTS were culled, and numbers were reduced to sustainable levels on 31 reefs (36%). Monitoring will continue in the next reporting period.
  • Cull operations conducted on 1 reef (1.2%) revealed that COTS numbers were too high to be effectively reduced to sustainable levels with currently available resources. Cull operations were suspended at this reef.
  • Surveillance monitoring was conducted at 14 reefs (16.3%), and COTS numbers were below levels that are sustainable for coral growth and recovery. Monitoring will continue in the next reporting period.
  • COTS were detected on 1 reef (1.2%), and culling operations will commence when resources become available.
  • Opportunistic surveillance was conducted at an additional 1 (1.2%) non-target priority reef which is adjacent to a target reef. No COTS or feeding scars were detected at this reef.

Tracking ‘Outbreak status’ on COTS Control Program target reefs

Dashboard description:

This interactive display shows the location of individual high-value target reefs managed by the COTS Control Program. The map panel on the left shows the outbreak status of target reefs during the 2020/21 financial year.

Reefs that were not actioned in 2020/21 are displayed as grey ‘No Data’ dots. The map panel on the right shows the most recent (2021/22) record of outbreak status for each of the target reefs. The summary figures in the bottom right of the maps are filtered to only include reefs that have data for both years to make year-on-year comparisons more accurate.

‘Outbreak status’ is determined based on the average number of COTS recorded during manta tow surveys around the perimeter of target reefs. Tracking outbreak status changes through time indicate the progress achieved by the COTS Control Program in the effective management of starfish populations.

Reefs classified as ‘No COTS Detected’ (dark green dots) recorded no COTS or COTS feeding scars during manta tow surveillance. Reefs classified as ‘No Outbreak’ status (bright green dots) recorded an average of between 0 to 0.1 COTS per manta tow (2,000 m2 survey area). ‘Potential Outbreak’ reefs (yellow dots) recorded an average of 0.1 to 0.22 COTS per tow. ‘Established Outbreak’ reefs (orange dots) recorded an average of 0.22 to 1 COTS per tow. ‘Severe Outbreak’ reefs (red dots) recorded an average of greater than 1 COTS per tow.

It is important to note that COTS often aggregate for both feeding and spawning, resulting in large variability in COTS density estimates among individual manta tow surveys. Although average COTS numbers are low on ‘No Outbreak’ reefs, there may be specific sites on these reefs where COTS numbers are above sustainable levels, and targeted culling is required to protect coral.

Interactivity:

Select a management area on the left to filter maps and donut charts, zoom in to specific reefs, and hover over a point to reveal additional summary information. CTRL + click the reset button in the bottom left corner to reset all filters. Click a map to hide the doughnut chart and inspect reef level information. Click outside of the map to make the doughnut chart reappear. From the ‘Repeat Surveillance’ box, select “yes” to see which reefs have had repeat surveillance. From the ‘2021/22’ box select “yes” to only see target reefs for this year.

Regional breakdown of COTS Control Program progress

  • Between October and December 2021, the COTS management effort focused on 86 high-value target reefs across the Marine Park's Northern, Central and Southern regions.
    • COTS management in the Northern region is essential because this is the region of the Marine Park where COTS outbreaks first emerge.
    • COTS management in the Central and Southern regions of the Marine Park is important because reefs currently support high coral cover and have the highest COTS.

Far North

  • No reefs were managed by Control Program vessels during this reporting period. Additionally, there are no Far Northern reefs on the 2021/22 Target list due to logistical challenges and lower COTS activity in the region.
  • Reconnaissance and monitoring surveys were conducted by the Reef Joint Field Management Program (RJFMP) and the Australian Institute of Marine Science (AIMS). As a result, low COTS were detected at several reefs, and these findings will inform the operational deployment of Control Program vessels in 2022-23.

Northern Region

  • 42 reefs in the Northern region were managed during this reporting period to maintain low COTS densities and suppress the potential development of a new primary outbreak.
  • 25 reefs were surveyed in both 2020/21 and 2021/22. Across these reefs, the proportion of manta tows with COTS scarring increased from 6.7% to 10.5%, and the average number of COTS per tow increased from 0.007 - 0.008. This is well below the “No Outbreak” threshold of 0.11 COTS/tow.
  • During Q4 2021/22 (of the 42 actioned reefs):
    • 17 reefs transitioned from ‘No Data’ to ‘No COTS Detected’ status (7 reefs) and ‘No Outbreak’ status (10 reefs).
    • 13 reefs remained at ‘No Outbreak’ Status.
    • 2 reefs (Arlington and Ribbon No 4) transitioned from ‘No Outbreak’ to ‘No COTS Detected’ status.
    • 5 reefs remained at ‘No COTS Detected’ status.
    • 4 reefs transitioned from ‘No COTS Detected’ to ‘No Outbreak’ status.
  • 1 reef (Normanby-Mabel) transitioned from ‘Potential Outbreak’ to ‘No Outbreak’ status.

Central Region

  • Twenty-six reefs in the Central region were managed during this reporting period to suppress COTS outbreaks and protect live coral.
  • Across 16 reefs surveyed in both 2020/21 and 2021/22, the proportion of manta tows with COTS scarring increased slightly from 19.2% to 20.0%, while the average COTS per tow decreased from 0.054 to 0.027. Again, this is below the “No Outbreak” threshold of 0.11 COTS/tow.
  • During Q4 2021/22 (of the 26 actioned reefs):
    • Nine reefs remained at ‘No Outbreak’ status.
    • One reef (Pith) transitioned from ‘No Outbreak’ to ‘No COTS Detected’ status.
    • One reef (Davies) transitioned from ‘No Outbreak’ to ‘Potential Outbreak’ status.
    • One reef (Wheeler) transitioned from ‘Potential Outbreak’ to ‘No Outbreak’ status.
    • One reef (Big Broadhurst No. 1) transitioned from ‘Established Outbreak’ to ‘No Outbreak’.
    • One reef (Davies) has increased from ‘No Outbreak’ to ‘Potential Outbreak’ status.
    • Two reefs (Hayman Island and Langford-Bird) recorded ‘No COTS Detected’ status in 2020/21. Although COTS were detected during this reporting period and targeted culling was conducted at these reefs, manta tow was not viable due to low water clarity (visibility), and Outbreak status could not be calculated. In addition, ten reefs were not surveyed in 2020/21:
      • Finally, six fringing reefs at Hook Island in the Whitsunday Islands group recorded ‘No Data’. Although COTS were detected and targeted culling was conducted at these reefs, manta tow was not viable due to low water clarity (visibility), and Outbreak status could not be calculated.
      • Three reefs (Yamacutta, Lodestone and Darley) recorded ‘No Outbreak’ status.
      • One reef (Roxburgh) recorded a ‘No COTS Detected’ status.

Southern Region

  • 18 reefs in the Southern region were managed during this reporting period to suppress COTS outbreaks and protect live coral.
  • Across 17 reefs surveyed in both 2020/21 and 2021/22, the proportion of manta tows with COTS scarring decreased from 21.2% to 12.2%, while the average number of COTS recorded per tow declined from 0.721 (Established Outbreak) to 0.082 (No Outbreak).
  • During Q4 2021/22 (of the 18 actioned reefs):
    • 9 reefs remained at ‘No Outbreak’ status.
    • 2 reefs (Polmaise and Erskine) remained at ‘No COTS Detected’ status.
    • 1 reef (U/N 22-088-a) remained at ‘Severe Outbreak’ status.
    • 1 reef (Fitzroy) remained at ‘Established Outbreak’ status.
    • 1 reef (Obstruction) transitioned from ‘Severe Outbreak’ to ‘Established Outbreak’ status.
    • 1 reef (Mast Head) transitioned from ‘No COTS Detected’ to ‘No Outbreak’ status.
    • 1 reef (Hoskyn Island) transitioned from ‘No Outbreak’ to ‘Established Outbreak’ status.
    • 1 reef (Llewellyn) transitioned from ‘No Outbreak’ to ‘No COTS Detected’ status.
    • 1 reef (Sykes) recorded ‘Potential Outbreak’ status and was not surveyed in 2020/21.

