Soviet whalers wiped out blue whales from part of the Indian Ocean 50 years ago. Underwater audio reveals the gentle giants have returned.

• Blue whales near the Seychelles were wiped out half a century ago by whaling.
• After sightings, scientists set up audio recording devices on the seafloor near the island nation.
• They found blue whales had returned to the area, and think the whales may be using it for breeding.

A population of blue whales near the Seychelles islands in the Indian Ocean that was wiped out half a century ago has returned after the area was protected, according to a new study.