Almost 100 million sharks are being killed each year, with fishing rates outstripping the ability of populations to recover, scientists have estimated.

Sharks need better protection to prevent possible extinction of many species within coming decades, the researchers warned ahead of latest global meeting to discuss the trade in threatened species.

The Convention on International Trade in Endangered Species (Cites) meeting, starting on Monday in Bangkok, will consider greater protection of vulnerable sharks, including porbeagles, oceanic whitetip and three types of hammerhead to prevent unsustainable international trade in them.

Sharks are targeted for their fins for use in shark fin soup, a delicacy in Asia.

But as they are slow-growing and slow to reproduce, they are vulnerable to overfishing. The researchers estimated that global reported catches, unreported landings, discards and sharks caught and thrown back after their fins were cut off – a process known as finning – added up to 97 million fish caught in 2010.

The figure is only slightly down on the estimated 100m caught in 2000, and could be anywhere between 63 million sharks and 273 million a year, the research by North American scientists published in the journal Marine Policy said.

It is estimated that between 6.4% and 7.9% of all sharks are being killed each year, above the level that many populations can cope with, leading to declines in a number of species.

Lead author Boris Worm, from Dalhousie University in Halifax, said: "Biologically, sharks simply can't keep up with the current rate of exploitation and demand.

"Protective measures must be scaled up significantly in order to avoid further depletion and the possible extinction of many sharks species in our lifetime."

Although some regions, including the European Union, have banned shark finning, commercial fisheries for fins, meat, liver oil, cartilage and other body parts is largely unregulated in much of the world, conservationists warn.

Under the proposals put forward for consideration by the Cites meeting, five shark species would be listed as Appendix II which would ensure that any international trade in them is sustainable and legal. A previous attempt to have the trade in some species of shark monitored and regulated under the Cites treaty narrowly failed, but conservation charity Pew Environment Group believes there is a great deal of momentum behind the latest bid.

Elizabeth Wilson, manager of global shark conservation at Pew, said the proposals had broad support across developed and developing countries and campaigners were hopeful that something positive could come from the meeting.

She said the study published today showed that people were killing an "enormous" number of sharks.

"We are now the predators. Humans have mounted an unrelenting assault on sharks, and their numbers are crashing throughout the world's oceans."

But she said: "A simple vote 'yes' to support their listing could turn things around for some of the world's most threatened shark species. Countries should seize this opportunity to protect these top predators from extinction."

The Cites meeting is also considering protection for manta rays, which are being fished for their gill plates that are sold in China as medicine claimed to treat a range of health complaints from asthma to chicken pox and even cancer.

The trade is on the increase, with Mozambique recording an 86% decline in sightings of the fish over the last eight years, Ms Wilson said.

But manta rays are very important in eco-tourism, providing a major draw for divers who will pay a lot to see them, she added, raising hopes countries will want to protect them.