Tracking ‘Coral Cover’ on COTS Control Program target reefs

Dashboard description:

This interactive display shows the location of individual high-value target reefs managed by the COTS Control Program. The map panel on the left shows the coral cover status of target reefs during the 2020/21 financial year.

Reefs that were not actioned in 2020/21 are displayed as grey ‘No Data’ dots. The map panel on the right shows the most recent (2021/22) record of coral cover status for each of the target reefs.  The summary figures in the bottom right of the maps are filtered to only include reefs that have data for both years to make year-on-year comparisons more accurate.

‘Coral cover status’ is determined based on the average coral cover recorded during manta tow surveys around the perimeter of target reefs. Tracking changes in coral cover status through time indicates the coral protection outcomes achieved by the COTS Control Program and helps quantify other cumulative impacts on reef health.

Interactivity:

Select a management area on the left to filter maps and donut charts, zoom in to specific reefs, and hover over a point to reveal additional summary information. CTRL + click the reset button in the bottom left corner to reset all filters.
Click a map to hide the doughnut chart and inspect reef level information. Click outside of the map to make the doughnut chart reappear. From the ‘Repeat Surveillance’ box, select “yes” to see which reefs have had repeat surveillance. From the ‘2021/22’ box select “yes” to only see target reefs for this year.

Regional breakdown of Coral Cover in the COTS Control Program

Far Northern Region

 

  • No reefs were managed by Control Program vessels during this reporting period. There are no Far Northern reefs on the 2021/22 Target list due to logistical challenges and lower COTS activity in the region.
  • Reconnaissance and monitoring surveys were conducted by the Reef Joint Field Management Program (RJFMP) and the Australian Institute of Marine Science (AIMS). Coral cover estimates from these surveys will inform operational deployment of Control Program vessels in 2022-23.

Northern Region

  • 42 reefs in the Northern region were managed during this reporting period to maintain low COTS densities and suppress the potential development of a new primary outbreak.
  • Across the 25 reefs surveyed in both 2020/21 and 2021/22, average hard coral cover decreased from 17.9 % (+/- 2.7%) to 11.6% (+/- 1.41%).
  • During Q4 2021/22 (of the 42 actioned reefs)
    • 8 reefs remained in the 0-10% coral cover category.
    • 1 reef (Thetford) increased from the 0-10% to the 11-30% coral cover category
    • 7 reefs remained in the 11-30% coral cover category.
    • 5 reefs decreased from the 11-30% to the 0-10% coral cover category.
    • 1 reef (Fitzroy Island No. 1) remained in the 31-50% coral cover category.
    • 2 reefs (Eyrie and Agincourt) decreased from 31-50% to the 11-30% coral cover category.
    • 1 reef (U/N 16-013b) decreased from 51-75% to the 11-30% coral cover category.
    • 17 reefs were not surveyed in 2020/21. Nine (9) of these reefs recorded 11-30% coral cover and 8 reefs recorded 0-10% coral cover.

Central Region

  • 26 reefs in the Central region were managed during this reporting period to supress COTS outbreaks and protect live coral.
  • On 16 reefs surveyed in both 2020/21 and 2021/22, average hard coral cover decreased from 18.7 % (+/- 3.33%) to 13.6% (+/- 1.48%).
  • During Q4 2021/22 (of the 26 actioned reefs):
    • 4 reefs remained in the 0-10% coral cover category.
    • 1 reef (Big Broadhurst No1) increased from the 0-10% to the 11-30% coral cover category.
    • 7 reefs remained in the 11-30% coral cover category.
    • 4 reefs decreased from 31-50% to 11-30% coral cover category.
    • 10 reefs were not surveyed in 2020/21:6 fringing reefs at Hook Island in the Whitsunday Island group recorded ‘No Data’. Manta tow surveys were not viable at these reefs due to low water clarity (visibility) and coral cover status could not be calculated.
    • 3 reefs (Yamacutta, Roxburgh and Darley) recorded coral cover of 11-30% and 1 reef (Lodestone) recorded coral cover of 0-10%.

Southern Region

  • 18 reefs in the Southern region were managed during this reporting period to supress COTS outbreaks and protect live coral.
  • On 17reefs surveyed in both 2020/21 and 2021/22, average hard coral cover decreased from 36.7% (+/- 4.29%) to 30.7% (+/- 3.21%).
  • During Q4 2021/22 (of the 18 actioned reefs):
    • 1 reef (Polmaise) remained in the 0-10% coral cover category.
    • 4 reefs remained in the 11-30% coral cover category.
    • 1 reef (Obstruction) decreased from the 11-30% to the 0-10% coral cover category.
    • 1 reef (Pike) increased from the 11-30% to the 31-50% coral cover category.
    • 5 reefs remained in the 31-50% coral cover category.
    • 1 reef (Erskine) decreased from the 31-50% to the 11-30% coral cover category.
    • 1 reef (Lady Elliot Island) remained in the 51-75% coral cover category.
    • 2 reefs (Llewellyn and U/N 21-544) decreased from the 51-75% to the 31-50% coral cover category.
    • 1 reef (Hoskyn Islands) decreased from the 51-75% to the 11-30% coral cover category.

Case Study: Batt Reef

Dashboard description:

The interactive display provides an overview of progress in COTS management at Batt Reef in the Northern region of the Marine Park. The map in the top panel shows where COTS were detected during initial manta tow surveillance conducted prior to culling (January 2019).

The map on the bottom panel shows outcomes from the most recent surveillance (October 2021). Pink dots on these maps indicate the locations where COTS were seen, white dots indicate where COTS scars were detected, and blue dots indicate locations where no COTS were detected.

Catch-per-unit effort (CPUE) defines the number of COTS culled per minute, and it is tracked over time to assess progress in achieving COTS numbers that are sustainable for coral growth and recovery. The graph on the top right panel shows the trend in CPUE for each COTS size class over repeated visits to conduct culling at Batt Reef. The dotted blue line on the graph is the target CPUE threshold below which coral can be sustained.

The bottom right panel provides a summary of the total COTS surveillance and cull effort invested at Batt Reef since November 2018 and during the current reporting period (October-December 2021).

Interactivity:

Hover over dots on the maps to see number of COTS observed, COTS scars and hard coral cover estimates. Zoom out (scroll) to see the location of Batt Reef.

COTS Control at Batt Reef

Batt Reef is in the Northern Great Barrier Reef offshore from Port Douglas. This reef provides an example of the importance of repeated surveillance to detect emerging COTS outbreaks and targeted culling to suppress them to sustainable levels.

COTS numbers were initially low at Batt Reef, with minor amounts of culling required in January and August/September 2019 as well as in February 2020 to maintain sustainable COTS densities. In October 2021, significant levels of scarring and larger COTS were detected, and culling was reinitiated.

What was the initial situation?

  • Initial manta tow surveillance conducted in January 2019 revealed a low-level COTS population with minimal scarring (No Outbreak: 0.00 COTS/Manta Tow).
  • Initial Reef Health Impact Surveys (RHIS) estimated 21-25% hard coral cover, which is sufficient to sustain a severe COTS outbreak.
  • Based on this estimate of hard coral cover, a CPUE threshold of 0.04 COTS culled per minute was established as the ecologically sustainable threshold for coral growth and recovery.
  • Cull operations were conducted at Batt Reef during 4 visits between January 2019 and February 2020. At the conclusion of the February 2020 visit, target CPUE thresholds had been achieved at all opened cull sites and the reef was transitioned to maintenance mode.
  • Repeat surveillance was conducted in August 2020, no COTS or scarring was detected and the reef remained in maintenance mode.
  • Subsequent surveillance in October 2021 detected significant COTS activity and intensive culling operations were reinstated over 8 visits between October and December 2021.
  • From October to December 2021, 622 diver hours were spent searching for and culling 2,823 COTS. Reef-level CPUE was reduced from a peak of 0.17 to 0.06 COTS culled per minute.
  • Cull operations will be maintained at Batt Reef until COTS numbers are reduced to below the sustainable coral growth and recovery threshold at all cull sites.

