Updated synthesis: What do we know about the North West Banks and Shoals of the Timor Sea?

Submerged reefs and shoals are important features of the North West Marine Region of Australia due to their diverse and often unique benthic (e.g., corals, sponges) and fish biodiversity. In 2009, reefs and shoals near the Montara oil field were exposed to an uncontrolled release of oil and gas that lasted for 74 days.

In response, PTTEP commissioned a new world class body of independent scientific research into the marine life and ecosystems of the Timor Sea. The result is the most comprehensive database ever generated of fish, birds, sea snakes and marine turtles, as well as shoreline and intertidal habitats for this region. These findings are now providing scientists, industry and regulators with a benchmark against which to measure and manage the valuable economic, environmental and social resources of the region. In 2015, PTTEP funded the Australian Institute of Marine Science to make the results of these studies more accessible via the North West Atlas. In 2017, PTTEP funded an additional field survey to create a time series of observations at three of the shoals, and to provide an updated synthesis of all the data via the North West Atlas. This synthesis is provided below (read the full report).

How did habitat change over time at each shoal?

Click on the circles for a given year for a shoal to see how much of the live habitat on that shoal was made of hard coral, soft coral, sponge, algae, or seagrass. For example:

• Algae was the most widespread type of live habitat found on each of the shoals in each year. Its relative cover was highest in 2013, when it reached 70% of Vulcan Shoal's live cover.
• Seagrass cover at Vulcan Shoal dropped from ~29% in 2010 to ~18% in 2011 to ~4% in 2013. It then increased to ~3% in 2016. At the other shoals, seagrass cover was stable over time at around 6%.
• Hard coral cover at Goeree Shoal dropped from ~15% in 2011 to ~5% in 2013 due to wave damage from severe tropical cyclone Lua in 2012, and then recovered to ~14% by 2016. Similar drops were seen at the other shoals, with less recovery. [Cyclone wave energy can dislodge, break and bury hard corals.]

Note that the values on the charts do not add up to 100% because none of the shoals was ever completely covered (100%) by live habitat. For example:

• In 2011, live habitat cover was the most extensive (~49%) on Goeree and least extensive (~46%) on Vulcan. In contrast, in 2013, live habitat cover was the most extensive on Barracouta East (~36%) and least extensive (~27%) on Goeree.
• The total % of live habitat cover dropped on each of the shoals between 2011 and 2013 due to large waves generated by cyclone Lua; and recovered by 2016. [Cyclone wave energy can dislodge, break and bury hard corals; rip soft corals; dislodge and tear sponges; dislodge and tear seagrass; initially scour algae from the shoal surface, but also create space for it to take over from corals.]

How did the number and number of types of animals seen change over time at each shoal?

From footage collected using BRUVS (baited remote underwater video stations), we count the number of each species (different types of animals) that we see at any one time for each site. Species richness is the number of different types of animals that we counted from the BRUVS, and abundance is the total number of any type of animal that we saw. Below we show the average species richess and average abundance across each shoal.

From the above, we see that more individual species and more individual animals of a given species were seen at Barracouta East Shoal compared to the other shoals every year. This may reflect the higher total % of live habitat measured on Barracouta East versus the other shoals in every year except 2016 (% in the white 'doughnut hole' of each graph above).

We also examined how the average abundance of the most commonly seen types of animals changed over time on the three shoals: bony fish and sharks.

• We saw many more types and numbers of bony fish than sharks at every shoal.
• The abundance of sharks changed more from year to year than the abundance of bony fish.
• Bony fish were less common at Vulcan shoal than the other shoals. This may relate to the consistently lower % of hard coral seen there compared to the other shoals, and the nearly complete loss of a seagrass meadow in 2013.
• Shark abundance dropped at Barracouta East shoal from 2011 to 2013 due to a loss of whitetip reef sharks, possibly from the loss of hard coral cover.
• Grey reef sharks became more common at Goeree shoal through time.
• We only saw silvertip sharks at Vulcan Shoal, where tiger sharks were also more commonly seen.

 

Video footage from BRUVS over time

Click on the videos below to get a glimpse of sea life at Barracouta East, Goeree and Vulcan shoals in 2011, 2013 and 2016. Our analysis based on the data from these videos shows that sea life has remained stable at the shoals over the past 5 years.

2011

2013

2016

Where were BRUVs videos taken on each shoal?

Each BRUVs drop location is shown by a grey square on the interactive maps below for Barracouta East, Goeree and Vulcan shoals. Red squares show which BRUVs drops were used to create the videos provided above. Click on any red square and scroll to the far right in the box that pops up to see which year and location it was taken (as contained in its file name).

Barracouta East

Goeree

Vulcan

All shoals surveyed for PTTEP, 2010-2016

The red dots on the map below show all the BRUVs drops completed at all nine shoals surveyed for PTTEP over the period 2010 to 2016. Click on each dot to see the name of the shoal and when the drop was completed. You can see example videos from each shoal in the earlier content on the NW Atlas- Synthesis: What do we know about the NW banks and shoals of the Timor Sea? Click on the shoal of interest and go to the Video tab to see each video.

 

Learn More

• Read about the shoals in the book Big Bank Shoals of the Timor Sea: an Environmental Resource Atlas
• Download the 2016 Field report
• Download the 2013 Report of Research
• Download the scientific monitoring studies:
  • Marine Megafauna Aerial Assessment Surveys (study S1)
  • Shoreline Ecological Assessment Aerial Surveys (study S2)
  • Assessments of Fish Catch for the Presence of Oil (study S3)
  • Assessments of Effects on Timor Sea Fish and Fisheries (study S4)
  • Offshore Banks Assessment Surveys (study S5)
  • Shoreline Ecological Ground Surveys (study S6)
  • Oil Fate and Effects Assessments (study S7)
  • More about the Montara oil spill