Sharks have more to fear from us

The sight of a shark's dorsal fin slicing through the water is guaranteed to set most human hearts thumping, thanks to a certain Spielberg movie and the fact that shark attacks are widely reported by the media. However, horrific incidents such as the recent one at Muriwai Beach in New Zealand are mercifully rare.

There are around 400 known species of shark, although new ones are still being described and (as we shall see) many others are threatened with extinction. They range in size from the gargantuan 12-metre-plus (plankton-feeding) whale shark (Rhincodon typus) to the diminutive dwarf lanternshark (Etmopterus perryi), a Caribbean species that's two orders of magnitude smaller at under 20 centimetres:

Extremes of shark: whale shark (left); dwarf lanternshark (right)

Only a handful of shark species are known have attacked humans, and when attacks do occur the unfortunate humans are rarely 'prey' so much as the victims of mistaken identity or exploratory biting. Most commonly implicated in attacks are the legendary great white, along with tiger, bull and oceanic whitetip sharks:

Killer sharks: (clockwise from top left) great white, tiger, oceanic whitetip, bull.

The world authority on shark attacks is the International Shark Attack File, compiled by the Florida Museum of Natural History. The ISAF recorded 80 'unprovoked' shark attacks worldwide in 2012, in line with the previous two years -- 78 in 2011 and 82 in 2010. Although the number of recorded attacks has grown steadily each decade since 1900, that's not unexpected given the increasing number of humans spending ever more time in shark habitat over the same period. Of the 80 attacks in 2012, seven were fatal (an 8.7% mortality rate), compared to 13 fatalities out of 2011's 78 attacks (a 16.7% mortality rate). For more on the types of human-shark interaction, and more statistics, check out research by Neff and Heuter, sponsored by the Save Our Seas Foundation.

When we look at the numbers of sharks killed by humans, we're in a completely different ball game. The latest research, published in the journal Marine Policy, comes up with the following staggering figures:

"The global catch and mortality of sharks from reported and unreported landings, discards, and shark finning are being estimated at 1.44 million metric tons for the year 2000, and at only slightly less in 2010 (1.41 million tons). Based on an analysis of average shark weights, this translates into a total annual mortality estimate of about 100 million sharks in 2000, and about 97 million sharks in 2010, with a total range of possible values between 63 and 273 million sharks per year."

The authors' estimated population exploitation rates of between 6.4% and 7.9% per year exceed the average rebound rate (estimated from life history information on 62 shark species) of 4.9% per year. Under such unsustainable attack, it's no wonder that, where data exists, shark populations are demonstrably suffering 'ongoing declines'. Since sharks are the top predators in many marine ecosystems, these declines could trigger cascading effects with serious consequences for marine biodiversity.

How can shark mortality be curbed? The single most effective strategy would be to reduce the demand for shark's fins in Chinese cuisine. For example, a 2006 study that factored in shark-finning data (from auctions in Hong Kong) came up with annual shark-catch estimates between three and four times those of the United Nations Food and Agriculture Organisation (FAO). Much shark-finning is carried out at sea, with the rest of the unfortunate animal discarded overboard, often alive -- which is why this data doesn't appear in FAO shark-catch figures.

Shark's fin soup: a major cause of shark mortality

And what of shark's fin soup? Far be it from westerners to pass judgement on a cultural tradition stretching back to Ming Dynasty (1388-1644) China (albeit mostly for emperors and rich folk), but shark's fin itself reportedly has little taste, the ingredient being valued mostly for its texture. Beneficial properties ascribed by Chinese medicine to the mostly cartilaginous material can be treated with more scepticism -- especially as shark fin often contains high levels of mercury and is regularly bleached using hydrogen peroxide before cooking.

So, around 80 people attacked a year, of whom 10 or so may die, versus around 100 million sharks killed annually, a significant proportion of which feed demand for a tasteless ingredient in a traditional elite recipe with questionable health benefits. Which has more to fear: humans or sharks?


Update (Monday 11 March)
The CITES meeting in Bangkok has voted to give added protection to five species of commercially exploited shark: oceanic whitetip, hammerhead (3 species) and porbeagle. Promotion to Appendix II regulates rather than bans the trade in these shark species, and the vote can still be overturned in a final session later this week.

Update (Thursday 14 March)
CITES has accepted the 11 March recommendations to list five shark species, despite challenges from Japan, Grenada and China.