Now, amid increasing international efforts to curb the decline, the federal government will today protect the species, found predominantly in the tropical waters of northern Australia, under national environment law.

Under the protections the giant ray will be listed as a migratory species, making it an offence to take, trade, keep, or move the species from Commonwealth waters. Fishers will now also have to report any interactions, as is now the case for other protected species, such as dugongs and whale sharks.

The Environment Minister, Tony Burke, said while Australian populations of giant manta rays were fairly secure, globally numbers had declined 30 per cent. It follows its listing as threatened under the international Convention on the Conservation of Migratory Species last year.

The International Union for the Conservation of Nature recently deemed the species as vulnerable to extinction due to overfishing.

An investigation late last year by the Shark Savers organisation of the US found the main cause of the manta ray's decline was rapidly increasing demand over the past decade from Chinese and other markets for gill rakers, thin filaments that rays use to filter food from water, which are dried and boiled as medicines.

The group's report found gill rakers were fetching $US251 ($242) a kilogram in Guangzhou, southern China, where 99 per cent of the world's product is sold. It said traders spruiked gill rakers as an immune system booster, while others claimed it could treat chickenpox and cancer.