They weren’t left with much of a choice. They would hail the illegal fishing boats and the boats would just book it back to international waters, wait for the Argentinian boats to leave then immediately go back and start fishing again. These fishing boats were turning off their transponders right before crossing into Argentinian waters, it’s isn’t like they didn’t know exactly what they were doing. If you continously knowingly and deliberately violate a countries borders then you should really expect to be shot at.