Sinking Fishing Boats - Bad Form?

[Catfish]

Hello,
historically speaking it was just not done. The fish being caught by french trawlers was bought and paid for (if most probably in occupation money) by the german Kriegsmarine, who after all needed to eat. There is even a story where a boat bought fresh fish from a british trawler. The fishing fleets remained relatively unharmed, even if some of them may indeed have sent a report to Great Britain if they saw a U-boat.
There were enough atrocities towards civilians, but probably not against fishermen.
Some british and formerly danish fishing boats got bigger engines and were used as blockade breakers to support the nowegian and french resistance, but were seldomly caught - and not by U-boats.
From the capitalistic approach a torpedo was probably more worth than a small fishing boat
As well U-boats sometimes used fishing fleets to cover ...
I would evade them for not alarming the bad guys.

Greetings,
Catfish