If Free Willy is any indication they waited until an Orca jumped above them and quickly attached a camera to its belly. To make my comment more productive, may

If Free Willy is any indication they waited until an Orca jumped above them and quickly attached a camera to its belly. To make my comment more productive, maybe they attach it to the fins using sticks and bait, like with sharks: https://phys.org/news/2016-06-camera-tag-white-sharks.html https://phys.org/news/2016-06-camera-tag-white-sharks.html