A conservation victory restricting global trade in more shark species will take a fresh bite at Hong Kong's market in fins, which has already been hit hard by persistent attacks from anti-fin campaigners.

Defiant fin merchants insisted the impact of the restrictions would be minimal as they would continue to import other species not covered by the Convention on International Trade in Endangered Species (CITES) agreement.

And a local anti-fin lobby group warned the measures, which aim to protect the oceanic whitetip shark, the porbeagle and three types of hammerhead, would be hard to enforce.

But traders in the southern Chinese city, one of the world's biggest markets for shark fins, which are used to make an expensive gelatinous soup, have already suffered from successful environmental campaigning.

New figures show shark fin imports dropped off dramatically last year to 3,351 tonnes from 10,340 tonnes in 2011, after some prominent Hong Kong hotels and restaurants struck it from their menus.

Hong Kong has traditionally handled around half of all global trade, exporting most fins to mainland China where they are considered a rare delicacy.

On "Dried Seafood Street", a pungent thoroughfare at the centre of the city's shark fin trade, dozens of shops show off their goods, from lower-quality fins wrapped in plastic to the premium variety displayed behind glass that fetch up to HK$10,000 ($1,300) per kilogram (two pounds).

"More and more young people think having shark fin soup is cruel," trader Frederick Yu said.

"For Chinese, the only two delicacies we have are abalone and shark fins. The Westerners eat caviar and foie gras, is that not cruel? Why do they stop us from eating shark fins?"

But Yu, who has been in the business for over 10 years, said he supported the sustainability of shark populations, adding that environmentalists were unfair to target traders.

Despite opposition from China and Japan, the 178-member CITES conference in Bangkok approved a deal that requires countries to issue export permits to ensure the sustainability of the sharks in the wild, otherwise they could face sanctions.

But Ho Siu-chai, the chairman of the Hong Kong Shark Fin Trade Merchants Association said the restrictions would only affect one-tenth of current business.

"It's not an issue for us -- we have about 400 shark species, we can always import other species," he told AFP.

"We see it positively. We don't oppose the new restrictions."

Humans kill about 100 million sharks each year, mostly for their fins, according to the UN Food and Agriculture Organisation (FAO), which says 90 percent of the marine predators have disappeared over the past 100 years.

The brutality of the practice sees fishermen slice off the fins before throwing sharks back in the water to die, campaigners say.

Hong Kong director for US-based Shark Savers, Silvy Pun, said while the three species already under CITES protection -- the great white, whale shark and basking shark -- are larger in size and more easily identified, the newly-listed species were hard to differentiate.

"The next step for Hong Kong will be very, very challenging," she said.

"The only way you can identify them correctly is DNA identification but as far as I know, this is not very well-developed yet (in Hong Kong)."

The government's conservation department said it would abide by the CITES restrictions, which must be introduced within 18 months, but would not elaborate on how it was planning to step up enforcement.

In the face of public distaste, some traders have stopped drying fins in the open on the pavement, moving them instead to rooftop locations.

And Pun was hopeful that the tide is turning.

"Hong Kong as a shark capital has the responsibility to conserve the shark population. Now we can take bigger steps to conserve sharks -- we can start and we can change," she said.