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After the Oil Spill

oil spill

The oil spill at Montara lasted for 74 days.

By Asa Wahlquist

Just 4 years after the Montara oil spill, scientists have compiled the most detailed description yet of the wildlife, fish and habitats of the Timor Sea as they monitor the recovery of the species affected by the spill.

Dozens of scientists and researchers have produced a scientifically rigorous set of findings on turtles, sea snakes and commercial fish species of the Timor Sea; on bird populations; on corals and mangroves; and on Australia’s the north-west coastline, as well as an array of tiny islands, shoals and cays.

This scientific research – undertaken as part of the Montara Environmental Monitoring Program – was instigated as a result of an oil spill that occurred on 21 August 2009 and lasted for 74 days. The research was funded by petroleum exploration and production company PTTEP Australasia in cooperation with the federal Department of the Environment.

Montara is located 180 km from the Australian coast. The spill led to the release of an estimated 30,000 barrels of oil. The light orange oil was more water-soluble than the familiar black crude; 99% of the oil remained within 82 km of the spill site. Most of its toxic elements were gaseous and quickly evaporated.

As part of its response to the oil spill, PTTEP collaborated with a range of Australian authorities and organisations, quickly commissioning a unique cross-institutional team of scientists to build the most accurate, detailed and fully independent account possible of the fate, impact and influence of the spilled oil.

No oil reached the Australian mainland or Indonesian coast. The closest recorded from Australia was 35 km; the closest recorded from Indonesia was 94 km.


Fish of the Timor Sea

A key focus of the research was on fish, partially due to the spill occurring in a commercially important fishing area. The Western Australian Department of Fisheries studied the effects of the oil spill on four main commercial fish species: goldband snapper, red emperor, saddletail snapper and yellow-spotted rock cod. It sampled fish from affected areas and non-impacted areas in November 2009, when there were still visible oil slicks on the sea surface, and then again in January 2010.

The researchers found no detectable petroleum hydrocarbons in the fish muscle samples, and concluded that the fish species from the samples used in the study would probably have been safe to eat.

They pointed out that the samples were taken after the oil stopped flowing and cautioned that the results “cannot be extrapolated directly to the period when oil was actively flowing”.

In another fish assessment study, Curtin University’s Dr Christopher Rawson and Associate Professor Marthe Monique Gagnon presented raw and cooked fillets from deep water species captured in the area to a panel of professionals trained in using olfactory analysis to assess the impact of chemicals on food. Olfactory analysis is based on the principle that the human nose is an extremely sensitive instrument for identifying food taint.

There were some detectable olfactory differences in red emperor sampled in November 2009, the first of the three sampling periods. However, there were no distinctive taints related to the presence of oil or dispersants. The researchers said it was difficult to say whether the assessors regarded the fish samples taken near Montara were of better or worse quality than those collected further away.

There were no differences detected in the goldband snapper samples or the later red emperor samples.

In a third study of fish, Gagnon and Rawson reviewed biomarkers in goldband snapper and red emperor, and two species that live nearer the surface, Spanish mackerel and rainbow runner. They sampled the fish four times in the 15 months following the spill.

Biomarkers measure the impact of chemicals like hydrocarbons through biological endpoints like liver detoxification enzymes, which increase when the animal is exposed to contaminants. Other biomarkers included biliary polycyclic aromatic hydrocarbon (PAH) metabolites, which are a very sensitive indicator of exposure to petroleum hydrocarbons, liver integrity and oxidative DNA damage.

Gagnon and Rawson found that a small number of fish caught in November 2009 had metabolised petroleum products, but they only detected “limited ill effects”. The affected fish had increased liver size, high biliary PAH metabolites (which indicated uptake of petroleum) and some increased DNA damage. No reproductive damage was observed.

Nineteen months after the spill began, fish caught close to Montara showed continuing exposure to petroleum hydrocarbons, with enlarged livers and elevated oxidative DNA damage. Two years later, biomarker levels had returned to reference levels, with the exception of the liver size, which was larger in fish collected close to Montara.

Reefs and Shoals

The nearest land masses to the Montara well-head are the submerged Vulcan and Barracouta shoals. Dr Andrew Heyward from the Australian Institute of Marine Science found no obvious signs of recent disturbance at the two shoals 6 months after the spill. In this fourth study relevant to fish health he concluded that the effect of the spill on fish was weak to negligible.

