The growing worldwide demand for the gill rakers of Manta rays to be used for medicinal purposes is threatening this species.

Each year large numbers of Manta birostris and M. alfredi, the world's biggest ray species with wingspans of up to eight metres, visit the Ningaloo marine reserve as part of seasonal migrations.

However, this popular specie that attract nearly 12,000 visitors to Ningaloo Marine Park each year are under serious threat of hitting the endangered list, according to a recent report , the Manta Ray of Hope: The Global Threat to Manta and Mobula Rays, which highlights the need for protection in Australia waters.

Mostly found at Western Australia's Ningaloo marine park, the report said that manta and mobula rays are also declining worldwide, particularly in India, Sri Lanka and Indonesia.

The worldwide decline in the manta and mobula species has been traced to overfishing due to increase in demand for their gill rakers . The gills of manta and mobula rays are dried and boiled for preparation as a health tonic that is purported to treat a wide range of ailments.

According to Frazer McGregor, who leads a research team from Murdoch University, said added to the increased demand for rakers is a lack of protection for the rays in Australian waters. The Murdoch University field station in Coral Bay has been the home to WA manta ray research for the past six years.

"While the rays aren't killed in our waters, they are sadly not protected from fishing beyond the bounds of Ningaloo Marine," McGregor said. "Once they leave the marine park, they are at risk of being targeted by fishermen, even in Australian waters, where they have no protection."

He added that the manta ray tourism, a $2million industry in Ningaloo and Coral Bay, needs more regulation.

"Even within its safe zones manta rays are facing increasing pressure from unregulated tourism. We've been trying to get a code of conduct introduced for the tourism industry so there are strict guidelines about how to behave when interacting with them, but the government just won't take the next step and implement formal legislated rules of interaction," McGregor said.

Professor Mike Bennett, a ray researcher from the University of Queensland, said the report raises important issues about manta rays worldwide.

"It shows that as shark numbers have declined through overfishing, pressure on rays has increased as fishermen look around for other things to catch," he said. "Manta ray fisheries are unlikely to be sustainable; they have very conservative life histories, reaching maturity at about 10 years of age and producing a single pup every two to three years."

According to Mr McGregor, because of this situation, the International Union for Conservation of Nature recently has updated the status of manta rays from threatened to vulnerable due to overfishing.

"This fact needs to be acknowledged by state and federal governments, and see them given appropriate Australian protection before the next listing updates their status as endangered," he said