On 5 October 2011, Maritime New Zealand was called to respond to an ‘incident’ in the early hours of the morning. The 236 m cargo vessel Rena had struck the Astrolabe Reef about 12 nautical miles off the coast and was stuck fast. Fortunately, there were no reported injuries to the 25 crew onboard. However, New Zealanders watched with horror over the next weeks as the stranded foreign ship, carrying 1368 containers, 1700 tonnes of heavy fuel oil and about 70 tonnes of diesel in its tanks, slowly split and spilled hundreds of tonnes of thick fuel oil and dozens of shipping containers into the sea causing death and sickness to wildlife and polluting New Zealand’s pristine Bay of Plenty coastline.

Dealing with the oil

The Rena had around 1700 tonnes of oil aboard when the vessel struck the reef. Over 350 tonnes was spilled into the ocean, with most of the remaining oil pumped from the vessel into tankers.

Using dispersants

Initial efforts to deal with the oil included using a dispersant (like a detergent) called Corexit 9500 to try to break up the oil slick stretching 5 km northwest from the ship. According to Maritime New Zealand, this produced “inconclusive” results. Some scientists have been critical of the use of dispersants, believing they may cause more harm than good. Guidelines on the use of dispersants written for the government by the research institute Cawthron in 2000 cautioned that a dispersant response had to be assessed to determine whether it would result in a “net environmental benefit”. In an interview with the Science Media Centre, marine ecologist Dr Mark Costello, Associate Professor at Auckland University’s Leigh Marine Laboratory, said, “Dispersants, like a lot of detergents, will kill animals and plants as well. Some of the new ones may be safer, but I don’t know how safe they are.”

University of Southampton lecturer in oceanography Dr Simon Boxall, who has experience of the Erika oil spill on France’s Brittany coast in 1999 and the MV Braer oil spill in the Shetland Islands in 1993, says dispersants do have a role to play but only in a few cases. There is a tendency to use them regardless.

“They are more harmful than the oil itself, and they are not less toxic than dishwashing liquid! Fairy dishwashing liquid doesn’t carry hazchem advice, and you don’t wear protective clothing and masks to do the washing up. In their raw form, some dispersants can be very toxic, and I believe will do more harm than good. Most of the Corexit dispersants were banned from use by the UK Government in 1998 for rocky shore areas and can only be used offshore after consultation with government and if no alternatives are available. Sweden has a blanket ban on all dispersants in the marine environment. In this case – with limited knowledge of the region – I’d advise caution on use of dispersants.”

However, in a later interview, Dr Boxall said Corexit 9500 is one of the less-toxic dispersants, and the volume used (3191 litres) should not cause undue concern.

Manual removal of oil from beaches

The New Zealand Defence Force as well as an army of volunteers mobilised to manually remove oil from the beaches. This involved scooping up black globs from the sand and stuffing them into rubbish bags, as well as manually scraping oily residue from rocks. Sandy beaches were also manually sieved to capture any smaller globs of oil. The work cost New Zealand thousands of man hours and millions of dollars.

Introducing microbes

Another option that was considered for any oil that escapes this manual clean-up is microbes that ‘eat’ the oil. These can occur naturally in the environment, especially in warmer climates, but there is also some experimental science showing they can be introduced and encouraged to multiply.

Dr Costello explained, “[Effectiveness of the microbes] seems to depend on what type of oil it is and what type of environment it is, as the physical environment breaks it into smaller pieces... You do get natural oil and gas leaks in various parts of the world. The marine microbes that break down oil slicks seem to be pretty cosmopolitan, and they break down lumps of oil in other places.

“I know people have sprayed nutrients such as nitrogen on beaches to try and speed up the growth of bacteria that would help degrade the oil – but as far as I know, this has been experimental, and it’s not yet clear whether it has any effect in degrading the oil faster. The nutrients could have their own knock-on effect.”

Dr Boxall said that microbe activity will act quickly and break up the oil that is naturally dispersed in about 4–6 weeks given current temperatures and increasing daylight.

“Nature did a lovely job of Braer, and very little human intervention took place [no dispersants were used]. The Erika involved substantial mechanical beach clean-up, but we did a study 5 months after the spill, and levels of hydrocarbons on the beaches of France that had been impacted were below background levels – and in fact were better than one or two control beaches. The Rena spill needs containment as first priority, booming where possible to contain the marine-based oil. Beach clean-up will be important as the oil breaks down more slowly on the beach than at sea. At sea, nature will disperse and break the oil down very quickly, without use of chemicals

Other equipment used by Maritime New Zealand to deal with oil spills includes booms to prevent oil spreading, skimmers to remove the oil from the water surface and sorbents – materials that either soak up oil like a sponge or can attract oil to stick to them.