 

What did the program do?

How is the situation now?

  • Repeat surveillance from these reefs is due to be conducted in January/February 2022. It is expected that reduced COTS numbers and relatively stable coral cover will be recorded.
  • Intensive culling operations remain underway on 16 of the 47 cull sites which have been actioned to date.

Data Sharing

To access any of the observation data collected by the Control Program please send your data request to cotsprogram@gbrmpa.gov.au.

Previous quarterly reports

The COTS Control Program collects large volumes of data that are used to target and maximise the efficacy and efficiency of the Program. The Authority analyses and summarises Reef-wide COTS and coral health data and applies rigorous data quality assurance (QA) and quality control (QC) processes.

To aid interpretation, ‘Quarterly dashboard reports’ are prepared that include the assignment of a ‘management mode’ category to each of the target reefs that were actioned during the reporting period.

Quarterly reports are released as soon as each quarter’s voyage data has been collated, analysed and checked. Because our QA and QC processes are continuous, in a small number of cases previously reported Program statistics may need to be updated. Updates are provided alongside the relevant reports.

Q1 2021 quarterly report update:
In this reporting period, the decision has been made to include non-target Priority Reefs in our reporting. These are reefs that have been identified as a “priority” for COTS Control (600 Reefs), but were not included in the “target-reef” list for this year. Occasionally, due to weather or other logistical constraints, priority reefs may be opportunistically surveyed by control program vessels to assess COTS and coral status.

An additional 15 priority reefs that were monitored by the control program since November 2018 have been included in the Q2, 2021 report that were not included in previous reports, and thus some program to date numbers were higher than previously reported:

  • Reefs actioned – Original figure 224; Corrected figure 239
  • Km of reef surveyed – Original figure 10,542 km; Corrected figure 10,698 km

Additionally, the decision has been made to exclude culling data from 4 voyages conducted in November 2018 before the Integrated Pest Management framework was introduced, and thus Program to date culling figures are lower than previously reported:

  • Ha of reef controlled – Original figure 12,580; Corrected figure 12,340
  • Culling hours – Original figure 32,834; Corrected figure 32,243
  • COTS Culled – Original figure 254,703; Corrected figure 250,734

Quarterly Report – Q1 2021

Crown-of-thorns starfish Control Program:

Dashboard description: This interactive display provides an overview of progress by the Crown-of-Thorns Starfish (COTS) Control Program since its expansion and the application of a new approach to COTS management in November 2018.

The goal of the Program is to protect coral from COTS predation by culling starfish to maintain numbers below ecologically sustainable levels (i.e. below density levels where coral growth and recovery can outpace COTS predation). This will assist coral growth to outpace the impact of COTS on high-value reefs in the Marine Park. This dashboard highlights where these ‘target’ reefs are located, why they have been selected for management, and what management action has taken place. Achievements from the first quarter of 2021 (January-March 2021) are also highlighted. These achievements build upon the progress reported to date.

Management actions:

  • Culled, currently unsustainable - During this period COTS were culled but remain unsustainable, culling will continue in next period.
  • Culled, sustainable levels achieved - During this period COTS were culled to a sustainable level, threshold achieved. Monitoring will continue in next period.
  • Monitored, remains sustainable - During this period COTS were monitored and have remained sustainable, threshold maintained. Monitoring will continue in next period.
  • Reconnaissance, COTS Detected – During this period COTS were detected by reconnaissance surveys. Culling operations will commence when resources become available.

Interactivity: Click on a segment of either "Management Area" or "Management Action" to filter information on the page. Use “CTRL + Click” to filter for both a Management Area and Management Action. CTRL + click the reset button in the bottom left corner to reset all filters.

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Program to date (November 2018 – March 2021)

 

  • 224 high value ‘target’ reefs have been actioned by the COTS Control Program since November 2018. Of these:
    • 115 reefs have been strategically targeted for COTS management due to their high ecological value, including their capacity to spread coral larvae and support the recovery of surrounding reefs following impacts such as coral bleaching and tropical cyclones.
    • 42 have been targeted due to their high economic value, as they support significant tourism operations.
    • 67 have been targeted because they have both high ecological and high economic value.
  • Target reefs are distributed throughout all regions of the Marine Park,
  • More reefs have been managed in the Far Northern and Northern regions compared to the Central and Southern regions. This is because high numbers of COTS on many reefs in the Central and Southern regions mean that more time and effort is required at each reef to effectively manage COTS and protect coral.
  • Since November 2018:
    • 10,542 kilometres of reef has been manta towed to search for signs of COTS activity.
    • Wherever COTS and / or their feeding scars were detected, dive teams were deployed to conduct thorough searches and cull starfish.
    • Dive teams spent 32,834 hours searching for and culling 254,703 COTS.
    • Coral predation by COTS has been reduced on 12,580 hectares of reef.

Quarter 1 (1 January – 31 March) 2021

 

  • COTS management actions were conducted at 45 high value ‘target’ reefs between January and March 2021.
    • 666 kilometres of reef was manta towed to search for signs of COTS activity.
    • Dive teams spent 3,704 dive hours searching for and culling COTS.
    • 25,088 COTS were culled across 2,900 hectares of reef.
  • Of the 45 actioned reefs in Q1 (Jan – Mar) 2021:
    • Surveillance monitoring (where COTS numbers are below levels that are sustainable for coral growth and recovery) was conducted at 5 reefs (11.1%). Monitoring will continue in the next reporting period.
    • COTS were culled and numbers were reduced to sustainable levels on 10 reefs (22.2%). Monitoring will continue in the next reporting period.
    • Cull operations were ongoing on 29 reefs (64.4%). Culling will continue on these reefs until sustainable COTS thresholds are achieved.
    • COTS were detected on one additional reef (2.2%) and culling operations will commence when resources become available.

Tracking ‘Outbreak status’ on COTS Control Program target reefs

Dashboard description: This interactive display shows the location of individual high value target reefs managed by the COTS Control Program. The map panel on the left shows the ‘Outbreak status’ of target reefs prior to the initiation of COTS management. The map panel on the right shows the most recent record of ‘Outbreak status’ for each of the target reefs.

‘Outbreak status’ is determined based on the average number of COTS recorded during manta tow surveys of target reefs. Tracking changes in ‘Outbreak status’ through time provides an indication of the progress achieved by the COTS Control Program.

Reefs classified as “No COTS Detected” (i.e. dark green dots) recorded no COTS or COTS feeding scars during surveillance. Reefs classified as ‘No Outbreak’ status (i.e. bright green dots) support COTS numbers that are below the thresholds that are sustainable for coral growth and recovery. It is important to note that this does not mean that the reefs are completely free of COTS. A reef may be assigned ‘No Outbreak’ status following a period of intensive management action to reduce COTS numbers to sustainable levels, or due to findings from proactive monitoring surveys that focus on detection of COTS outbreaks and informing the distribution of cull effort to efficiently reduce COTS numbers and protect coral.

Interactivity: Select a management area on the left to filter maps and donut charts or zoom in to specific reefs and hover over a point to reveal additional summary information. CTRL + click the reset button in the bottom left corner to reset all filters. Click a map to hide the doughnut chart and inspect reef level information. Click outside of the map to make doughnut chart reappear. Maps are filtered to show reefs managed this quarter by default, toggle the “Managed this Period” button to show all of the reefs managed by the program to date.

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Regional breakdown of COTS control progress

  • Between January and March 2021, COTS management effort focused on 45 high value target reefs across the Northern, Central and Southern regions of the Marine Park.
  • COTS management in the Northern region is important because this is a key region of the Marine Park where COTS outbreaks first emerge.
  • COTS management in the Central and Southern regions of the Marine Park is important because reefs in these regions currently support high coral cover and have the highest numbers of COTS.

