Live bit offshore

I got a chance to venture offshore to one of the canyons, we had caught some live snappers to bring along for Tuna baits. One of the guys happened to drop several of the live baits overboard. Now this is my question, if this happened in 70' of water outside any inlet those fish would have disapeared in a flash, however being 80 miles offshore these fish hung together tighter than a clams a$$ and never went more than 5' from the boat. How do they know? Do they sense or feel the water depth from the surface and recognize where they are?? Any guesses or facts