A dead sperm whale in the Gulf of Mexico

A dead sperm whale in the Gulf of Mexico Photo: Greenpeace

A CACHE of newly uncovered documents from the 2010 BP oil spill in the Gulf of Mexico - including gruesome photographs of a dead whale - are raising questions about the environmental cost of the disaster and the compensation the oil company will have to pay to set it right.

Documents obtained by Greenpeace under freedom of information provisions show Obama administration officials tightly controlling information about whales and other wildlife caught up in the disaster.

Their plight, especially endangered species such as sea turtles and sperm whales, has enormous financial implications for BP. The oil company asked a judge in New Orleans this week to finalise its $US7.8 billion ($A7.5 billion) settlement for economic damages arising from the spill. But BP still faces claims from the US federal government for environmental damage.

That looming legal struggle was apparently already on the minds of officials at the National Oceanic and Atmospheric Administration when crew aboard the research vessel Pisces spotted a dead sperm whale in mid-June 2010. The discovery was the first confirmed sighting of a dead whale since the blowout on the Deepwater Horizon drilling rig that April.

Observers on another vessel at the well site in June spotted five whales, including a juvenile, covered in oil.

The discovery of the whale carcass set off a flurry of emails - with repeated instructions from officials to crew aboard the Pisces not to release information or photographs.

The NOAA did put out a press release about the dead whale. But it was edited in a way which appeared to minimise the effects of oil on whales.

Scientists concede little is known about how whales respond to oil spills. ''We do know that oil spills do kill whales but we know very little about how lethal they are and what makes them lethal,'' said Hal Whitehead, cetacean research biologist at Dalhousie University in Nova Scotia.

GUARDIAN