Over two weeks at sea, the scientists spotted pilot whales and spinner dolphins, orcas and more. But not a single sperm whale had crested the choppy waters of the western Indian Ocean.

Then, an underwater microphone picked up a series of unmistakable clicks and squeaks. A large pod of the endangered whales was nearby. And from the sound of it, they were feeding.

The scientists are on a monthlong quest to document whales and other marine mammals living around the Mascarene Plateau, hoping to bolster arguments for protecting the remote 2,000-kilometer underwater ridge to both fight climate change and protect ocean wildlife.