I dont believe that report, quite frankly. Maybe an isolated incident, but I dont believe its happening as stated here.
Stingrays Found Mutilated After Irwin's Fatal Sting:
http://www.kcra.com/news/9825184/detail.html
Just MSM hysteria-mongering.
Injured stingrays no doubt turn up on beaches every so often in the ordinary course of nature. Until now, nobody would have thought to attach any significance to it.