Quarterly Report – Q2 2020

Crown-of-thorns starfish Control Program: overview of progress

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

The goal of the program is to protect coral across high value reefs in the Great Barrier Reef Marine Park from crown-of-thorns starfish damage by reducing and maintaining crown-of-thorns starfish numbers at levels where their impact on coral is minimised. This dashboard highlights where these high value reefs are located, why they have been selected for pest management, and what management action has taken place. Achievements from the second quarter of 2020 (April to July 2020) are also highlighted. These achievements build upon the progress from previous months.

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.

Key performance summary

Overarching program:

  • Total number of high value reefs where crown-of-thorns starfish numbers have been managed since November 2018: 185
    • Number of reefs where proactive monitoring has been conducted to ensure crown-of-thorns starfish numbers are below levels that are sustainable for coral: 80 (43.2%)
    • Number of reefs where culling action has been undertaken to reduce crown-of-thorns starfish numbers down to levels that are sustainable for coral: 75 (40.5%)
    • Number of reefs where intensive management is still underway to achieve crown-of-thorns starfish numbers that are sustainable for coral: 30 (16.2%)
    • Percentage of managed reefs where crown-of-thorns starfish numbers are at sustainable levels for coral growth and recovery: 83.7%
  • Of these 185 reefs, 88 have been strategically targeted for pest management because of their high ecological value, including their capacity to spread coral larvae to other reefs which supports recovery from impacts like mass coral bleaching and tropical cyclones.
  • Of these 185 reefs, 34 have been strategically targeted for pest management because of their high economic value, as they support significant tourism operations.
  • Of these 185 reefs, 63 have been targeted because they have both high ecological and economic value.
  • These high value reefs are spread across all regions of the Marine Park, with larger total numbers of reefs managed in the Far Northern and Northern regions, relative to the Central and Southern management regions.
  • This variation across regions is due to the fact that crown-of-thorns starfish numbers are currently much greater on reefs in the Central and Southern regions, which means that it takes more time and effort to effectively manage each high value reef to achieve sustainability for coral in those regions.

Quarter 2, 2020:

  • Total number of high value reefs managed this quarter: 66
    • Vessel crews conducted manta tow surveillance across 1,501.1 kilometres of high value reef searching for signs of crown-of-thorns starfish activity.
    • Wherever signs of crown-of-thorns starfish activity were detected, cull dive teams were deployed to conduct more in-depth searches.
    • Cull dive teams spent 3,040 dive hours searching for the cryptic, coral-eating starfish and culled a total of 13,012 crown-of-thorns starfish across 2,530 hectares of high value reef.

Tracking ‘Outbreak status’ of reefs

Dashboard description: This interactive display shows the location of individual high value reefs managed by the Crown-of-thorns Starfish Control Program. The map panel on the left shows their ‘Outbreak status’ prior to any pest management for each reef. The map panel on the right shows their ‘Outbreak status’ determined for the reef since pest management action began.

Outbreak status is determined based on the average number of crown-of-thorns starfish observed during manta tow surveys on a reef. Tracking changes in ‘Outbreak status’ provides an indication of progress achieved through pest management over time.

When reefs have ‘No Outbreak’ status (i.e. green dots) it suggests that crown-of-thorns starfish numbers are sustainable for coral growth and recovery. It is important to note that this does not necessarily mean that the reefs are completely free of crown-of-thorns starfish.  For example ‘No Outbreak’ status may be the result of intensive management action to bring crown-of-thorns starfish numbers down to sustainable levels or proactive monitoring which aims to identify crown-of-thorns starfish outbreaks in their initial stages.

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 donut chart and inspect reef level information. Click outside of the map to make donut 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.

Regional breakdown of crown-of-thorns control progress:

  • During this reporting period (April to July 2020) pest management effort focused on 66 high value reefs across the Northern, Central and Southern management regions of the Great Barrier Reef Marine Park.
    • Pest management in the Northern region is important because this is the region of the Marine Park where major outbreaks initially develop.
    • Pest management in the Central and Southern regions of the Great Barrier Reef Marine Park is important because these are the regions that currently have the highest numbers of crown-of-thorns starfish.

Far North:

  • No reefs were managed during this reporting period because previous surveillance showed very few or no crown-of-thorns starfish in this management region.

Northern:

  • 37 reefs in the Northern region were managed during this reporting period in order to maintain ‘No Outbreak’ status and proactively supress the development of an outbreak.

