The methods of killing cephalopods for commercial fishing aren't exactly what I would consider humane. Generally they are asphyxiated, thrown into freezing brine, or simply clubbed to death. There is a also a process called "reversing the mantle" which I can't find much information on but it is reported to be one of the less humane ways and frankly just the name sounds pretty terrible. Ironically the most humane method, slicing the brain, is avoided because customers don't like blade marks specifically because they believe it indicates mistreatment.