Trade in shark fins from Hong Kong to mainland China dropped by almost 90 per cent last year, a green group revealed.
Overall imports to Hong Kong fell 35 per cent compared with 2012, WWF-Hong Kong added.
The fall comes amid a crackdown by the central government on extravagance and corruption, and pressure by environmental groups to stamp out the trade.
The figures, drawn from government statistics, show a drop in re-export volumes of 17.5 per cent. This was driven by a 90 per cent drop in re-exports to mainland China from 1.2 million kilograms in 2012 to 113,973kg.
Mainland China, formerly Hong Kong's biggest re-export market, fell to fourth place last year after being overtaken by Vietnam for the first time since 2010.
"We were very surprised when we saw this figure as the mainland has traditionally been Hong Kong's biggest re-export market," said WWF-Hong Kong senior programme director Tracy Tsang Chui-chi.
"We do not rule out the possibility that the central government's anti-corruption measures could have played a role in the big drop in re-exports."
No explanation could be given as to why Vietnam, a country with no apparent shark fin consumption culture, could have surpassed mainland China as a re-export market.
Fin imports to Hong Kong dropped from 8,285 tonnes in 2012 to 5,412 tonnes, their lowest level in more than a decade, the group said.
WWF's Tsang said more transparency was needed to regulate the fin trade. This would include improving the city's harmonised code system to track shark fin products.
"The government should improve the existing codes, following the coding practice used for bluefin tuna, to allow for the identification of shark species that need to be tracked.
"Scientific identification, through DNA testing of randomly sampled shark fins, could also be deployed for verification purposes," Tsang said.
She called on the government to collect and release full statistics on the shark fin trade, including species, volume and country of origin.
Trade in eight shark species is now restricted under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
Ricky Leung Lak-kee, chairman of the Hong Kong Marine Products Association, said the local shark fin industry had been hit hard by the fall in demand in mainland China. The industry had suffered a 60 per cent decline in shark fin import prices and a roughly 20 to 30 per cent drop in business over the past year, he said.
Leung rejected suggestions that the local shark fin trade was hurting the environment. He said about two-thirds of Hong Kong imports were from blue sharks, which were not listed as an endangered species under CITES.
"The industry follows international law stipulated by CITES. There is a reason why it exists … I don't understand why green groups and the government keep discriminating against us."