Their boats were intercepted by the French navy off Belep last week and escorted to Noumea.
The captains were immediately tried and imprisoned while the 30 crew would be deported to Vietnam.
The boats were found to have beche-de-mer on board as well as shark fins, which are reportedly worth about $US700 a kilogramme.
Shark finning is prohibited in New Caledonia.
Earlier this year, New Caledonia and other areas in Melanesia were targetted by dozens of Vietnamese blue boats.
Photo: AFP A Vietnamese "blue boat".