The crew and the boats were detained last month after they were caught fishing illegally in Rennel and Bellona.
The Solomon Islands Broadcasting Corporation reported that the 40 pleaded guilty to entering the country illegally, but they told the chief Magistrate John Numapo, they did not realise they were breaking the law.
Last week, the boats' owners were fined $US1.59 million each.
The fisheries minister, John Maneniaru, said if the owners did not pay the boats would be destroyed.
Photo: AFP A Vietnamese "blue boat".