By Jonny Hogg
BBC News, Antananarivo
Marine noise has been known to disorientate whales in the past
A mission is under way to rescue more than 100 whales trapped in a bay in the north of Madagascar.
About 30 whales have already died and experts are being flown in from across the world.
The site is near an area where ExxonMobil is carrying out seismic surveys but the oil company has denied any link.
The first whale became stranded at the end of May and the first fatality was reported three days later.
The majority of the melon-headed whales swam through a narrow entrance into a bay where they have become trapped.
ExxonMobil had been carrying out seismic surveying in the area, although it says this began several days after the first whale washed ashore.
However, it told the BBC it had been using echo-sounding before this.
The company said it is confident it is not responsible, given that its operation was over 50km (31 miles) away from the Baie de Loza, where the whales have been washed up.
Despite this, it has halted its surveying programme until the issue has been resolved.
Meanwhile, a rescue effort involving local people and international conservation agencies is under way to save the remaining animals.