While there was widespread presence of oil at some sites, it was too severely degraded to be matched to Montara oil, although the spatial pattern was consistent with the Montara spill. The oil was in concentrations several orders of magnitude lower than levels at which biological effects are expected.

Heyward found that within 50 km of Montara, fish species diversity and abundance declined marginally, and smaller fish abundance declined. It was possible this was due to exposure to oil and/or dispersants, but without pre-spill baselines that conclusion could not be drawn.

In 2011, the abundance of fish and fish species richness in the nine shoals was estimated to be 1.25–3 times higher than equivalent shoals in the Great Barrier Reef Marine Park.

Heyward’s team also studied the possible effects of the spill on coral at Ashmore Reef and Cartier Reef and at the unaffected Seringapatam Reef. The reefs host a vivid display of more than 50 species of coral.

The first survey, in April 2010, found no evidence of recent major disturbance, with the exception of a minor coral bleaching event that was worst at the most distant reef and probably caused by higher water temperatures. The coral recovered the following year.

Laboratory analysis of sediment samples detected some hydrocarbons at all three reefs. The levels, even at Ashmore and Cartier Reefs, where they were higher, were below the point at which they would pose a risk to the environment. Fewer hydrocarbons were detected in the 2011 samples.

Studies have also shown there is a previously existing background presence of petroleum hydrocarbons in the Timor Sea. They could originate from the oil industry, passing ships, discharge from fishing boats and from naturally occurring oil seeps in the region.

The patterns of coral reproduction and recruitment between 2010 and 2011 at all three reefs were similar. The percentage of new live hard coral recruits was similar to the Great Barrier Reef.

Sea Snakes and Turtles

Dr Michael Guinea of Charles Darwin University made two surveys of sea snakes and marine turtles in March 2012 and 2013. He found no detectable impact of the spill on the sea snakes and marine turtles.

But the sea snake population presented some mysteries. It used to be highest at Ashmore Reef, but it started falling in 1998 and none have been seen there for some years. The decline began long before the Montara incident. The two other reefs closest to Montara – Hibernia and Cartier Island – had the highest species diversity and the greatest number of individuals.

Seabirds and Shorebirds at Ashmore Reef

Birds are very vulnerable to oil exposure. For many years Dr Rohan Clarke of Monash University has been studying the seabirds and shorebirds at Ashmore Reef, which is an ecological refuge of international significance. It hosts over 20 breeding species and is visited by 16 species of seabird or birds that spend most of their lives at sea. Clarke found no signs of oil, but he did find that bird numbers were increasing. In April 2010 there were 75,000 seabirds and by April 2013 the number reached nearly 108,000.

Coastline and Mangroves

In November 2009, Dr Norm Duke, who is now with James Cook University, and his team surveyed the 5102 km of coastline from Darwin to Broome. In the first detailed survey of the region his team discovered that the mangroves and tidal wetlands were more extensive than expected, and they found twice as many estuaries than had been previously mapped.

The team observed significant numbers of dolphins, dugong, whales, turtles, crocodiles, sharks and rays, and more signs of turtle nesting than expected.

Scientific Legacy of the Montara Spill

The research determined that the oil spill’s measurable impact on the environment and the biota of the area around Montara was extremely low. The most significant consequence was the comprehensive database developed by the Montara Environmental Monitoring Program, which has created a baseline to measure future changes in the surveyed environment whether they come from cyclones, commercial activity or climate change.

A legacy of the research is the most comprehensive database ever generated of fish and birds, of sea snakes and marine turtles, of shoreline and intertidal habitats and their conditions, for this region. It has contributed knowledge to the variability of the environment, how it changes over time and how natural resources are affected by human stresses.

This increased knowledge is enabling more certainty in assessing and predicting impacts from industry; assisting industry and government assessment of conservation and environmental values; enabling better planning of activities and risk mitigation measures; and helping cultivate a greater understanding of biodiversity in the Timor Sea.

Asa Wahlquist is a freelance writer who has won a Walkley Award for Rural and Regional Journalism and a Eureka Prize for Environmental Journalism.

An extensive summary of the Montara research can be found at, and the full research papers can be found at