Far North

  • No reefs were managed during this reporting period because previous surveillance showed very few or no COTS in this region.

North

  • 14 reefs in the Northern region were managed during this reporting period in order to maintain low COTS densities and suppress the development of a potential subsequent outbreak. Since the commencement of COTS management:
    • 8 reefs have transitioned from ‘No COTS Detected’ to ‘No Outbreak’ status
    • 3 reefs have maintained ‘No Outbreak’ status
    • 1 reef (Eddy Reef) has transitioned from ‘No Outbreak’ to ‘No COTS Detected’
    • 1 reef (Sudbury No 1) has maintained ‘No COTS Detected’ status
    • 1 reef (Normanby-Mabel) has increased from ‘No COTS Detected’ to ‘Potential Outbreak’. Culling is currently underway at this reef to control the emerging outbreak.

 

Central

10 reefs in the Central region were managed during this reporting period. Since the commencement of COTS management:
2 reefs (John Brewer Reef and Keeper Reef) have transitioned from ‘Severe Outbreak’ to ‘No Outbreak’ status
2 reefs (Trunk Reef and Big Broadhurst Reef) have transitioned from ‘Established Outbreak’ (Trunk Reef) and ‘Potential Outbreak’ (Big Broadhurst Reef) to ‘No Outbreak’ status
1 reef (Britomart Reef) transitioned from ‘Established Outbreak’ to ‘No COTS Detected’
5 reefs were maintained at ‘No Outbreak’ status

South

 

  • 21 reefs in the Southern region were managed during this reporting period. Since the commencement of COTS management:
    • 5 reefs have been maintained at ‘No Outbreak’ status.
    • 5 reefs have been maintained at ‘No COTS Detected’ status.
    • 2 reefs (Fitzroy Reef and Lady Musgrave Reef) have transitioned from ‘Established Outbreak’ to ‘No Outbreak’ status.
    • 2 reefs (Llewellyn Reef and Boult Reef) have transitioned from ‘Potential Outbreak’ to ‘No Outbreak’ (Llewellyn Reef) and ‘No COTS Detected’ (Boult Reef) status.
    • 3 reefs (Mast Head, Hoskyn Islands and Erskine) transitioned from ‘No Outbreak’ to ‘No COTS Detected’ status.
    • 3 reefs (Obstruction, U/N 21-557, U/N 22-084) increased from either ‘No Outbreak (Obstruction), ‘Potential Outbreak’ (U/N 21-557) or ‘Established Outbreak’ (U/N 22-084) to ‘Severe Outbreak’. This was due to the limited resources available for culling in the Swains during the preceding year. Cull efforts are ongoing to reduce these populations to levels sustainable for coral growth and recovery.
    • 1 reef (Wilson Reef) maintained ‘Severe Outbreak’ status. 

 

 

Case Study: Eddy Reef

Dashboard description: The interactive display provides an overview of progress in COTS management at Eddy Reef. The map in the top panel shows the results from manta tow surveillance before the pest management process began, and the map on the bottom panel shows outcomes from the latest surveillance. Red dots on these maps indicate the locations where COTS were detected. Green dots indicate locations where no COTS were detected.

Catch-per-unit effort (CPUE) defines the number of COTS culled per minute and it is tracked over time to assess progress in achieving COTS numbers that are sustainable for coral recovery, maintenance and growth. The graph on the top right panel shows the trend in CPUE for each COTS size class over repeated visits to conduct culling at Eddy Reef. The dotted blue line on the graph is the target CPUE below which coral can be sustained.

The bottom right panel provides a summary of total COTS surveillance and cull effort invested at Eddy reef since November 2018, and during the current reporting period (January-March 2021).

Interactivity: Hover over dots on the maps to see number of COTS observed, COTS scars and hard coral cover estimates. Zoom out (scroll) to see the location of Eddy Reef.

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COTS Control at Eddy Reef
  • Eddy Reef is in the Northern Great Barrier Reef offshore from Tully. Eddy Reef provides an example of the importance of continued surveillance of reefs even after COTS populations have been successfully culled to below target thresholds. If signs of COTS are observed again, intensive culling recommences until COTS numbers are again reduced to below the thresholds that are sustainable for coral growth and recovery.

What was the initial situation?

  • Initial manta tow surveillance in November 2018 revealed that Eddy Reef had a low-level COTS population (No Outbreak: 0.01 COTS/Manta Tow), with aggregations of COTS primarily on the southern aspect of the reef.
  • Initial Reef Health Impact Surveys (RHIS) estimated 10-14% hard coral cover at this reef.
  • Based on this estimate of hard coral cover, a CPUE threshold of 0.04 COTS culled per minute was established as the ecologically sustainable threshold for coral growth and recovery.

What did the program do?

 

  • Eddy reef was intensively culled during 13 repeat visits between November 2018 and April 2019. The reef-level CPUE was reduced from a peak of 0.10 to 0.00 COTS culled per minute.
  • Repeated manta tow surveillance indicated that cull operations had successfully reduced COTS densities and achieved ‘No Outbreak’ status.
  • In July 2020, repeat surveillance identified COTS scarring and 10 COTS were culled at a CPUE of 0.02, meaning the reef remained in maintenance mode.
  • In October 2020, repeat surveillance identified increased COTS activity and intensive cull operations were reinstated.Since October 2020, Control program divers spent a total of 321 hours searching for and culling 1,562 COTS over the course of 6 visits.
  • Since November 2018, 1,410 diver hours have been invested in searching for and culling 6,206 COTS during 20 visits.

How is the situation now?

  • No COTS were detected on the most recent surveillance voyage (March 2021), and target thresholds have been achieved at all sites
  • Repeat surveillance of Eddy Reef will be conducted within 6 months to ensure COTS numbers remain below sustainable thresholds.
  • Recent surveys have estimated that Coral Cover has increased from 10-14% to 15-19%.
Previous quarterly reports

The COTS Control Program collects large volumes of data that are used to target and maximise the efficacy and efficiency of the Program. The Authority analyses and summarises Reef-wide COTS and coral health data and applies rigorous data quality assurance (QA) and quality control (QC) processes.

To aid interpretation, ‘Quarterly dashboard reports’ are prepared that include the assignment of a ‘management mode’ category to each of the target reefs that were actioned during the reporting period. Quarterly reports are released as soon as each quarter’s voyage data has been collated, analysed and checked. Because our QA and QC processes are continuous, in a small number of cases previously reported Program statistics may need to be updated. Updates are provided alongside the relevant reports. Links to previous reports may be found below this text.

 

Quarterly Report – Q2 2021

Crown-of-thorns starfish Control Program:

Key performance summary

Dashboard description: This interactive display provides an overview of progress by the Crown-of-Thorns Starfish (COTS) Control Program since its expansion and implementation of an integrated pest management (IPM) approach to COTS management in November 2018.

The goal of the Program is to protect coral from COTS predation by culling starfish to maintain numbers below ecologically sustainable levels (i.e. below density levels where coral growth and recovery can outpace COTS predation). This will assist coral growth to outpace the impact of COTS on high-value reefs in the Marine Park. This dashboard highlights where these ‘target’ reefs are located, why they have been selected for management, and what management action has taken place. Achievements from the second quarter of 2021 (April-June 2021) are also highlighted. These achievements build upon the progress reported to date.

Management action categories:

  • Culled, currently unsustainable - reefs where COTS culling has occurred during the reporting period but COTS numbers remain at unsustainable levels, and culling will continue in the next period.
  • Culled, sustainable levels achieved - reefs where COTS culling has occurred during the reporting period and COTS were culled to a sustainable level. Target threshold achieved. Monitoring will continue in the next period.
  • Monitored, remains sustainable - reefs where COTS were monitored during the period and have remained below sustainable threshold levels. Monitoring will continue in the next period.
  • Reconnaissance, COTS Detected – reefs where COTS were detected at the target reef during the period. Culling will commence once resources are available.

