Four bones have been found in total at The Spit, but forensic tests have confirmed that at least one is not human.

Spear fisherman Drew Valentine, a former Gold Coast lifeguard, found what he initially believed to be a whale bone in water near the northern wall of The Spit about 11am last Thursday.

Forensic experts confirmed on Wednesday that bone is a human femur (thigh bone).

Mr Valentine uncovered a second bone on the southern side of the seaway, only 300 metres from his first discovery, on Tuesday.

It was initially thought to be another human bone, but forensic tests have determined it was not.

Police divers returned to the seaway on Wednesday and found two more bones near the southern seawall, close to where the second, non-human bone was found.

The two bones would be sent to Brisbane's John Tonge Centre to determine whether the bones were human, said Senior Sergeant Lucas Young from the Gold Coast Water Police.

"It could be someone's scraps - you don't know, it could be a lamb shank bone," he said.

"We don't know, until they [forensic scientists] tell me."

Senior Sergeant Young said one bone appeared to be similar to the femur bone recovered by Mr Valentine.

"The other bone is a small bone, we can't distinguish what it is," he said.

Already families, of people who have gone missing in the area or have drowned in the seaway, have contacted police in the hope the discovery may provide them with answers.

Senior Sergeant Young said it was too early to says whose femur was discovered.

But he is hopeful investigators will be able to close a missing person's case as a result

"That is what we're always after," he told reporters.

"If we can give closure to some family that is exactly the result, even though it's tragic circumstances."

It is also unknown whether the femur is from a male or female, or how long the bone was in the water.

Senior Sergeant Young said it could also prompt a fresh investigation.

"One we know the age of the bone that opens or narrows our scope," he said.

Mr Valentine returned to the water on Wednesday to help police divers with their search.

He said he spotted the femur bone standing upright on the ocean floor on Thursday.

"I was in around 30 feet of water and just about on the last breath ready to come up and I just looked over and to the left of me there was a bone standing upright, vertically, by itself, in the sand," he said.

"It was one of those moments where a light was shining right on it ...

"I do feel like a bone collector."

Senior Sergeant Young said it was not unusual for debris to be uncovered on the ocean floor.

"You've got a north-to-south continental drift, you've also got big seas that push the current north, you've got tides that run at several knots in and out of the seaway everyday, so there's a lot of variables," he said.

"Sand movement, that can uncover or cover up objects including bones. Even some of the [ship] wrecks off the Gold Coast get uncovered after storms and then slowly get covered again."

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