Death toll from oil spills may be underestimated

March 31, 2011

Photo copyright: L Bejder, MUCRU.

A new study has revealed that the number of animal deaths caused by oil spills may be up to 50 times higher than previously believed.

Murdoch University Research Fellow and co-author of the study, Dr Lars Bejder, is one of several researchers who argue that basing fatality figures on the number of recovered animal carcasses does not give a true death toll.

The research focused on the Deepwater Horizon spill which devastated the Gulf of Mexico in 2010, but the lessons learnt can be applied to similar disasters such as the Montara oil spill that occurred off the northern coast of Western Australia in 2009.

“The Deepwater Horizon oil spill was the largest in US history, however, the recorded impact on wildlife was relatively low, leading to suggestions that the environmental damage of the disaster was actually modest,” said Dr Bejder.

“This is because reports have implied that the number of carcasses recovered, 101, equals the number of animals killed by the spill.”

The team focused their research on 14 species of cetaceans, an order of mammals comprising of whales, dolphins and porpoises. The researchers looked at annual carcass recovery rates and annual mortality rates and estimated that only about 2 per cent of cetacean carcasses are ever recovered after their deaths. This shows that estimates of deaths based on carcass recovery alone are greatly underestimated.

The team argue that marine conditions in the Gulf of Mexico and the fact that many deaths will have occurred far from shore, mean recovered carcasses only account for a small proportion of deaths.

“The research highlights the uncertainty of the damage that the 2009 Montara oil spill might have caused to cetaceans in the Timor Sea,” Dr Bejder said.

“Specifically, this spill occurred 200 km off the northern coast of Western Australia – two to three times further offshore than the Deepwater Horizon incident.

In the case of the Montara spill, no cetacean carcasses were recovered after the spill, but given it happened so far offshore it is likely that deaths occurred but we did not recover the evidence of them.”

Lead author on the study, Dr Rob Williams from the University of British Columbia urged methodological development to develop appropriate multipliers so that we discover the true cost of the Deepwater Horizon spill.

“While we did not conduct a study to estimate the actual number of deaths from the oil spill, our research reveals that the reported figures are a grave underestimation,” Dr Williams said.

The study has been published in the journal Conservation Letters. Partners in the research are the University of British Columbia, Dalhousie University, Murdoch University, Cascadia Research Collective, New England Aquarium, Aberdeen University, Duke University and Provincetown Centre for Coastal Studies.

Lars Bejder is a member of Murdoch University Cetacean Research Unit.

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Murdoch University Cetacean Research Unit July 18, 2011

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