Interactivity: Click on a segment of either "Management Area" or "Management Action" to filter information on the page. Use “CTRL + Click” to filter for both a Management Area and Management Action. CTRL + click the reset button in the bottom left corner to reset all filters.

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Program to date (November 2018 – June 2021)

  • 253 high value reefs distributed throughout the Great Barrier Reef Marine Park have been actioned for COTS management (surveillance and culling) since November 2018. Of these:
    • 130 reefs have been strategically targeted for COTS management due to their high ecological value, including their capacity to spread coral larvae and support the recovery of surrounding reefs following impacts such as coral bleaching and tropical cyclones.
    • 43 have been targeted due to their high economic value, as they support significant tourism operations.
    • 80 have been targeted because they have both high ecological and high economic value.
  • A larger number of reefs have been managed in the Far Northern and Northern regions than in the Central and Southern regions. This is because high numbers of COTS on many reefs in the Central and Southern regions requires that more time and effort is invested at each reef to effectively manage COTS and protect coral.
  • Since November 2018:
    • 11,342 hectares of reef has been surveyed using manta tow to search for signs of COTS activity and to assess coral status and trends.
    • Wherever COTS and / or their feeding scars were detected, dive teams were deployed to conduct thorough searches and cull starfish.
    • Dive teams spent 35,667 hours searching for and culling 276,623 COTS.
    • Coral loss due to COTS predation has been reduced on 13,630 hectares of reef.
    • COTS numbers have been reduced to sustainable levels for coral at 83.1% of the cull sites at reefs actioned for COTS management

Quarter 2 (1 April – 30 June) 2021

  • COTS management actions were conducted at 51 high value reefs (48 2020-21 Target Reefs and 3 reefs from the broader list of Priority Reefs) between April and June 2021.
  • Manta tow surveillance covered 644 hectares of reef searching for signs of COTS activity and assessing coral status.
  • Dive teams spent 3,425 dive hours searching for and culling 25,889 COTS.
  • Coral loss due to COTS predation was reduced on 3,290 hectares of reef.
  • COTS numbers were successfully reduced to sustainable levels for coral at 75.4% of the cull sites at actioned reefs.
  • Of the 51 reefs actioned for COTS management in Q2 (Apr – Jun) 2021:
    • Surveillance monitoring (where COTS numbers are below levels that are sustainable for coral growth and recovery) was conducted at 1 reef (2.0%). Monitoring will continue in the next reporting period.
    • COTS were culled and numbers were reduced to sustainable levels on 6 reefs (11.8%). Monitoring will continue in the next reporting period.
    • Cull operations were ongoing on 35 reefs (68.6%). Culling will continue on these reefs until sustainable COTS thresholds are achieved.
    • COTS were detected on 6 reefs (11.8%) and culling operations will commence when resources become available.
    • Opportunistic surveillance was conducted at an additional 3 non-target priority reefs ahead of planned COTS management action in the 2021/22 financial year.
    • Tracking ‘Outbreak status’ on COTS Control Program target reefs.
    • Tracking ‘Outbreak status’ on COTS Control Program target reefs

Dashboard description: This interactive display shows the location of individual high value target reefs managed by the COTS Control Program. The map panel on the left shows the outbreak status of target reefs prior to the initiation of COTS management. The map panel on the right shows the most recent record of outbreak status for each of the target reefs.

‘Outbreak status’ is determined based on the average number of COTS recorded during manta tow surveys around the entire perimeter of target reefs. Tracking changes in outbreak status through time provides an indication of the progress achieved by the COTS Control Program in effective management of starfish populations.

Reefs classified as ‘No COTS Detected’ (dark green dots) recorded no COTS or COTS feeding scars during manta tow surveillance. Reefs classified as ‘No Outbreak’ status (bright green dots) recorded an average of between 0 to 0.1 COTS per manta tow (2,000 m2 survey area). ‘Potential Outbreak’ reefs (yellow dots) recorded an average of 0.1 to 0.22 COTS per tow. ‘Established Outbreak’ reefs (orange dots) recorded an average of 0.22 to 1 COTS per tow. ‘Severe Outbreak’ reefs (red dots) recorded an average of greater than 1 COTS per tow.

It is important to note that COTS often aggregate for both feeding and spawning and this can result in large variability in COTS density estimates among individual manta tow surveys. Although average COTS numbers are low on ‘No Outbreak’ reefs, there may be specific sites on these reefs where COTS numbers are above sustainable levels and targeted culling is required to protect coral.

Interactivity: Select a management area on the left to filter maps and donut charts or zoom in to specific reefs and hover over a point to reveal additional summary information. CTRL + click the reset button in the bottom left corner to reset all filters. Click a map to hide the doughnut chart and inspect reef level information. Click outside of the map to make doughnut chart reappear. Maps are filtered to show reefs managed this quarter by default, toggle the ’Managed this Period‘ button to show all of the reefs managed by the program to date. From the selection box in the top left of the map select “yes” to see which reefs have had repeat surveillance.

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Regional breakdown of COTS Control Program progress

  • Between April and June 2021, COTS management effort focused on 51 high value target reefs across the Northern, Central and Southern regions of the Marine Park.
    • COTS management in the Northern region is important because this is the region of the Marine Park where COTS outbreaks first emerge.
    • COTS management in the Central and Southern regions of the Marine Park is important because reefs in these regions currently support high coral cover and have the highest numbers of COTS.

Far North

  • No reefs were managed during this reporting period because previous surveillance showed very few or no COTS in this region.

North

  • 14 reefs in the Northern region were managed during this reporting period in order to maintain low COTS densities and suppress the development of a potential subsequent outbreak. Since the commencement of COTS management:
    • 6 reefs have transitioned from ‘No COTS Detected’ to ‘No Outbreak’ status
    • 4 reefs have transitioned from ‘No Outbreak’  to ‘No COTS Detected’ status
    • 2 reefs (Briggs and Farquharson) have remained at ‘No Outbreak’ Status
    • 1 reef (Scott Reef) was surveyed for the first time and ‘No COTS Detected’ status was recorded.
    • 1 reef (Normanby-Mabel) has transitioned from ‘No COTS Detected’ to ‘Potential Outbreak’. Culling is currently underway at this reef to control the emerging outbreak.

Central

  • 16 reefs in the Central region were managed during this reporting period. Since the commencement of COTS management:
    • 3 reefs have remained at ‘No Outbreak’ status.
    • 5 reefs were surveyed for the first time and ‘No Outbreak’ status was recorded.
    • 2 reefs (John Brewer and Keeper) have transitioned from ‘Severe Outbreak’ to ‘No Outbreak’ status.
    • 2 reefs (Britomart and Trunk) have transitioned from ‘Established Outbreak’ to ‘Potential Outbreak’ status.
    • 1 reef (Big Broadhurst No 2) was surveyed for the first time and ‘Established Outbreak’ status was recorded.
    • 1 reef (Little Broadhurst) was surveyed for the first time and ‘Potential Outbreak’ status was recorded.
    • 1 reef (Big Broadhurst No 1) has increased from ‘Potential Outbreak’ to ‘Established Outbreak’ status.
    • 1 reef (Wheeler) has increased from ‘No Outbreak’ to ‘Potential Outbreak’ status.

South

  • 21 reefs in the Southern region were managed during this reporting period. Since the commencement of COTS management:
    • 5 reefs have been maintained at ‘No Outbreak’ status.
    • 5 reefs were surveyed for the first time and a ‘No Outbreak’ status was recorded.
    • 2 reefs (Llewellyn and Boult) have transitioned from ‘Potential Outbreak’ to ‘No Outbreak’ status.
    • 1 reef (Fitzroy) has remained at ‘Established Outbreak’ status.
    • 1 reef (Lady Musgrave) has transitioned from ‘Established Outbreak’ to ‘No Outbreak’ status.
    • 3 reefs (Obstruction, U/N 21-557, U/N 22-084) increased from ‘No Outbreak (Obstruction), ‘Potential Outbreak’ (U/N 21-557) or ‘Established Outbreak’ (U/N 22-084) to ‘Severe Outbreak’. This was due to the limited resources available for culling in the Swains during the preceding year. Cull efforts are ongoing to reduce these populations to levels sustainable for coral growth and recovery.
    • 4 reefs were surveyed for the first time and ‘Severe Outbreak’ status was recorded.

