A GIANT squid, one of the most mysterious and least understood of marine creatures, has been found floating off the New South Wales south coast.

The Daily Telegraph fishing columnist Al McGlashan discovered the remains of the ocean titan - so fresh it still carried its ruby red colouring - about 50km off Jervis Bay.

The carcass of the giant measured about 3m long, even though most of its tentacles had been bitten off, possibly in a fight to the death with its only known predator, a sperm whale, hundreds of metres below the surface.

"It must have died not that long before we found it because it didn't smell at all and its colours were still strong - most giant squid remains are smelly and rotten and just off-white by the time someone finds them," Mr McGlashan said.

Australian Museum squid specialist Mandy Reid said they can grow to 13m. Coincidentally the museum starts its Deep Oceans exhibition featuring a 5m model of a giant squid on June 16.

Dr Reid said the squid had either encountered a sperm whale or had come to the end of its short life and floated to the surface.

"Most squid only live for a year, they grow extremely quickly, but there is also a chance that it has been attacked by a sperm whale," Dr Reid said.

"Sperm whales are far bigger, heavier and faster in the water - the giant squid are quite slow - so the whale generally wins."

And finding a giant squid, no matter how fresh, does not mean a calamari feast will follow.

"They taste really bad, the flesh has an intense ammonia smell," Dr Reid said. "Ammonia makes the squid less dense than seawater, giving it neutral buoyancy so it doesn't waste energy constantly swimming."

Giant squid may taste appalling to humans, but are a treat for sharks.

As Mr McGlashan filmed the monster from the deep on Friday, a 2.5m blue shark - a slender, open ocean shark known for its intense neon blue colour and long pectoral fins - appeared and could not resist the free feed.

"It hoed into the squid straight away and didn't care a bit that it was right next to us; it was taking great chunks out of the squid in one bite," Mr McGlashan said.

"It goes to show not much goes to waste in the natural world. Everything gets recycled somehow."

Read Al McGlashan's Gone Fishing column every Friday in Sydney's best-read newspaper.