Montara oil spill - Scientific monitoring studies

Scientific monitoring studies

Disclaimer
The views and opinions expressed in these studies are those of the authors and do not necessarily reflect those of the Australian Government or the Minister for the Environment and Energy.

While reasonable efforts have been made to ensure that the contents of these studies are factually correct, the Commonwealth does not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of these studies.

The focus of scientific monitoring is to provide information that is used to estimate environmental damage and recovery. There were seven scientific monitoring studies under the environmental monitoring program:

As specified in the Monitoring Plan, unlike operational monitoring, each scientific study had triggers associated with their implementation. Information on whether these triggers were met was provided by the results of operational monitoring studies and other scientific monitoring studies. Six of the seven scientific monitoring studies were implemented on the basis that their triggers were met. Further information can be found below.

Scientific Monitoring Site Locations

The scientific monitoring studies were conducted on sensitive reefs, islands, shorelines and in oceanic waters in close proximity to the Montara well. The locations of scientific monitoring sites in relation to the Montara well are shown below.

Map showing the location of the Montara Well

Marine Megafauna Assessment Surveys

Marine megafauna assessment surveys were designed to identify the diversity and abundance of marine wildlife, including whales and dolphins, in the region to determine the level of exposure to oil.

The triggers associated with the implementation of this study were:

  • observed proximity of marine megafauna to oil slick or response operations combined with suggestion of significant harm (i.e. not an isolated incident); or
  • observed incident of harm attributable to oil or the response.

While daily aerial and vessel-based surveillance observed dolphins in the vicinity of the oil spill, no confirmed reports of impacts were received; therefore this study was not triggered.

Shoreline Ecological Assessment Aerial Surveys

This study aimed to identified and assessed the habitats and wildlife along extensive shorelines in the region of the oil spill. The study was based on aerial surveys; however, where necessary, support vessels could be used.

A team from the University of Queensland undertook a shoreline assessment survey of the Kimberley coast between Darwin and Broome in November 2009. This survey collected baseline information on the habitats and species along the coast before any potential oil impact occurred. If oil had reached the Kimberley coast, the results of this study would have helped identify any impacts so they could be appropriately addressed. The study found no signs of oil impacting on marine wildlife or to the habitats that were surveyed. During the study, marine turtles were the most commonly sighted sea creatures although whales, dolphins, dugongs, crocodiles, sharks and rays were also seen. The study found that a large proportion of the intertidal habitats, such as mangroves and estuaries, along the coast would be sensitive to oil had it reached the Australian shore.

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Assessment of Fish Catch for the Presence of Oil

This study assessed the level of oil impact on commercial fish catch in the region and determine whether the catch acquired a taint or became unsafe to eat. The report for this study is now available:

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Fish were collected during two sampling trips in November 2009 and January 2010. Gut and tissue samples were tested for the presence of hydrocarbons. No hydrocarbons were detected in fish tissue at any time. One gut sample contained traces of hydrocarbon, though the amount present was too small for the source of the hydrocarbon to be positively identified. The report concludes that the fish sampled would probably have been safe to eat. However, it should be noted that samples were taken after the Montara spill was capped and these results cannot be extrapolated to the period during the spill.

In addition, an olfactory assessment study was carried out; olfactory assessment, or "sniff testing", of seafood has been established as a sensitive technique for identifying taint by petroleum products even when the product is considered "acceptable" in terms of food safety.

This report is now available:

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Samples from two commercially-important species (Red Emperor and Goldband Snapper) were collected from nine locations within the Timor Sea during three research expeditions. Trained panelists from the seafood industry carried out an olfactory analysis for each sample in both a raw and cooked state to determine if they could identify and describe any difference between samples from impacted and non-impacted sites.

During the first sampling trip in November 2009 - immediately after the Montara well was capped - panelists were able to distinguish between the Red Emperor samples (but not in the Goldband Snapper samples) taken from impacted sites and the samples taken from non-impacted sites. The differences were observed in both raw and cooked samples of the Red Emperor samples.

