Two whale sharks affectionately known as Stumpy and Zorro have been tracked by researchers making a feeding pilgrimage to Ningaloo Reef every year for more than two decades.

The scientists believe the endangered creatures are the longest-studied wild sharks in the world.

Murdoch University researcher Dr Brad Norman and Associate Professor David Morgan have been photographing Stumpy and Zorro at Ningaloo since 1994 - meaning the creatures have visited for at least 22 consecutive years.

Whale sharks are thought to live to about 80 years and are the largest known fish species.

Dr Norman said Stumpy and Zorro were some of biggest whale sharks in the area, and they had been able to prove the pair had visited Ningaloo annually to have a good feed.

Stumpy and Zorro are believed to be among the longest-studied individual fish on the planet. ( Supplied: Indian Ocean Imagery )

The creatures are easily identifiable by the shapes of their tail fins and scars.

"They are big boys ... and now we know they are mature. It's really interesting because most of the whale sharks we get coming back to Ningaloo are young males," Dr Norman said.

He estimated Stumpy and Zorro were at least 40 years old, and said they could continue visiting WA for another two decades.

"These two, they've been coming back for such a long time, and we've been able to see the progression through to maturity, we think these two big boys have been out there mating and might be the father of many."

Recording the whale sharks over such a long period has helped the researchers gather knowledge about the species' reproductive activity, which remains largely a mystery.

Stumpy and his fellow whale shark Zorro could continue to visit WA for another two decades, researchers say. ( Supplied: Indian Ocean Imagery )

Female whale sharks can give birth to litters of approximately 300 pups, however neither mating nor pupping of whale sharks has been observed.

"Our studies of Zorro and Stumpy are helping us to understand when whale sharks first mature and become reproductively active," Dr Norman said.

"Based on photographs ... paired external reproductive organs of whale sharks up to 60cm long, Zorro first reached maturity in 1998 and Stumpy in 2001."

Dr Norman's ongoing research work is using satellite tracking to see where the mature animals migrate, in an attempt to find out where breeding activities are occurring.

The research has been published in the scientific journal Frontiers in Ecology and the Environment.