Sydney Fifty years ago, a Sydney Christmas involved midnight Mass, a roast turkey and maybe a swim at Bondi Beach. Today, the most important pilgrimage Sydneysiders make isn't to church, but to the fish market in Pyrmont. Indeed, Sydney's appetite for seafood is insatiable. Last year, the fish market, a squalid set of buildings next to a busy flyover, sold A$93 million (HK$623.5 million) worth of seafood. Things move into overdrive at Christmas. Last year, when the market stayed open for 36 hours on December 23-24, 80,000 people crowded into the markets to stock up on prawns, lobster, tuna, snapper and, most important of all, oysters. But the Christmas supply of the native Sydney rock oyster (grown all along the New South Wales coast) is being threatened by gangs of ruthless mollusc thieves, known in Australia as 'oyster rustlers'. Police estimate thieves made off with at least 55,000 oysters last year, and they expect the problem to escalate during the current harvesting season. Thefts usually occur at night, when the rustlers use boats to target remote oyster leases - well away from prying eyes. The stolen molluscs are then sold in pubs or at roadside stalls; some are apparently making their way on to Sydney restaurant tables. Growers say that over the past five years, oyster-rustling has escalated from small-scale pilfering to a major threat to the industry. Noel Baggaley, a grower from Brunswick Heads, estimates that he lost A$20,000 worth of oysters to thieves last year alone. 'It obviously puts a very sour taste in your mouth,' he said. To combat the rustlers, authorities have introduced a raft of new surveillance measures, including video cameras and laser beams for detection. In addition, oysters are being given 'microscopic signatures' that will allow them to be tracked wherever they go. Dots are sprayed on to the surface of the oysters, and each dot can be inscribed with the name of the oyster lease, the owner's name and other information. The technology was first developed during the second world war. Operation Trident, a joint initiative by the New South Wales police and the Department of Primary Industry, aims to identify the Mr Bigs of the illegal oyster trade - and prevent others from taking up the activity. 'The more [the crime is reported], the more we can build up an idea of where the hot spots are and which people might be involved,' said a police spokeswoman. In addition, police based in two of the major oyster-growing regions - Port Macquarie and Forster - are being trained to recognise stolen oysters and will crack down on illegal roadside vendors. Anyone caught selling stolen oysters can be fined up to A$275,000. The oyster industry says rustling also threatens the health of consumers, since stolen oysters may not have been purged of harmful bacteria and toxins. Sydney's gourmets have also thrown their weight behind the statewide crackdown on oyster rustling, appalled at the prospect of having to eat what they consider the far less attractive Pacific oyster. 'A fresh unwashed Sydney rock oyster is one of the smaller, more exquisite pleasures of living in the harbour city,' said restaurant critic Guy Griffin.