Undoubtedly something similar to our situation here off the coast of SoCal. When I first started diving these waters in the late 60s, sharks of several kinds abounded. Blue sharks were seen very frequently... often numbering in the dozens just on the way from one dive site to another on the boat. Today it is a very rare sighting. I think I've only seen one blue shark at the surface while on a dive boat. We stopped oiffering shark dives because a full dayt of chumming well offshore (5-13 miles) might yield a few small blues and a mako or two. Long liners and gillnetters got the majority of them and even though we've put bans on those activities in place off our coast, sharks recover slowly. Fortunately some species like soupfin (tope) sharks and angel sharks appear to be rebounding, possibly great whites too, but it is a slow process for sharks in general.