I think every fisherman is going to kill the fish for money only. So, he is more busy in catching the fish, so any fisherman cannot say that he or she had killed the catch mercifully.
Actually, no one has suggested that they do it for profit. It seems that the majority are like me in catching what we can eat, not to sell to a market. There is no point of saving and freezing as it alters the taste. We catch and release or catch and eat, go use that argument on the trawlers and net boats. Sport fishermen are not providing tons to the market. There is a vast difference between sport fishing and commercial fishing.
Not sure what you fish for, but if you fish for tuna, mackerals, kingfish or other similar saltwater fish you definitely need to bleed them. Cut the gills and place them head down in ice will do it pretty quickly. Otherwise the meat will be tainted. We make sushi and sashimi right on the boat and I can tell you if you don't bleed them they will taste like crap...
As far as humane? I have caught large saltwater fish with massive hooks hanging our of their mouths and big shark bites in thier backs and they are eating like there is nothing wrong, so I don't really believe that they feel pain anyway. Either way, if I am going to keep them I kill them right away and get them on ice.
I like to use a sharp ice pick to the head right behind the eyes. Logically that is where most fish brains are located. A quick cleaning and into a ziplock bag into the ice chest. Never had a problem with fish taste, most bad flavors come from the internal organ contents seeping back into the meat. A good sharp knife and some precise cutting will go pretty far in preventing organ contents leaking onto the flesh.