In the absence of specifics, I thought I might read up about stingrays. Anybody who's worked on a trawler or even just dropped a line in the sea knows that rays can be dangerous. (Certainly Irwin was well aware. He was filming a series on that very topic.) Torpedo rays, coffin fish and numbfish can give the unwary a serious electric shock. Something to remember for a long time. Stingrays, stingarees, some eagle rays and others are capable of delivering an equally nasty shock—with one or more barbed spines on the tail. One of these spines penetrated Irwin's heart and killed him.
Several species of stingrays grow to a huge size. The smooth stingray (Dasyatis brevicaudata) of southern Australia, South Africa and New Zealand may be over two metres across, four metres long and weigh up to 350 kilograms. The tropical pink whipray (Himantura fai) is less bulky but it still a bloody big animal. A bloody big wild animal.
A stingray spine is usually barbed or serrated along its upper surface, so it causes more damage than a simple penetrating wound. In many species the sting is enclosed in a sheath of skin containing venom glands. On contact, the serrations saw through the skin, releasing venom into the wound. They mean business.
Penetration of any part of the body trunk (chest, abdomen, groin or back) ... is a grave medical emergency, partly because of the inexorable necrotising action of any venom deposited on penetrated viscera or organs ...
Williamson et al.
Although stingrays aren't considered aggressive, there are several cases on record of divers being attacked while swimming over them. Whereas injuries from stingrays are not rare, deaths are. According to Williamson et al., fewer than twenty people have been killed by these extraordinary animals. (A researcher interviewed on ABC television tonight said he had tracked down records of thirty deaths attributable to stingrays.)
What amazes me is the sheer bad luck of the episode. That and the curiously apposite manner of Irwin's death. I couldn't really picture him dying from old age. He wasn't that sort of person.
Last, P.R. & Stevens, J.D. (1994). Sharks and rays of Australia. CSIRO.
Williamson, J.A., Fenner, P.J., Burnett, J.W. & Rifkin, J.F. (1996). Venomous and poisonous marine animals. UNSW Press.