Yep, Jap fishing boats carry radios and will report your position. Mods vary, but you'll also run into many neutral or generic fishing boats that won't report you. Just be careful for any fishing boats around Japan. Not to mention some of them carry large machine guns, although I've only seen it in TMO, not RSRD. I surfaced near one once, didn't see the gun and the dern thang almost sunk me before I got dived again.
Notice radio mast and sneaky gunner on deck.
