You have no sense of global economics. To sell to the international market, you need to have a cannery. To sell your catch to a cannery, you need to be able to deliver, on demand, hundreds of tonnes of tuna. That would take dozens of large fishing boats. None of this is going to happen in Manus for another few generations and by then the foreigners will have taken all our tuna anyway.
My advice is to let the Chinese and Philippinos continue to gain control of the PNG tuna resource.