Case Study: Normanby-Mabel and Round-Russel Reefs

Dashboard description: The interactive display provides an overview of progress in COTS management at Normanby-Mabel and Round-Russel reefs in the northern region of the Marine Park. The map in the top panel shows where COTS were detected during initial manta tow surveillance conducted prior to culling (February 2020). The map on the bottom panel shows outcomes from the most recent surveillance (January 2021). Red dots on these maps indicate the locations where COTS were detected. Green dots indicate locations where no COTS were detected.

Catch-per-unit effort (CPUE) defines the number of COTS culled per minute and it is tracked over time to assess progress in achieving COTS numbers that are sustainable for coral recovery, maintenance and growth. The graph on the top right panel shows the trend in CPUE for each COTS size class over repeated visits to conduct culling at Normanby-Mabel and Round-Russel reefs. The dotted blue line on the graph is the target CPUE threshold below which coral can be sustained.

The bottom right panel provides a summary of total COTS surveillance and cull effort invested at Normanby-Mabel and Round-Russel reefs since November 2018, and during the current reporting period (April-June 2021).

Interactivity: Hover over dots on the maps to see number of COTS observed, COTS scars and hard coral cover estimates. Zoom out (scroll) to see the location of Normanby-Mabel and Round-Russel reefs.
 

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COTS Control at Normanby-Mabel and Round-Russel reefs

Normanby-Mabel and Round-Russel reefs are in the northern Great Barrier Reef offshore from Innisfail. These reefs provide an example of the importance of sustained culling on reefs in their pre-Outbreak phase. While COTS numbers were initially low at these reefs, two cohorts of younger COTS (0-15 cm juveniles and 15-25 cm sub-adults) have emerged since initial surveillance in February 2020.  Early detection and proactive management of the COTS outbreak at these reefs has restricted the increase in COTS numbers and prevented the rapid loss of coral that would have eventuated if these reefs had reached “Established” or “Severe” outbreak status. There is currently increasing evidence of an emerging primary outbreak on reefs in the Northern region of the Marine Park. The COTS Control Program is providing early detection of emerging COTS outbreaks and effective suppression of COTS numbers to levels that are sustainable for coral growth and recovery.

What was the initial situation?

  • Initial manta tow surveillance in February 2020 revealed a low-level COTS population (No Outbreak: 0.01 COTS/Manta Tow), on Round-Russel reef.
  • Initial Reef Health Impact Surveys (RHIS) estimated 24-37% hard coral cover at this reef, indicating there was sufficient live coral present to sustain a severe COTS outbreak.
  • Based on this estimate of hard coral cover, a CPUE threshold of 0.04 COTS culled per minute was established as the ecologically sustainable threshold for coral growth and recovery.
  • Normanby-Mabel and Round-Russel reefs was intensively culled during 18 repeat visits between August 2020 and June 2021. The reef-level CPUE was reduced from a peak of 0.53 to 0.10 COTS culled per minute across both reefs and a total of 507 diver hours have been invested in searching for and culling 6,463 COTS over the course of 18 visits.
  • Repeated manta tow surveillance in January 2021 indicated that while cull operations had successfully reduced COTS densities and maintained ‘No Outbreak’ status, younger cohorts of COTS were emerging and aggregations were still identified on most sections of both reefs (see map above).
  • Cull operations were initiated in August 2020 to reduce COTS aggregations

What did the program do?

How is the situation now?

  • Repeat surveillance from these reefs is due to be conducted in August 2021, and it is expected that reduced COTS numbers will be recorded.
  • Intensive culling operations remain underway on 8 of 15 cull sites which have been actioned at the two reefs.
  • Recent surveys have estimated that despite the ongoing low-level COTS outbreak, cull operations have maintained coral cover between 25-32%.

Previous quarterly reports

The COTS Control Program collects large volumes of data that are used to target and maximise the efficacy and efficiency of the Program. The Authority analyses and summarises Reef-wide COTS and coral health data and applies rigorous data quality assurance (QA) and quality control (QC) processes.

To aid interpretation, ‘Quarterly dashboard reports’ are prepared that include the assignment of a ‘management mode’ category to each of the target reefs that were actioned during the reporting period. Quarterly reports are released as soon as each quarter’s voyage data has been collated, analysed and checked. Because our QA and QC processes are continuous, in a small number of cases previously reported Program statistics may need to be updated. Updates are provided alongside the relevant reports.

 

Quarterly Report – Q3 2021

Q3 2021 quarterly report update:

Minor database errors have been rectified since the publishing of this report and program to date culling figures are higher than previously reported:

  • Culling hours – Original figure 38,831; Corrected figure 38,845
  • COTS Culled – Original figure 301,597; Corrected figure 301,638

Key performance summary

Dashboard description: This interactive display provides an overview of progress by the Crown-of-Thorns Starfish (COTS) Control Program since the Control Program’s expansion and implementation of an integrated pest management (IPM) approach to COTS management in November 2018.

The goal of the Program is to protect coral from COTS predation on high-value reefs throughout the Marine Park via strategic culling of starfish to maintain numbers below ecologically sustainable levels (i.e. below density levels where coral growth and recovery can outpace COTS predation). This dashboard highlights where these ‘target’ reefs are located, why they have been selected for management, and what management action has taken place since the Reef-wide expansion of the Program 2018. Achievements from the third quarter of 2021 (July-September 2021) are also highlighted and build upon the Program outcomes reported in previous quarterly reports (see links below).

Management action categories:

  • Culled, currently unsustainable - reefs where COTS culling has occurred during the reporting period but COTS numbers remain at unsustainable levels, and culling will continue in the next period.
  • Culled, sustainable levels achieved - reefs where COTS culling has occurred during the reporting period and COTS were culled to a sustainable level. Target threshold achieved. Monitoring will continue in the next period.
  • Culled, sustainable levels not achievable - reefs where COTS culling was conducted during the period, but numbers were too high to be reduced below sustainable thresholds in order to protect coral. Some targeted culling may occur at these reefs in the future as a means to reduce COTS larval supply.
  • Monitored, remains sustainable - reefs where COTS were monitored during the period and have remained below sustainable threshold levels. Monitoring will continue in the next period.
  • Reconnaissance, COTS detected - reefs where COTS were detected at the target reef during the period. Culling will commence once resources are available.
  • Requires surveillance - reefs where surveillance is required to determine the management course of action.

Interactivity: Click on a segment of either ’Management region’ or ‘Management Action’ to filter information on the page. Use “CTRL + Click” to filter for both a Management Area and Management Action. Status’ CTRL + click the reset button in the bottom left corner to reset all filters.

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Program to date (November 2018 – September 2021)

 

  • 255 high value reefs distributed throughout the Great Barrier Reef Marine Park have been actioned for COTS management (surveillance and culling) since November 2018. Of these:
    • 136 reefs have been strategically targeted for COTS management due to their high ecological value, including their capacity to spread coral larvae and support the recovery of surrounding reefs following impacts such as coral bleaching and tropical cyclones.
    • 43 have been targeted due to their high economic value, as they support significant tourism operations.
    • 76 have been targeted because they have both high ecological and high economic value.
  • A larger number of reefs have been managed in the Far Northern and Northern regions than in the Central and Southern regions. High numbers of COTS on many reefs in the Central and Southern regions has meant that more time and effort is required at each reef to effectively suppress COTS and protect coral.
  • Since November 2018:
    • 12,008 hectares of reef has been surveyed using manta tow to search for signs of COTS activity and to assess coral status and trends.
    • Wherever COTS and / or their feeding scars were detected, dive teams were deployed to conduct thorough searches and conduct culling.
    • Dive teams have invested 38,831 hours searching for and culling 301,597 COTS.
    • Coral loss due to COTS predation has been reduced on 14,220 hectares of reef.
    • COTS numbers have been reduced to sustainable levels at 84% of the cull sites at reefs actioned for COTS management.

