Using a model based on biodiversity indicators, scientists found the number of shark and rays inhabiting the open ocean across the globe has drastically fallen by more than 70 per cent in 50 years.

The clear driver of the "alarming" trend was a doubling of fishing pressure and a tripling of shark and ray catches, the team of researchers from universities around the world concluded.

"The numbers show the global abundance of oceanic sharks and rays has fallen to the point that 75 per cent of these species now qualify as threatened with extinction," said James Cook University's Dr Cassandra Rigby.

"The alarming trend is that there has been this decline, and that is even maybe more severe than we think because we only started looking at analysis about 1970.

"These open ocean fishing fleets have been expanding globally since before the 1950s."

Three of the 18 species examined by the team are critically endangered.

Despite poor outlooks for many other species, great white sharks and the great hammerhead shark populations in the Northwest Atlantic Ocean appeared to be recovering due to strict US laws now protecting them.

Similar protections, including science-based fishing limits, are urgently needed across to globe to prevent shark and ray population collapses, Dr Rigby says.

"I hope it is a call to action. We can't just sit back and do nothing."

The high number of shark attacks in Australia is not an indicator that populations are thriving, she says.

"We've got 1200 species of sharks and rays in the world and those responsible for attacks are just a couple of species."

Eight Australians were killed in shark attacks in 2020, the highest number since 1929.

The paper, published on Thursday, is part of the Global Shark Trends Project, which is reassessing the population of 1200 species around the world.

Australian Associated Press