The discovery of a two-metre shark tied up by its tail and drowned off the New South Wales central coast has horrified divers.

Disturbing images have been released by marine photographer Robbert Westerdyk, who found the dead mako shark on Saturday after it had been strung up by the tail.

The animal was tethered to a buoy within HMAS Adelaide's exclusion zone off Avoca and Terrigal beaches.

Describing the scene as barbaric, Mr Westerdyk says he cut the animal free and it sank to the bottom.

"Someone had actually tied its tail round and round this marker buoy," he said.

"Someone must've done it because there was also a big slice through its mid-sections.

"Whether or not the shark was totally dead at the time... it was a really ugly sight to see."

Dr David Powter, a senior environmental science lecturer at Newcastle University's Ourimbah campus, says it appears to be a deliberate act of cruelty.

"This is such a senseless act for such a beautiful creature and it would apply if it wasn't a shark, if it wasn't a marine organism," he said.

"It's just such a senseless act to take a life like that for no purpose."

Dr Powter says mako sharks are sought by recreational and game fishers because they "put up a fight".

"It's a bit disappointing that if the animal is caught, then it'd be wasted effectively by being tossed back," he said.

NSW Fisheries is investigating the incident.