Name the specific place(s). I suspect in some cases, like my ridiculous example of body boarding off Seal Island near South Africa where the great whites hunt seals and breach attacking decoys, it's common sense applied to a very localized area, rather than waiting for the fatality rate to hit a specific number per sea-using population ratio for a given area.
And relatively small, isolated areas can be pretty easily avoided once known. That scenario is not to be generalized to very large regions of coastline.
Richard.