And if so, many would not have radio?
Tfor2,
You are right. I know from personal experience, that very few Vietnamese fishing boats have radios. They may have walkie-talkies for local communication with other boats and they all will have mobile phones, but those are no use 100 miles from shore.
During offshore seismic operations, we employ chase vessels to keep fishing boats out of the way. The chase vessels often have to close withing hailing distance.