Sydney: Australian authorities seized two Vietnamese fishing vessels and detained 30 crew members for allegedly fishing illegally in the country's waters. The vessels, apprehended in an Australian marine reserve 600 km northeast of Cairns in Queensland State are now being escorted back to the Australian mainland for further investigation, the Australian Border Force (ABF) said on Saturday. Authorities apprehended the vessels on Thursday after they were spotted by surveillance aircraft, the statement said. The ABF alleged the vessels contained diving gear to support 10 divers in the water at once, and contained six tonnes of sea cucumber believed to have been caught illegally. The Australian authorities said the apprehension of foreign fishing vessels operating illegally in Australian waters is paramount for the sustainability and economic health of the nation's fishing resources. "Australia's fisheries are some of the best managed in the world and as such they are the target of illegal fishers," Australian Fisheries Management Authority (AFMA) general manager for fisheries operations Peter Venslovas said. The apprehension follows two other fishing vessels being seized in April, one in the Torres Strait suspected of fishing for sea cucumber, and another in Western Australia state suspected of fishing for shark fin. Last month four Indonesian sailors were convicted for illegally fishing for shark fin in Australian waters. The fishermen were fined 19,200 Australian dollars ($14,131) and their vessel was destroyed.