All descriptors used by the panelists to describe the samples from the impacted site could also be used to describe "normal" fish odours and there were no consistent descriptions that would indicate the presence of particular contaminants. It was not possible to conclusively identify the source or sources of these olfactory differences. It is unknown whether the difference noted between samples from impacted and non-impacted sites is attributable to exposure to hydrocarbons or arises from site-specific characteristics unrelated to the Montara spill. No differences were detected in any samples from the two later sampling trips.

Assessment of Effects on Timor Sea Fish and Fisheries

This study identified the impacts of oil on Timor Sea fish and fisheries. It had two components, assessments of short-term effects on Timor Sea fish and fisheries (S4A) and assessments of long-term effects on Timor Sea fish and fisheries (S4B).

S4A assessed the geographical extent of fish exposure to oil and determined if fish health, including reproductive health had been affected. S4B has a number of objectives - for example, identifying change in species composition, long-term effects on target species or indirect effects such as impacted plankton communities.

Two reports for study S4A are now available:

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This study targeted two demersal species (Goldband Snapper and Red Emperor) and two pelagic fish species (Spanish Mackerel and Rainbow Runner). Biopsy samples of these species were collected at a range of sites during three research cruises and a range of biological investigations, including physiological indices and measurement of biochemical markers, carried out.

Fish collected during Phase I and II of the monitoring showed evidence of exposure to petroleum hydrocarbons at sites close to the Montara well - increased liver size and occasionally increased oxidative DNA damage. While at some sites the differences in biomarker levels were still observed one year after the end of the well release (Phase III), the magnitude of the differences had reduced relative to earlier samplings - suggesting a partial, ongoing trend toward a return to normal biochemistry/physiology following exposure to petroleum hydrocarbons.

Phase IV of this project was commissioned to investigate the apparent trends in two demersal fish species (Red Emperor and Goldband Snapper) noted in Phases I-III. Phase IV results confirmed the trends shown in Phases I-III: biomarker levels, including liver detoxification enzymes, PAH biliary metabolites and oxidative DNA damage, were comparable between impacted and reference sites in both species. As in Phases I-III, relative liver size was shown to be higher at sampling sites closest to the Montara wellhead. Reproductive health, as indicated by relative gonad size and egg maturation, was shown to be normal.

Phase IV of this study also indicated possible ongoing exposure to hydrocarbons at one location (around Heywood Shoal) most likely corresponding to known natural hydrocarbon seeps.

The work done through study S4A provides a valuable baseline for ongoing monitoring associated with future production of the Montara field.

Following discussions with CSIRO and the Department, it was determined (by PTTEPAA) that there was insufficient relevant data on which to base a targeted monitoring program to examine any potential long term impact of the spill on relevant fish stocks (Study 4B). In addition, other studies comprising the Montara Spill Monitoring Programme that have assessed the potential impact on fish indicate that it is extremely unlikely that there would be any impact at a fish stock level. The intent of Study 4B was that any fisheries monitoring program would be developed in a phased manner and would only proceed if it could be justified.

Offshore Banks Assessment Surveys

Offshore banks assessment surveys identified and assessed the level of impact to the sediment and marine life of submerged marine banks in the region of the oil spill. Three surveys were undertaken (2010, 2011 and 2013).

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The 2010 surveys included a pilot study to provide baseline information and developed methods for future monitoring.

There were no obvious signs of a major recent disturbance found at either the Barracouta or Vulcan shoal. The study found that both shoals contained diverse communities of flora and fauna and there were pronounced differences in the abundance of species within and between the shoals. This report is a preliminary study for the Offshore Banks Assessment Surveys (study S5). The study's findings provide important baseline information for future monitoring work that will be conducted as part of the Montara environmental monitoring program.

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The 2011 surveys built on the pilot study to develop a comprehensive understanding of the banks and shoals in the region. Nine banks and shoals were investigated during this study, ranging in distance from within three kilometres to around 150 km from the Montara well. At each bank and shoal, sediment samples were collected to investigate exposure to hydrocarbons, multi-beam swath mapping was undertaken to determine the depth and substrate-type, and remote video and photography was used to investigate benthic habitat and fish communities.

