Shark fin soup is an ethical riddle wrapped inside a culinary enigma. The enigma is taste. Despite complex, week-long preparations - drying, soaking, paring, boiling, boiling, boiling - comparable to those for that extinct Victorian banquet staple, turtle soup, the fin tastes of exactly nothing. Or rather, it tastes of something stripped of its flavour. It also strips assets at £50 a bowl in swanky establishments.
Why bother? Hemlines rise with economic fortunes; in recession, skirts balloon. A similarly perverse logic dictates that the scarcer a food, the more we want it and the more we'll pay. In consequence, many shark species may disappear by 2020. Several hundred million years of adaptability and omnivory crowned the shark King of the Deep. Yet conservation campaigns flounder before those dead eyes, that fanged frown . . . Thanks to Jaws, the fin is a totem of terror - even if surfers, the most vulnerable human bait, are likelier to die of beestings. The creature with most to fear from shark's fin is the shark.
Until the mid-1980s the Chinese government derided shark's fin as an imperial delicacy, but as tiger economies roared, so did demand for the pedigree soup made from it. Classed as a "Pu" (strengthening) food, it is thought to soften ladies' skin but, like rhino horn, make men hard. Politicians and actors are devotees. (Consumption fell after WildAid blew the gaff on mercury levels. Mercury kills sperm.)
The emperor's soup is a gelatinous, chicken-stock gloop, so thick that it traps air. However fabulously silky, its chief virtue is its testimony to the chef's skill: alchemy that renders smelly cartilage an ethereally melting substance.
Ecology Letters estimates that 73 million sharks are slain each year. This figure is conservative: much trade is domestic or under-the-counter. It isn't merely an Asian issue. Spain leads global imports, and exports the product to Hong Kong. The market is finely calibrated. There's a whole world of difference between the rates for shark steak (£1 a pound at Billingsgate Market) and those for fins (up to $270). Hence "finning" prospers - a cruel practice in which sharks are scalped of their four (occasionally three) fins and dumped overboard. Sans fins they sink and drown. Business is booming but unsustainable. Ecological catastrophe spurs economic disaster. Sharks produce few young; many do not breed before the age of 15.
Of a random dozen Chinese restaurants in London, only one, Mr Wing, does not serve shark fin. Few would comment on how it's sourced. Apparently much of it comes in suitcases from China. The best-tasting rendition is Michael Peng's at Hunan, which operates an anti-finning policy.
It might make you live for ever. But chilli beef is tastier by far.