Yes .. now that you mention it, it could save some fishermen I killed :rotfl:
Well, I usually use scope to rule surfaces out, but sometimes you can't. And to wait for 4 NB lines, if there is a chance that target is sub, is not good idea. So sometimes I shoot on what I think is sub, even if I know it could be fishing boat. On the other hand, it can also be surfaced sub, and then safety would mean lost shot.
Wire controls again helps a lot here. Submarine will evade. Even the dumbest oldest AI submarine will detect TIW and will drop some CM (very audible) and flank away (very audible too). Fishing boat will just sit there, so you can get a hunch a disarm the torpedo. Human opponent can play dumb here, but that could really show dumb.
On the other hand .. fishing boats are there to catch fish, right ?