The sediment sampling showed a widespread presence of highly degraded oil at low concentrations. Owing to natural degradation, the oil detected cannot be positively identified. It was not possible to determine conclusively which hydrocarbons originated from the Montara well and which originated from other previously documented sources (such as natural seeps). Irrespective of the source, the levels identified in all samples were very low and significantly lower than would be expected to cause biological effects.

Across the shoals, there were no obvious signs of a recent major disturbance to biological communities, with one exception: at Vulcan Shoal, the closest shoal to the Montara well, a very significant loss of seagrass occurred since the pilot survey. The cause of this loss cannot be determined, and it is not possible to rule out a link to the Montara spill. However, remaining seagrass communities appeared to be healthy during the surveys (six months after the Montara spill), and a highly delayed effect is considered to be unlikely.

The variability between shoals is most likely to be strongly influenced by natural processes. The patterns in fish community structure across the shoals indicate that the Montara spill may have had some influence, but no impacts can be definitively identified.

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The 2013 survey built on previous surveys to characterise multi-year trends in ecological assemblages (benthos and fish) to understand natural variation and investigate any long-term impacts linked to the Montara oil spill. Three of the nine previously-surveyed shoals (Barracouta East Shoal, Goree Shoal, Vulcan Shoal) were revisited in 2013.

The study highlights that these shoals are highly diverse and subject to high levels of natural variability affecting both benthic and fish assemblages. It is not possible to distinguish between impact from the Montara oil spill and natural variability due to the lack of pre-spill baseline data.

There was decline in coverage in most benthic biota – and a corresponding increase in coverage of macroalgae, sand/silt and rubble – at broad scales across the three shoals compared to previous surveys. The seagrass loss noted at Vulcan Shoal in 2011 had not recovered. In addition, an unusual soft-coral community at Barracouta East Shoal that was noted in 2010 and 2011 was absent in 2013. The broad scale of these general and specific declines indicate that the area has been subject to a major scouring event (possibly a large storm). Analysis of long term trends highlight that benthic assemblages on these shoals are subject to high natural variability.

Changes in fish community structure varied between shoals, but differences were relatively small compared with variation between shoals noted in the 2011 and 2013 surveys. As with the 2011 surveys, the patterns suggest that there may be some influence from the Montara spill, but it is not possible to discern this from high natural variability.

Shoreline Ecological Ground Surveys

Shoreline ecological ground surveys assessed the actual and potential impacts of the spill to shoreline plants, animals and habitats through ground surveys of sensitive reefs, islands and shorelines.

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There were no signs of oil contamination found during the survey. The report does not draw conclusions about the long-term effects of the Montara well release; rather, it identifies the potential for long-term impacts on bird populations and establishes a monitoring protocol and a robust baseline dataset to inform ongoing monitoring efforts. The report also provides detailed information concerning individual seabird species at Ashmore Reef and how aspects of their biology relate to the potential for long-term impacts.

After the initial post-impact field survey, a monitoring program for seabirds, shorebirds and vegetation condition was implemented for Ashmore Reef, Cartier Reef and Browse Island. The surveys began in 2010 and were conducted twice a year–every April and November— for a period of five years.

There is no evidence of significant impact on seabirds and shorebirds in the Sahul Shelf region from the Montara oil spill. The numbers of seabirds recorded in post-impact surveys was larger than previously recorded and declines in numbers of shorebirds reflected ongoing declines throughout the East Asian-Australasian Flyway.

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Coral bleaching was seen at all three reefs. The study found that the bleaching was most likely due to higher than normal sea temperatures, based on temperature data collected during the survey and because highest levels of coral bleaching was found at control site. However; further studies to determine if the oil spill has had any impact on Ashmore and Cartier Reef Reserves' resilience to bleaching are underway.

Although the possible effects of any oil contamination on coral reproduction were not able to be tested the study found no signs of recent major disturbance to the coral reefs at Ashmore and Cartier. Further studies are being conducted to determine if the oil spill had any impact on coral reproduction at Ashmore and Cartier Reef Reserves.

