Sting ray

Sting ray, originally uploaded by Ladymaggic.

I think this was caught by a fisherman and discarded.
It was lying on the shore

Steve Irwin was killed by a Sting ray. They are considered dangerous

Stingrays inhabit tropical to temperate water, from open sea to many kilometres upstream in brackish water. There are Whiprays, Giant Stingrays, Butterfly Rays, Eagle Rays, Round Stingrays, Cow-nose Rays, Mantas, Freshwater Stingrays and River Rays.

Stingrays are bottom dwellers, so that their flat body is often submerged in sand and only detectable by an eye or two, a piece of tail or the spiracles (water intakes) showing above the elevated disk or mud. Usually shallow water creatures they have been found in tropical waters at 30 to 60 meters. At up to 2 metres across and 4 metres long, a 2 ton ray is an impressive creature. Manta often jump out of the water and have occasionally damaged fishing boats. Stingrays feed on a variety of shellfish, molluscs, crustaceans and worms. The one or more spines are used for defence.
The stingray is non-aggressive, but is capable of protecting itself. Treading on the dorsal surface by mistake or swimming too close above a ray can result in a reflex upward and forward swing of the tail. The injuries can be either a sword like lacerations or penetrating injuries with the serrated spine. Serious injury can either be from the physical trauma of a vital body part, from the venom of the spine or both. In the USA 1,500 stingray injuries are reported annually.

http://www.nswseakayaker.asn.au/mag/47/stingrays.html