Removing small quantities of lubricant oils left onboard was relatively straightforward (weather permitting) with the freer-flowing liquid pumped onto waiting tankers. However, removing the fuel oil left in the Rena’s tanks was more complicated. Rena’s fuel oil is very thick, like tar on the road, and it has to be heated to make it runnier before it can be pumped onto waiting tanker ships. Despite this, the tankers managed to capture most of the fuel oil.

Bad weather causing rough seas was an on-going problem for the team trying to deal with the wreck. When the sea is too rough, it is not safe for people to work onboard or for tanker ships to get close enough to pump off the remaining oil.

Dr Boxall said the stormy weather is both a pro and a con. “The bad news is that it hampers the clean-up and access to the stricken vessel. The good news is that it helps the oil disperse naturally. A good example of this was the Braer spill off the Shetlands... very large volumes dispersed very quickly by heavy storms.”

Non-oil problems

When the weather is fine, another problem faced by the salvors (people who salvage vessels and cargos) is the smell of rotting perishable cargo. 121 of the containers still onboard are known to contain perishable food goods. The stink of these goods rotting onboard is so bad that the noxious fumes are being tested regularly to make sure it is safe for people to work there.

Containers that have fallen from the ship have become shipping hazards, with some floating unseen just below the surface. At the time of writing, 58 of the 88 containers lost overboard were still unaccounted for, and one of these contains the hazardous material – alkysulphonic liquid class 8.

Impacts on wildlife

At the time of writing, Maritime New Zealand has reported that more than 1300 birds have been found dead since the oil spill. Forest & Bird report that this death toll is likely the tip of the iceberg, as many oiled birds would have sunk into the ocean.

In addition, many of the birds that nest in the area are likely to have lost this breeding season, making the impact of the Rena go far beyond the time when all the oil is finally cleaned up.

Experts are working to identify what bodies have been recovered. This is not an easy task, as some of the birds are literally stuck together in tarry clumps like you would find on chip-sealed roads.

To date, birds from 23 species have been indentified. These include:

  • 458 diving petrels
  • 198 fluttering shearwaters
  • 92 Buller’s shearwaters
  • 38 white-faced storm petrels
  • 20 little blue penguins.

A small number of rare species have also been found dead including mottled petrels, blue petrels and Antarctic prions. Conservationists are particularly fearful for the area’s 100-strong dotterel population – only 1500 are left in the world.

Oil affects seabirds by coating their plumage in sticky, tarry slime. A bird’s feathers are precisely aligned with the help of tiny barbs – if you’ve ever played with a feather, you will have noticed how the barbs hook together to form the vane (the flat soft part on both sides of the central shaft). This helps the bird to have a waterproof coat and traps air pockets under its feathers for buoyancy and warmth. When a bird is coated in oil, the feathers become matted and misaligned, causing the bird to lose body heat and exposing it to fatal temperatures and weather conditions. They can also lose their buoyancy and, in exhaustion, sink and drown.

An oiled bird might also preen excessively in an effort to remove the oil. When they do this, they can swallow the toxic sludge, which can fatally poison their kidneys, liver, lungs, intestines and other internal organs.

The energy required to move and excessively preen when oiled can simply cause some birds to drop dead of exhaustion, dehydration or starvation.

If birds are pregnant at the time of ingesting any oil, the shells on their eggs can be thinner and can break more easily. If oil gets on any laid eggs, it can suffocate the unhatched chicks.

Although the full impacts from the Rena are not yet known, an area that has suffered an oil spill can end up with a contaminated food supply as the toxins are absorbed into the ecosystem. This limits the ability of the surviving population to sustain itself.

On a positive note, the National Oiled Wildlife Response Team has rescued and cleaned over 400 surviving oiled animals at the wildlife centre, where they are being nursed back to good health. Many of the birds were suffering from dehydration and hypothermia when they arrived and no doubt would otherwise have perished.

Charges laid

Two investigations into the Rena pile-up on the reef are continuing, with the Master (Captain) and Second Officer (Navigator) charged with “discharge of harmful substances from ships or offshore installations” and “for operating a vessel in a manner causing unnecessary danger or risk”.

Members of the public who find containers on the beach are asked to call 0800 OIL SPILL (0800 645 774), unless the containers are tagged to show that they have already been identified. Maritime New Zealand says people should not touch the containers or their contents, as they may be hazardous and they also belong to someone.
 

Useful links

For further information on the Rena disaster, go to Maritime New Zealand’s website.

    Published 16 November 2011