A TIP off has launched a police man hunt for the gunshot killer of a 5.2m king crocodile in the Fitzroy River.

An autopsy on the slaughtered reptile is under way after he was discovered with an apparent bullet wound to the head at an Alligator Creek location near Etna Creek yesterday afternoon.

Rockhampton Criminal Investigation Bureau officer-in-charge Detective Senior Sergeant Luke Peachey said the EHP contacted police who are now working with the environmental agency to track down who's responsible.

Police have released this image of the 5.2m crocodile shot in the head in the Fitzroy River.

Snr Sgt Peachey said it was the first crocodile murder he has investigated in his career, and was concerned that someone had "taken matters into their own hands".

He said a thorough investigation hoped to bring the killer to justice under the Animal Cruelty Act, and the culprit could face up to three years imprisonment.

Crocodile shooting update: Acting Inspector Luke Peachey updates the media on the 5.2M crocodile which was shot near Alligator Creek north of Rockhampton.

He said a first look at the animal suggested it had suffered a gunshot wound to the head, but no cartridges had yet been extracted.

Snr Sgt Peachey speculated given its size the prehistoric creature was quite old, and said environmental officers had suggested he would have been very territorial.

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"It's obviously a large male and we have been speaking with officers with a little bit more knowledge than myself, we'd believe that would be a very territorial male," he said.

"It's obviously very concerning this male crocodile... would appear to be shot.

"If someone has concerns about that crocodile being in that river obviously there are better agencies and the right methods to go about getting that crocodile removed rather than taking matters into their own hands."

EHP Conservation and Biodiversity Operations director Michael Joyce today said the dominant crocodile's death would impact the balance of the crocodile population in the Fitzroy.

Mr Joyce warned of increased aggressive activity by younger male crocodiles competing for the now vacant position.

"I cannot stress strongly enough the need for all river users to be aware of the risks and to be Crocwise," he said.

Mr Joyce issued an urgent message to everyone in Rockhampton the area is to be extremely careful and to report all crocodile sightings as soon as possible on 1300 130 372.

As part of police investigations, Snr Sgt Peachey said they would be talking to landholders, people who frequent the Fitzroy and anyone who may have information on the cause of death.

He could not confirm whether the croc's attacker struck from a boat or on a bank.

Detective Senior Sergeant Luke Peachey updates the media on the shooting death of a 5.2m crocodile near Rockhampton. Chris Ison ROK220917cpolice2

Snr Sgt Peachey urged they contact either Rockahmpton CIB or Crime Stoppers on 1800 333 000.

The shooting death comes as EHP officers are working to remove a big crocodile from the Fitzroy, after a reported sighting 4km upstream of the Barrage on August 3.

Under the current Queensland Crocodile Management Plan (QCMP) any crocodile greater than two metres in length or displaying aggressive behaviour in the Rockhampton Targeted Management Zone (Zone C) is automatically targeted for removal.

This includes the area from the Barrage upstream to Long Island.

A crocodile trap has been laid in the Fitzroy River after a beast measuring more than 2m was spotted near the Barrage. Chris Ison ROK151216ccroc2

Wildlife officers have been monitoring the area and confirmed the presence of a crocodile, greater than two metres in length, approximately three kilometres upstream of Pink Lily Sands.

A floating trap has been deployed in the area and members of the public are asked to avoid the area if possible while the removal operation continues.

It is an offence to interfere with a crocodile trap, including: