Blacktip Sharks by Enric Sala

Enric Sala has spent much of his career looking for the ocean's "time machines" -- areas rich in biodiversity and largely unaffected by humans. In this recorded webcast, Sala, a National Geographic Ocean Fellow, takes the audience to the ocean's last wild places and tells us what scientists are trying to learn from them.

This picture, taken by Sala, shows a congregation of blacktip reef sharks in the lagoon of Millennium Atoll in the Southern Line Islands.