Because the females are the larger species since they have to carry their young. I suspect that the 15-16 footers were females. In any event you were lucky to see them this early. In fact your story suggests you saw far more than we did. Our oceans are changing-no doubt and the fact that there were other boats there simply confirms that. Years ago you would not have seen any boats there this early-let alone sharks. Do you recall what the water temperature was? Your right about their "presence". You don't see them "arriving". (LOL) Suddenly they are simply there ! Your also right about wanting to hog the cage. Me too. You were lucky to have three cages. Were there any non-divers on the trip who simply wanted the experience?