Chinese couples who have chosen Friday – 11/11/11 – one of the most auspicious days of the year to exchange their wedding vows, could be among the last to mark the occasion by feasting on shark fin soup, if environmental groups get their way.

As the wedding parties scoop pieces of the slippery, glutinous flesh from bowls of broth, they will not just be respecting tradition; they will also be defying a growing campaign to ban the trade in shark fin that has now spread to its most lucrative market, Hong Kong.

It is easy to see during a short walk through Sheung Wan, a Hong Kong neighbourhood specialising in dried seafood, why the campaign to ban the trade worldwide has set its sights on the city.

Shark fins fill shop windows, ready to be hydrated and boiled before being added to a rich broth, a gastronomic preserve of wealthy Chinese since the Song Dynasty in the 10th century.

Rising prosperity since the 1970s has made the delicacy affordable to the middle classes, first in Hong Kong and now on the mainland. Eating it is so closely associated with new wealth that to say someone is "eating shark fin with rice" is to refer to their prosperity.

Hong Kong handles as much as 80% of the global trade in shark fins, bringing in catches from more than 100 countries, with Spain by far its biggest supplier.

In 2006 it took delivery of more than 10,000 tonnes worth $276m (£173m), according to the UN food and agricultural organisation. Most is consumed in Hong Kong and Taiwan, but also in mainland provinces such as Guangdong.

Campaigners say it is next to impossible to verify the fins' provenance, as they are dried and bleached, and often treated with ammonia, before reaching Hong Kong.

"The catches are not tracked at all, and there is no species monitoring or labelling," says Stanley Shea, a campaigner with the marine environment group Bloom Association, which last year conducted the most comprehensive survey to date of shark fin consumption in Hong Kong.

"We don't even know how much of it is eaten here or ends up in mainland China."

Many shark populations have plummeted by 90% in recent decades, according to campaigners, who warn that if over-fishing continues at the current rate, the most commonly targeted species will be extinct in a few years.

DNA analysis showed that 40% of shark fin auctioned in Hong Kong comes from 14 species, all of which appear on the International Union for the Conservation of Nature's "red list" of endangered species.

After years of fierce opposition from traders and retailers, campaigners in Hong Kong say the local population is finally waking up to the ecological catastrophe.

Several hotels offer discounts, cheaper room rates and other incentives for couples that choose not to serve shark fin at their wedding celebrations.

One online campaign calls on wedding guests to reduce cash gifts by about a third for couples who select the dish.

Last year campaigners persuaded Citibank Hong Kong to withdraw a promotion offering new credit card holders discount on a shark fin dinner.

On the mainland Yao Ming, the Chinese NBA star, has appeared in a well-received campaign to end finning, the practice of removing a shark's highly valued fins and dumping what is left into the sea.

But there are pockets of resistance, particularly among older people, who still regard eating shark fin as a means of expressing their Chinese identity.

"At weddings you have different people sitting around the same table," says Shea. "Young people understand the problem and want to do something about it, but at some point their parents stop them."

The manager of one Sheung Wan wholesaler, who asked not to be named, said traders were beginning to feel the impact of the environmental campaign.

"Sales are dropping and I think that is down to the campaign," he said. The manager's firm sells between three and four tonnes of shark fin a month.

"The wholesale price has dropped by about 20% over the past two months, although there are always fluctuations so it's too early to tell if this is a lasting trend."

Charlie Lim, a shark fin trader, is receptive to the message on sustainable fishing but accuses some campaigners of hypocrisy.

"The Chinese tradition of eating shark fin will be maintained, but will increasingly come from sustainable fisheries," says Lim, a prominent member of Hong Kong's marine products association.

"Chinese people and traditions do make an easy and readily identifiable target for largely western campaigners.

"But many western campaigners who are seriously interested in promoting the sustainable use of sharks should look more closely at their home fisheries and the 'boneless' fish products that their children may be eating from the supermarket."

Despite its early successes, the campaign has yet to challenge shark fin's place at the heart of Cantonese cuisine.

Bloom's 2010 survey revealed that 89% of the territory's 7 million people had eaten the dish at least once in the past year, with more than half saying they did so to observe tradition. Another poll found that only 5% of couples had opted for shark-free wedding banquets.

But 66% said they were uncomfortable with the idea of eating an endangered species, and more than three-quarters said they would not mind if it was removed from banquet menus.

Shea believes Hong Kong will be viewed as a pariah as long as it fails to introduce measures to protect shark populations similar to those introduced elsewhere.

"Hong Kong has always been a role model for the rest of China, and this issue should be no different," he says.

"Our message is that eating shark fin is unsustainable. At some point, the market is going to crash."