Last week, the French navy intercepted two blue boats off Belep and found that they had beche-de-mer on board.
Now television reports say shark fins, which are reportedly worth about $US 700 a kilogramme, have also been found on the vessels.
Shark finning is prohibited in New Caledonia.
The French High Commission says the boats and their 30 crew are being towed to Noumea.
Earlier this year there were multiple arrests in New Caledonia where French naval surveillance spotted dozens of boats in operation.
Several Vietnamese captains caught in New Caledonia are serving jail sentences while a large number of sailors have been deported.
Earlier this year, the Forum Fisheries Agency said the Vietnamese blue boats should be labelled reef robbers for their persistent illegal activities around Melanesian islands.
Photo: RNZI/Supplied by Frank Aote’e