Wilderness Society report shows spill would likely affect fishing and tourism, and threaten whales, seabirds, sea lions and sea turtles, along the southern coast

An oil spill from BP’s planned drilling in the Great Australian Bight could affect most of Australia’s southern coastline, shutting down fisheries and threatening wildlife including whales, seabirds and sea lions, new modelling has shown.

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BP plans to drill the first of four exploratory wells off the South Australian coast next year and submitted an environmental plan (pdf) for approval to the National Offshore Petroleum Safety and Environmental Management Authority last week. A decision is expected this month.

Oil spill modelling commissioned by the Wilderness Society found that a failure in BP’s deep sea drilling would probably prove calamitous to wildlife and the fishing and tourism industries, causing up to 265,000 sq km of ocean – about three times the size of Tasmania – to contain enough oil to close fisheries.

Even under a “low-flow” oil spill – 5,000 barrels a day spewing into the ocean – oil would flow to Western Australia and Victoria, the analysis found.

A worse scenario of 50,000 barrels of oil a day, slightly less than BP’s disastrous Gulf of Mexico oil spill in 2010, would have oil stretching throughout the Bass Strait and a 10% chance it would reach the coast of New Zealand.

In summer the oil would drift towards Western Australia’s whale areas and in winter a swell would push oil towards Kangaroo Island, the Spencer gulf, the Eyre peninsula and further east. Whatever the scenario, the modelling found there was a 70% to 80% chance of oil reaching the shoreline at levels of up to 424g per square metre.

BP has not released spill modelling but has said it would be able to plug any leak within 35 days, although Guardian Australia previously revealed this depends upon shipping and installing capping equipment from Singapore, 4,800km away, and a containment system from Houston, more than 14,000km away.

A federal government assessment has said this plan was “optimistic”. It took 87 days to stem the leak after the Deepwater Horizon disaster in the Gulf of Mexico, which killed 11 people and thousands of marine animals. Any recovery mission would have to deal with the Great Australian Bight’s strong winds and high seas; waves reach as high as 10 metres in winter.

BP hopes to open up a potentially lucrative new oil field with its exploratory drilling, which is earmarked for an area 395km west of Port Lincoln and 340km south-west of Ceduna. Each well will take between 45 and 170 days to drill. The first is planned for spring next year.

Environment groups are opposed to the drilling and claim it puts a pristine area of biodiversity at risk. The Great Australian Bight is a breeding and feeding ground for a large array of species, including blue whales, southern right whales, great white sharks, sea lions and various seabirds. Endangered loggerhead and leatherback sea turtles are also found in the area.

The Wilderness Society says an oil spill would threaten a $1.2bn tourism industry that relies upon the scenic South Australia coast, as well as the state’s $442m fishing industry. The losses to fishing and tourism would be multiplied if fisheries in the Bass Strait were shut down.

The oil spill modelling was conducted by an oceanographer, Laurent Lebreton, and was peer-reviewed by Matthias Tomczak, emeritus professor of oceanography at Flinders University. Lebreton analysed four key scenarios, based on the amount of oil spilled, whether BP could cap a spill in 35 days or not, and whether it occurred in summer or winter.

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“You take wind, ocean conditions; you look where oil particles are going and we tracked trajectories based on 20 years of data,” Lebreton said. “I don’t think our results would be much different [from BP’s].

“The Great Australian Bight is quite remote; the industry isn’t as well established as the Gulf of Mexico. We are looking to find solutions for global warming and yet we’re spending billions to drill deeper and deeper for oil. I’m sure there are a lot of brilliant people working at BP and I hope nothing goes wrong, but it’s a big risk. It’s just not worth it.”

BP said its modelling allowed it to plan for a “range of credible spill scenarios” and that it had commissioned the Australian Marine Oil Spill Centre to chart the southern coast and devise contingency plans.

A company spokeswoman said BP’s analysis showed that “in a worst-case scenario oil would take several weeks to reach shore and the direction in which it could drift varies due to seasonal differences in current and wind direction”.

“The environment plan contains an oil pollution emergency plan that details how in the unlikely event of a spill, BP will be able to stop it, recover oil and support rehabilitation.”

BP insists it would be able to halt an oil spill within 35 days by bringing in equipment from Singapore and Norway via Fremantle’s port. Offshore oil containment and protection booms would be available immediately from Adelaide, BP said.

Peter Owen, the Wilderness Society’s South Australia director, said: “An oil spill in the Great Australian Bight from a deep-sea well blowout would be a disaster for fisheries, tourism and marine life.

“The damage would be irreversible. We don’t need a Gulf of Mexico disaster in the Great Australian Bight.”

The National Offshore Petroleum Safety and Environmental Management Authority has 30 days to consider BP’s environmental plan. It may ask for more information and extend this process before approving or rejecting the plan.