As astute readers of my previous giant-squid posts will know, scientists have never observed one of these monsters alive. We only find them when they wash up dead on shores. In Spain, they normally only find one giant squid per year. But in the autumn of 2001, five suddenly washed up dead, and in 2003 another four were discovered. What happened to kill them all at once?

A marine expert in Spain thinks he knows the culprit: Oil companies. Angel Guerra of the Institute for Marine Investigations noticed that in those precise time periods, offshore oil companies were firing high-intensity sonar at the sea floor to try and find new oil reserves. Those sonar guns shoot utterly ferocious noise: 200-decibel pulses of 100-hertz sound, from an array of 10 guns. When scientists examined the dead giant squid, they found that none had external damage — so it was unlikely they’d been killed by another sea creature. But they did have extensive internal injuries, as the New Scientist reports:

In two squid the damage was extensive, with stomachs and hearts ripped open and muscles disintegrated. “Some organs were unrecognisable,” says Guerra.

And all the squid had badly damaged ears. Guerra thinks this might have disoriented the giant animals and made them swim to the surface, where they suffocated, as water temperatures there are too warm for the oxygen-carrying molecules in their blood to function. He suspects that in squid with massive internal damage, the blast caused dissolved gases in their tissues to form bubbles, such as those produced by shaking a fizzy drink.