They're hunting these whale looking things and when they kill them, they drill a hole up into their adrenal gland and fill up this giant vial with that they call liquid gold, which has anti-aging properties and "way way way more than you can get from a human being." (So....they usually get it from human beings?)
It's so valuable they don't even bother with the rest of the whale's body. They just take the adrenochrome and bounce.
On several occasions many references were dropped throughout the movie. The cloning or cross breeding was the first major indicator with the "incubators". The "whaling" scene was clearly telling the world what they're doing and the direction they are going. It was a dark place messaging movie.