Quarter 3 (1 July – 30 September) 2021

  • COTS management actions were conducted at 50 Target Reefs between July and September 2021.
    • Manta tow surveillance covered 666 hectares of reef searching for signs of COTS activity and assessing coral status.
    • Dive teams spent 3,167 dive hours searching for and culling 24,982 COTS.
    • Coral loss due to COTS predation was reduced on 2,820 hectares of reef.
    • COTS numbers were successfully reduced to sustainable levels for coral at 82% of the cull sites at actioned reefs.
  • Of the 50 reefs actioned for COTS management in Q3 (Jul – Sep) 2021:
    • Cull operations are currently ongoing at 30 reefs (60.0%). Culling will continue on these reefs until sustainable COTS density thresholds are achieved.
    • COTS were culled and numbers were reduced to sustainable levels on 7 reefs (14.0%). Monitoring will continue in the next reporting period.
    • Cull operations conducted on 4 reefs (8.0%) revealed that COTS numbers were too high to be effectively reduced to sustainable levels with currently available resources. Cull operations were ceased at these reefs.
    • Surveillance monitoring (where COTS numbers are below levels that are sustainable for coral growth and recovery) was conducted at 5 reefs (10.0%). Monitoring will continue in the next reporting period.
    • COTS were detected on 2 reefs (4.0%) and culling operations will commence when resources become available.
    • Incomplete surveillance was conducted at 1 reef (2.0%), surveillance will be completed in the next reporting period.
    • Opportunistic surveillance was conducted at an additional 1 (2.0%) non-target priority reef which is adjacent to a target reef.

Tracking ‘Outbreak status’ on COTS Control Program target reefs

Dashboard description: This interactive display shows the location of individual high value target reefs managed by the COTS Control Program. The map panel on the left shows the outbreak status of target reefs during the 2020/21 financial year. Reefs that were not actioned in 2020/21 are displayed as grey ‘No Data’ dots. The map panel on the right shows the most recent (2021/22) record of outbreak status for each of the target reefs. The summary figures in the bottom right of the maps are filtered to only include reefs that have data for both years to make year on year comparisons more accurate.

‘Outbreak status’ is determined based on the average number of COTS recorded during manta tow surveys around the entire perimeter of target reefs. Tracking changes in outbreak status through time provides an indication of the progress achieved by the COTS Control Program in effective management of starfish populations.

Reefs classified as ‘No COTS Detected’ (dark green dots) recorded no COTS or COTS feeding scars during manta tow surveillance. Reefs classified as ‘No Outbreak’ status (bright green dots) recorded an average of between 0 to 0.1 COTS per manta tow (2,000 m2 survey area). ‘Potential Outbreak’ reefs (yellow dots) recorded an average of 0.1 to 0.22 COTS per tow. ‘Established Outbreak’ reefs (orange dots) recorded an average of 0.22 to 1 COTS per tow. ‘Severe Outbreak’ reefs (red dots) recorded an average of greater than 1 COTS per tow.

It is important to note that COTS often aggregate for both feeding and spawning and this can result in large variability in COTS density estimates among individual manta tow surveys. Although average COTS numbers are low on ‘No Outbreak’ reefs, there may be specific sites on these reefs where COTS numbers are above sustainable levels and targeted culling is required to protect coral.

Interactivity: Select a management area on the left to filter maps and donut charts or zoom in to specific reefs and hover over a point to reveal additional summary information. CTRL + click the reset button in the bottom left corner to reset all filters. Click a map to hide the doughnut chart and inspect reef level information. Click outside of the map to make doughnut chart reappear. From the ‘Repeat Surveillance’ box select “yes” to see which reefs have had repeat surveillance. From the ‘2021/22’ box select “yes” to only see target reefs for this year.

Regional breakdown of COTS Control Program progress

  • Between July and September 2021, COTS management effort focused on 50 high value reefs across the northern, central and southern regions of the Marine Park.
    • COTS management in the northern region is important because this is the region of the Marine Park where COTS outbreaks first emerge.
    • COTS management in the Central and Southern regions of the Marine Park is important because reefs in these regions currently support high coral cover and have the highest numbers of adult COTS.

Far Norther Region

  • No reefs were managed during this reporting period because previous surveillance showed very few or no COTS in this region.

Northern Region

  • 22 reefs in the Northern region were managed during this reporting period in order to maintain low COTS densities and suppress the development of a potential subsequent outbreak.
  • On reefs surveyed in both 2020/21 and 2021/22, the proportion of manta tows with COTS scarring has dropped slightly from 12.0% to 11.3%, while the average number of COTS recorded per tow has remained stable at 0.004, well below the “No Outbreak” threshold of 0.11 COTS/tow.
  • During 2021/22:
    • 6 reefs have transitioned from ‘No Outbreak’  to ‘No COTS Detected’ status
    • 6 reefs have remained at ‘No Outbreak’ Status
    • 3 reefs (Michaelmas, Hastings and Batt) have transitioned from ‘No COTS Detected’ to ‘No Outbreak’ status
    • 2 reefs (Vlassoff and Norman) have remained at ‘No COTS Detected’ Status
    • 3 reefs (Beaver, Rudder and U/N 16-027)  recorded ‘No COTS Detected’ status and were not surveyed in 2020/21
    • 2 reefs (Tongue and Green Island Reef)  recorded ‘No Outbreak’ status and were not surveyed in 2020/21

Central Region

  • 12 reefs in the Central region were managed during this reporting period in order to reduce COTS densities protect the high levels of coral cover in the region.
  • On reefs surveyed in both 2020/21 and 2021/22, the proportion of manta tows with COTS scarring has increased slightly from 25.5% to 27.6%, while the average number of COTS recorded per tow has declined from 0.12 (Potential Outbreak) to 0.06 (No Outbreak).
  • During 2021/22:
    • 6 reefs have remained at ‘No Outbreak’ status.
    • 2 reefs (Yamacutta and Lodestone) recorded ‘No Outbreak’ status. These reefs were not surveyed in 2020.
    • 1 reef (Big Broadhurst No 2) has transitioned from ‘Established Outbreak’ to ‘Potential Outbreak’.
    • 1 reef (Wheeler) has transitioned from ‘Potential Outbreak’ to ‘No Outbreak’.
    • 1 reef (Big Broadhurst No 1) has transitioned from ‘Established Outbreak’ to ‘No Outbreak’.
    • 1 reef (Davies) has increased from ‘No Outbreak’ to ‘Potential Outbreak’ status.

Southern Region

 

  • 16 reefs in the Southern region were managed during this reporting period in order to reduce COTS densities protect the high levels of coral cover in the region.
  • On reefs surveyed in both 2020/21 and 2021/22, the proportion of manta tows with COTS scarring has decreased slightly from 41.5% to 36.9%, while the average number of COTS recorded per tow has declined from 3.631 (Severe Outbreak) to 1.978 (Severe Outbreak).
  • During 2021/22:
    • 7 reefs have been maintained at ‘No Outbreak’ status.
    • 4 reefs has remained at ‘Severe Outbreak’ status
    • 1 reef (Fitzroy) has remained at ‘Established Outbreak’ status.
    • 1 reef (U/N 22-084) has transitioned from ‘Severe Outbreak’ to ‘Established Outbreak’ status.
    • 1 reef (One Tree Island) has increased from ‘No COTS Detected’ to ‘No Outbreak’ status.
    • 1 reef (Lamont) has increased from ‘No Outbreak’ to ‘Established Outbreak’ status.
    • 1 reef (Wistari) has transitioned from ‘No Outbreak’ to ‘No COTS Detected’ status.
    • 3 of the above reefs (22-084, 22-085, and Wilson) had COTS outbreaks that were too severe to effectively supress to sustainable levels and cull operations have been suspended.

