Between 63 and 273 Million Sharks Are Killed Worldwide Each Year

A flood of conservation research has come to the fore recently, in preparation for the first conference in three years of the Convention on International Trade in Endangered Species (Cites) member parties. A new shark study is a big deal: In probably the best survey to date on the mortality rates of sharks globally, a group of North American researchers estimate that between 63 million and 273 million sharks are killed every year, with the likely number around 100 million.

There are two important things to note here: First, the survey, published in Marine Policy, covers all forms of shark mortality, be it legitimate fishing, shark finning, or sharks caught and discarded for various reasons. Second, and more importantly, are these levels sustainable?

The study looked at a trio of estimates for sharks' exploitation rate–the amount of sharks caught each year–which ranged from 6.4 to 7.9 percent of all sharks each year. According to David Shiffman at Southern Fried Science, who's an excellent shark resource, the average rebound rate–how much yearly growth there is–is estimated to be around 4.9 percent. While both rates vary for different species, he said around two-third of all known shark species are being fished faster than they can recover.

"Biologically, sharks simply can't keep up with the current rate of exploitation and demand," lead author Boris Worm, of Dalhousie University in Halifax, told the Guardian. "Protective measures must be scaled up significantly in order to avoid further depletion and the possible extinction of many sharks species in our lifetime."

A disappointing aspect of the study was that fishing rates haven't declined appreciably since a previous survey in 2000, despite increased awareness and regulation protecting sharks. With the Cites CoP meeting starting tomorrow, there's hope that new regulation can be ratified to help make sure that the shark trade is sustainable.

“[The study] shows that the problem of unsustainable shark fishing has not been solved by existing regulations, and that a majority of shark species are threatened by overfishing," Worm told Shiffman. "CITES is an effective tool in preventing extinction of some of the most vulnerable species. On land, CITES has been 100% effective in preventing extinction of thousands of listed species. I hope this can be applied effectively to ocean creatures as well.”

Five species of shark, including a trio of hammerheads, are currently proposed for listing under Cites Appendix II protections, which would guarantee that internation fishing is legal and sustainable for those species. That sustainable part is key, as it legally requires fisheries to show that their catch of these non-endangered species isn't threatening population levels. That's a big potential step, as currently only three species of shark are listed in Cites appendices, and as many sharks worldwide are threatened by the rapid degradation of coral reefs. It's not yet a given that the proposal will be ratified, but it's a good possibility. I'll update when we know more.

@derektmead