Central:

  • 20 reefs in the Central region were managed during this reporting period, and from the commencement of pest management:
    • 4 reefs have transitioned from ‘Established’ or ‘Severe’ outbreak down to ‘No Outbreak’ through intensive pest management
    • 1 reef (John Brewer Reef) transitioned from ‘Severe’ outbreak down to ‘Established’ outbreak.
    • 15 reefs maintained at ‘No Outbreak’ status through action to supress the development of an outbreak.

Southern:

  • 9 reefs in the Southern region were managed this reporting period, and from the commencement of pest management:
    • 3 reefs have transitioned from ‘Established’ or ‘Potential’ to ‘No Outbreak’ status through intensive pest management.
    • 1 reef has transitioned from ‘Established’ to ‘Potential’ outbreak.
    • 3 reefs have been maintained at ‘No Outbreak’ status through action to supress the development of an outbreak.
    • On 2 reefs, estimates of crown-of-thorns starfish numbers have transitioned from either ‘No Outbreak’ or ‘Potential’ to ‘Established’ outbreaks since initial surveillance. Control efforts on these reefs however have only just begun and these outbreaks are expected to be reduced to sustainable levels in the coming months.

Case Study: Lady Musgrave Island Reef

Dashboard description: The interactive display shows the progress in pest management achieved at Lady Musgrave Island 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. Dots on these maps display the outcomes of individual manta tows around the Reef.

Catch-per-unit effort (CPUE) is tracked over time to assess progress in achieving crown-of-thorns starfish numbers that are ecologically sustainable for coral. The graph on the top right panel shows the trend in catch-per-unit effort over repeated visits to conduct culling at Lady Musgrave Island Reef. The dotted blue line on the graph is the target catch-per-unit effort that promotes coral growth and recovery.

The bottom right panel provides a summary of all the pest management effort that has occurred on this high value reef, as well as action during this particular reporting period.

Interactivity: Hover over dots on the maps to see number of crown-of-thorns starfish observed, crown-of-thorns starfish scars and hard coral cover estimates. Zoom out (scroll) to see the location of Lady Musgrave Island Reef.

Crown-of-thorns control on Lady Musgrave Island Reef

  • Lady Musgrave Island Reef provides an example of the process of controlling crown-of-thorns starfish numbers to levels that are sustainable for coral growth and recovery through intensive pest management.

What was the initial situation?

  • Initial manta tow surveillance at this reef in July 2019 revealed that it had an ‘Established’ outbreak, with a large aggregation of crown-of-thorns starfish along the sheltered back reef slope and also in the lagoon.
  • Initial Reef Health Impact Surveys (RHIS) estimated 36-42% hard coral cover at this reef, and this established a catch-per-unit effort of 0.04 as the ecologically sustainable threshold for coral growth and recovery.

What did the program do?

  • This reef has been intensively culled across 22 repeated visits between July 2019 and July 2020, with divers spending a total of 1060 hours searching and culling 4,833 crown-of-thorns starfish.
  • Between July and October 2019, culling effort was focused along the back reef slope, reducing catch-per-unit effort from 0.18 (i.e. 7.2 crown-of-thorns starfish culled for every 40 minutes spent searching) down to an ecologically sustainable 0.03 (i.e. 1.2 crown-of-thorns starfish culled for every 40 minutes spent searching).
  • Beginning in October 2019, culling effort also targeted the crown-of-thorns starfish aggregation in the lagoon, which caused a rise in catch-per-unit effort up to a peak of 0.16 in December.
  • From January to July 2020, nine additional visits were undertaken and while the target catch-per-unit effort threshold for coral recovery has been mostly achieved there are still some sites requiring continued pest management on this high value reef.

How is the situation now?

  • Repeated manta tow surveillance in March 2020 showed that the reef has been downgraded from ‘Established’ to ‘No Outbreak’ outbreak status.
  • Since March 2020 ‘No Outbreak’ status has been maintained.
  • Smaller crown-of-thorns starfish aggregations are still being identified at this reef and thus intensive pest management is ongoing to reduce crown-of-thorns starfish numbers below sustainable thresholds for coral growth and recovery.

Acknowledgement

The Crown-of-thorns Starfish Control Program is delivered in partnership with the Great Barrier Reef Foundation’s Reef Trust Partnership.