The United Nations on Tuesday all but blocked caviar exports from countries producing the luxury food item until they provide more information about the sustainability of their sturgeon catch.

Many sturgeon species are suffering "serious population declines" and new quotas proposed by exporting countries may not fully reflect the stock reductions or make allowance for illegal fishing, said the U.N. Convention on International Trade in Endangered Species of Wild Fauna and Flora, or CITES.

"Countries wishing to export sturgeon products from shared stocks must demonstrate that their proposed catch and export quotas reflect current population trends and are sustainable," said Willem Wijnstekers, secretary-general of CITES, which regulates legal caviar exports through an international system of permits.

"Governments need to fully implement the measures that they have agreed to ensure that the exploitation of sturgeon stocks is commercially and environmentally sustainable over the long term," Wijnstekers added.

Information recently provided by sturgeon-exporting countries bordering the Caspian and Black seas, as well as the lower Danube and Heilongjiang-Amur rivers on the Chinese-Russian border, indicates that stocks are falling rapidly, CITES said in a statement.

Major caviar exporters include Russia, Kazakhstan, Azerbaijan and Iran.

The agency "remains hopeful" that the exporting countries will supply the missing data, which may allow international trade to resume.

But because the CITES system only allows sturgeon products to be exported during the year in which they are harvested, it is not possible to export caviar and other sturgeon products from shared stocks until the body approves new 2006 quotas.

CITES' 169 member countries have set strict conditions for permitting caviar exports. Countries sharing fishing grounds must agree among themselves on catch and export quotas based on scientific surveys of the stocks.

The Geneva-based U.N. body imposes annual quotas on caviar exports — some 250,000 pounds in 2004, down from about 320,000 pounds in 2003 — but environmentalists say that has not prevented the sturgeon's decline.

CITES halted most caviar trade from the Caspian Sea for one year starting in 2001, but allowed sales to resume the following year because of rising sturgeon stocks.

The conservation group World Wildlife Fund welcomed the CITES decision, noting that caviar importers such as the United States and European Union need to ensure the legality of the goods they bring in.

"Sturgeon have been in dire straits for some time and it has been clear that something drastic had to be done to stop the rampant trade in illegal caviar," WWF's Susan Lieberman said.