Moreover, I don't know if you have ever been deep-sea fishing, but when you pull a fish up from a hundred-plus yards underwater quickly, they tend to not survive if you do toss them back - quite often the pressure differential blows their lungs right out their mouths, and if not, they usually get scooped up by the blue sharks that also dog behind fishing boats.
I'm sure you know, but for the people down-voting you: You often have to kill dogfish when you pull them up because they have poisonous spines on them and you don't want to get pricked while they're thrashing around.
I've never done deep sea fishing, but when fishing with my grandpa he'd cut them up and use them as crab bait, which seemed like a good use for them to me.
Moreover, I don't know if you have ever been deep-sea fishing, but when you pull a fish up from a hundred-plus yards underwater quickly, they tend to not survive if you do toss them back - quite often the pressure differential blows their lungs right out their mouths, and if not, they usually get scooped up by the blue sharks that also dog behind fishing boats.