Letter from Moscow : Snaking north through the Caucasus mountains, skirting the rebellious province of Chechnya, the Makhachkala-Moscow train crosses some treacherous territory.
Federal guards manning checkpoints between the small, restive republics of southern Russia often report finding firearms and explosives on trains plying this route, and usually claim to have thwarted an attack by Chechen rebels further up the line towards Moscow.
One recent discovery represented a less deadly challenge to state authority than guns or grenades, but provided a glimpse of a thriving sector of the nation's black economy that robs the government of hundreds of millions of dollars each year, and is driving to the brink of extinction an ancient creature famed for its eggs.
Police searching the restaurant car of the Makhachkala-Moscow train last week caught the chef with some 130 kilos of illegally caught sturgeon, Ria news agency reported. He was heading to the nation's capital to sell the fish, whose roe are harvested and sold as caviar to those able to afford its salty luxury.
A few hours earlier, the chef's train had pulled out from the capital of Dagestan, a crime-riddled republic by the Caspian Sea, from whose waters some 90 per cent of the world's sturgeon is pulled.
But while the Caspian still has a near-monopoly on the world sturgeon's stocks, the size of that catch has plummeted over the last 25 years, according to the Convention on International Trade in Endangered Species (CITES), a United Nations body that has called caviar-producing sturgeon "one of the most valuable wildlife resources anywhere in the world today". CITES says the countries that fish the Caspian now take only a tenth of the sturgeon they did in the late 1970s, because of "reduced river flow, destruction of spawning sites, corruption, poaching, organised crime and illicit trade". The organisation says the illegal catch in the four Soviet republics that fish the Caspian - Russia, Azerbaijan, Turkmenistan and Kazakhstan - is more than 10 times larger than the legal take.
"The legal caviar trade is estimated to be worth some $100 million annually," CITES says. "Because prices of illegal caviar vary widely from country to country, it is difficult to estimate the value of illegal trade, but it is clearly enormous."
Because local efforts to stop the poaching have had little effect - due to the brutality and influence of the crime groups running the trade and the inability of the Caspian's littoral states to police its waters - international conservation groups have had to focus on stopping black-market caviar reaching consumers abroad.
Since 1998, all sturgeon and caviar sold on the world market has been obliged to carry a CITES certificate proving that is was caught legally and in line with annual quotas worked out between the four ex-Soviet states and Iran, the country with the Caspian's best regulated sturgeon-fishing industry. In light of dwindling stocks, the quotas have been practically frozen for the last two years.
But a lucrative black market still flourishes, feeding Russia's demand for the delicacy beloved of the tsars and now the nation's nouveau riche, and finding outlets to a hungry Western market where the eggs of the prized beluga sturgeon can fetch more than $3,000 a kilo.
The beluga can live for 150 years and grow to some 19 feet in length, but rapacious fishing means that very few now grow to full size, and many do not even survive the 12 or so years they take to reach sexual maturity and produce roe.
In 2001, the UN banned trade in beluga meat and caviar for eight months, while the ex-Soviet Caspian states drew up new anti-poaching legislation.
Now environmental groups want the UN to ban all trade in beluga caviar, but no decision can be made until the 2004 conference of CITES member-states.
US groups SeaWeb and the Wildlife Conservation Society are lobbying Washington to declare the beluga an endangered species, a move which would outlaw beluga caviar sales in the United States, where 80 per cent of annual legal production is consumed.
On Sunday, a senior law enforcement official in the once sturgeon-rich Volga region delivered a gloomy prognosis for the area's fishing industry.
"Since the 1980s, the annual commercial catch of sturgeon has shrunk from 28,000 tonnes to 337 tonnes in 2000," Volga Deputy Prosecutor-General Mr Sergei Gerasimov told Interfax news agency.
"If the fish resources continue decreasing at the current rate, the commercial fishing of sturgeon will have to be stopped." Conservationists also urge law enforcement agencies to punish seriously those involved in the illegal trade in sturgeon and caviar.
The police sent a crime report to the superiors of the chef on the Makhachkala-Moscow train, Ria reported. The 130 kilos of sturgeon were sent straight to the nearest smokehouse.