Tracking ‘Coral Cover’ on COTS Control Program target reefs

Dashboard description: This interactive display shows the location of individual high value target reefs managed by the COTS Control Program. The map panel on the left shows the coral cover status of target reefs during the 2020/21 financial year. Reefs that were not actioned in 2020/21 are displayed as grey ‘No Data’ dots. The map panel on the right shows the most recent (2021/22) record of coral cover status for each of the target reefs.  The summary figures in the bottom right of the maps are filtered to only include reefs that have data for both years to make year on year comparisons more accurate.

‘Coral cover status’ is determined based on the average coral cover recorded during manta tow surveys around the entire perimeter of target reefs. Tracking changes in coral cover status through time provides an indication of the progress achieved by the COTS Control Program in effective management of starfish populations.

Interactivity: Select a management area on the left to filter maps and donut charts or zoom in to specific reefs and hover over a point to reveal additional summary information. CTRL + click the reset button in the bottom left corner to reset all filters. Click a map to hide the doughnut chart and inspect reef level information. Click outside of the map to make doughnut chart reappear. From the ‘Repeat Surveillance’ box select “yes” to see which reefs have had repeat surveillance. From the ‘2021/22’ box select “yes” to only see target reefs for this year.

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Regional breakdown of Coral Cover in the COTS Control Program

Far Northern Region

  • No reefs were managed during this reporting period because previous surveillance showed very few or no COTS in this region.

Northern Region

  • 21 reefs in the Northern region were managed during this reporting period in order to maintain low COTS densities and suppress the development of a potential subsequent outbreak.
  • On reefs surveyed in both 2020 and 2021, average hard coral cover decreased slightly from 13.7 % (+/- 2.2%) to 12.0% (+/- 2.2%).
  • During 2021:
    • 5 reefs have remained in the 0-10% coral cover category.
    • 4 reefs have remained in the 11-30% coral cover category.
    • 5 reefs have decreased from the 11-30% to the 0-10% coral cover category.
    • 4 reefs recorded coral cover of 0-10% and were not surveyed in 2020.
    • 2 reefs increased from the 0-10% to 11-30% coral cover category.
    • 1 reef (Fitzroy Island (No 1) remained in the 31-50% coral cover category.
    • 1 reef (Green Island) recorded coral cover of 11-30% and was not surveyed in 2020.

Central Region

  • 12 reefs in the Central region were managed during this reporting period in order to reduce COTS densities protect the high levels of coral cover in the region.
  • On reefs surveyed in both years, average hard coral cover decreased slightly from 18.7 % (+/- 4.4%) to 16.3% (+/- 1.9%).
  • During 2021:
    • 5 reefs have remained in the 11-30% coral cover category.
    • 2 reefs (Big Broadhurst No1 and No2) increased from the 0-10% to the 11-30% coral cover category.
    • 2 reefs (Wheeler and Davies) decreased from the 31-50% to the 11-30% coral cover category.
    • 2 reefs (Yamacutta and Lodestone) recorded coral cover of 0-10% and were not surveyed in 2020.
    • 1 reef (Britomart) remained in the 0-10% coral cover category.

Southern Region

 

  • 16 reefs in the Southern region were managed during this reporting period in order to reduce COTS densities protect the high levels of coral cover in the region.
  • On reefs surveyed in both years, average hard coral cover decreased slightly from 33.6 % (+/- 4.6%) to 27.2% (+/- 3.9%)
  • During 2021:
    • 5 reefs have remained in the 11-30% coral cover category.
    • 3 reefs (Heron, Boult and Fairfax)have remained in the 11-30% coral cover category.
    • 2 reefs (Obstruction and 21-557) decreased from the 11-30% to the 0-10% coral cover category.
    • 2 reefs (One Tree Island and Lady Elliot Island) decreased from the 51-75% to the 31-50% coral cover category.
    • 1 reef (Pike) increased from the 11-30% to the 31-50% coral cover category.
    • 1 reef (Lamont) decreased from the 31-50% to the 11-30% coral cover category.
    • 1 reef (Hoskyn Islands) remained in the 51-75% coral cover category.
    • 1 reef (22-084) remained in the 0-10% coral cover category.

Case Study: Wheeler Reef

Dashboard description: The interactive display provides an overview of progress in COTS management at Wheeler reef in the central region of the Marine Park. The map in the top panel shows where COTS were detected during initial manta tow surveillance conducted prior to culling (August 2019). The map on the bottom panel shows outcomes from the most recent surveillance (July 2021). Pink dots on these maps indicate the locations where COTS were seen, white dots indicate where COTS scars were detected and blue dots indicate locations where no COTS were detected.

Catch-per-unit effort (CPUE) defines the number of COTS culled per minute and it is tracked over time to assess progress in achieving COTS numbers that are sustainable for coral recovery, maintenance and growth. The graph on the top right panel shows the trend in CPUE for each COTS size class over repeated visits to conduct culling at Wheeler reef. The dotted blue line on the graph is the target CPUE threshold below which coral can be sustained.

The bottom right panel provides a summary of total COTS surveillance and cull effort invested at Wheler reef since November 2018, and during the current reporting period (July-September 2021).

Interactivity: Hover over dots on the maps to see number of COTS observed, COTS scars and hard coral cover estimates. Zoom out (scroll) to see the location of Wheeler Reef 

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COTS Control at Wheeler reefs

Wheeler reef is in the Central Great Barrier Reef offshore from Townsville. These reefs provide an example of the importance of repeated surveillance on reefs to detect emerging COTS outbreaks. COTS numbers were initially low at Wheeler Reef with minor amounts of culling required in September 2019 and April 2020 to maintain COTS densities below the threshold for coral growth and recovery. In July 2021 significant levels of scarring and larger COTS were observed.

What was the initial situation?

  • Initial manta tow surveillance in September 2019 and April 2020 revealed a low-level COTS population with some scarring (No Outbreak: 0.00 COTS/Manta Tow), on Wheeler Reef
  • Initial Reef Health Impact Surveys (RHIS) estimated 33-42% hard coral cover at this reef, indicating there was sufficient live coral present to sustain a severe COTS outbreak.
  • Based on this estimate of hard coral cover, a CPUE threshold of 0.04 COTS culled per minute was established as the ecologically sustainable threshold for coral growth and recovery.

What did the program do?

  • Initially, culling was conducted at Wheeler Reef on 3 visits between September 2019 and April 2020
  • After more significant COTS activity was identified in May 2021, intensive culling operations began with an additional 7 visits between May and September 2021 during which reef-level CPUE was reduced from a peak of 0.36 to 0.15 COTS culled per minute.
  • Overall, Wheeler reef has been intensively culled during 10 visits and a total of 369 diver hours have been invested in searching for and culling 3,241 COTS.

How is the situation now?

  • Repeat surveillance from these reefs is due to be conducted in October/November 2021, and it is expected that reduced COTS numbers and relatively stable coral cover will be recorded.
  • Intensive culling operations remain underway on 3 of the 8 cull sites which have been actioned.

Data Sharing

To access any of the observation data collected by the Control Program please send your data request to cotsprogram@gbrmpa.gov.au.

Previous quarterly reports

The COTS Control Program collects large volumes of data that are used to target and maximise the efficacy and efficiency of the Program. The Authority analyses and summarises Reef-wide COTS and coral health data and applies rigorous data quality assurance (QA) and quality control (QC) processes.

To aid interpretation, ‘Quarterly dashboard reports’ are prepared that include the assignment of a ‘management mode’ category to each of the target reefs that were actioned during the reporting period. Quarterly reports are released as soon as each quarter’s voyage data has been collated, analysed and checked. Because our QA and QC processes are continuous, in a small number of cases previously reported Program statistics may need to be updated. Updates are provided alongside the relevant reports.
 

Created Mon, 2022-08-22 10:59
Updated 22 Aug 2022
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