Actually the cause has practical implications. If it turns out to be fish stock depletion, that could have a bearing on shark conservation efforts, since increasing predator numbers without increasing the prey base could have an impact on human attacks.
Some time back in an older thread on using shark nets to protect beaches, arguments were raised that the shark nets don't keep out all potentially dangerous sharks and do kill scads of creatures, sharks and otherwise. The argument was put forth that shark populations are so depleted that the nets are unnecessary (people argued about the definition of 'necessary,' of course). A counter argument was that if not for the nets, yes, shark populations might rebound to some extent, but that could in theory increase attacks. Which leads off into the 'how many sharks is a human life worth' debate, which seldom if ever leads to closure.
My point is, if it turns out attacks are on the rise, and that trend holds up over time, it would be useful to know what's causing it. But if you do a line graph following the incidence of rare events, the line will jump up and down, as even a couple of 'extra' shark attacks can create a short term peak in your data.
Richard.