Gourmets are facing a shortage of caviar because of aggressive fishing by Russian and Iranian trawlers.

Even if the expensive delicacy is found, it may not be genuine caviar, which is the unfertilized eggs of sturgeon. Rather, conservationists warned, it might just be ordinary fish eggs labeled as caviar.

The best Beluga caviar from Russia costs more than $80 an ounce in American gourmet shops. Other caviar can sell for as little as $10 an ounce. Last year, nearly $12 million worth of caviar was brought into the United States, but mark-ups made the value of retail sales nearly three times that much. Total world trade was about $125 million, according to a World Wildlife Fund report.

“After a while, there just won’t be any more of those sturgeons,” said Andrea Gaski, director of the fund’s wildlife monitoring program. “We can’t know just when.”

Caviar can be obtained only by killing the female sturgeon while she is carrying the unfertilized eggs. The killing of other sturgeons is depleting the source of the mature, egg-bearing females.