Hydrocarbons were found in sediment samples collected from Ashmore and Cartier Reefs Reserves as well as the control site, Seringapatam Reef. The hydrocarbons found in samples collected from the reserves were positively identified as degraded crude oil which differs from the types of hydrocarbons found at Seringapatam. This finding supports sightings during the incident response of oil residues at Ashmore and Cartier Reefs. Natural hydrocarbon breakdown means that the source of the crude oil found at the reserves cannot be positively identified. Further studies are being conducted to provide more information on the hydrocarbons found in sediment samples at all three reefs.

A follow up study was carried out in 2011:

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This study built on previous work to investigate the ongoing state of reef communities as well as examining other aspects of reef health, including coral reproduction and fish community diversity. Surveys were carried out at the two closest emergent reefs to the Montara well, Ashmore Reef and Cartier Island (167 km west-north-west and 108 km west from the Montara well respectively), as well as Seringapatam Reef (296 km south-east from the Montara well and far from modeled oil trajectories).

The surveys showed that the overall composition of the reef communities remained consistent between 2010 and 2011. Average live coral cover increased at all three reefs at a modest rate. The coral bleaching event that was observed during the previous study was largely absent in this study. There was no evidence of a broad disturbance that correlates with impacts from the Montara spill.

The study confirmed that coral reproduction and recruitment was occurring as expected at all three reefs and patterns of juvenile coral abundance at all three reefs was considered normal. The fish surveys showed that fish communities at Seringapatam reef were significantly different to those at Ashmore and Cartier reefs, suggesting a history of disturbance mostly likely from cyclones and coral bleaching events. There were no obvious patterns identified in the fish community surveys that indicated an impact from the Montara spill.

Hydrocarbons were recorded in fewer sediment samples, and at lower concentrations, than in the 2010 survey. A pattern of higher hydrocarbon concentrations was found at Ashmore Reef. Natural hydrocarbon breakdown processes are occurring and the degraded state of the hydrocarbons prevents identification of their source. For all samples, the measured concentrations of hydrocarbons were significantly below levels that national guidelines identify as a risk to the environment.

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This study quantified the presence of sea snakes and marine turtles in areas of the Sahul Shelf that were impacted by the Montara oil spill. Six reefs (three 'impacted' and three 'unimpacted') were surveyed in 2012 and 2013; an additional 'unimpacted' reef was surveyed in 2013. Abundance and diversity of sea snakes and turtles were recorded using a range of direct observation methods. Blood samples were collected from foraging sea turtles at one 'impacted' site and one 'unimpacted' site to investigate potential contamination of diet. Turtle nesting activity was also recorded at sites with islands and cays. In addition, beaches, coral reefs and seagrass beds were inspected for any evidence of hydrocarbon contamination. Data collected during these surveys was compared to data collected during previous studies (prior to the Montara spill).

There is no evidence of the Montara spill having a long term impact on sea snakes or marine turtles in the Sahul Shelf region, however the limited baseline information, especially on sea snake populations, preclude ruling out any impact. The study highlighted the dynamic nature of sea snake populations in the region. There was no evidence of hydrocarbon residue on beaches, coral reefs or seagrass beds at any of the study sites.

Oil Fate and Effects Assessments

Oil fate and effects assessments aim to determine the distribution of oil during the incident and the potential concentrations of oil in the water column as a result of chemical dispersant spraying operations. This study has been triggered and the results are available.

The study found that most of the area affected by the oil was within 82 kilometres (or 44 nautical miles) of the Montara well head and the spill was predominately contained within Australia's exclusive economic zone. A small quantity of oil entered Indonesian waters, which was reported to relevant Indonesian authorities during response operations. The study also found that under the worst case scenario dispersed oil from three spraying operations may have reached the Goerree and Barracouta shoals. Because of these findings, a further study—the Scientific Monitoring Study 5 Offshore Banks Assessment Survey—will be undertaken.

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