Some of those pirates have RPGs. The twin Bofors on my father's old boat would have had the range but not the ability to depress if the pirates got through. Standard practice in those days, though, if a small boat came too close and ignored orders to move away, was to hurl a depth charge at it. Basically if you saw a fishing boat with a mysterious hump in the stern, and the crew suddenly rushed towards it, it was the Japanese and they were about to get their artillery going. You did not give them the chance.
The fishing industry didn't just tank; large fishing boats (including from the EU) came and removed all the fish. Basically the same strategy as Uber.