My good friends Kirk and Mandy, who I teach freediving with every now and again, did a top-secret project a few years ago, and yes, it was this film. If you don’t remember, it was the film about the cover in Japan where they capture dolphins for dolphin shows and slaughter the rest. It was produced by the Ocean Preservation Society, directed by Louis Psihoyos, and funded by Jim Clark (of Netscape fame).
You can find plenty of clips and trailers for the movie online. They needed Kirk and Mandy to (1)freedive with dolphins and whales and (2)set up some hydrophones at the bottom of the eponymous cove, and freediving was the quickest was to do it.