The "necessity" of killing deep hooked fish is vastly exaggerated by crazed conk-em-all anglers who are desperate to justify their need to kill fish. "It'd do no good to put 'em back, they'd die anyway. . .

Blah, blah, the usual bull #### lines here.
If the fish is alive and able to swim under its own power, according the scientific studies on C&R, there is an extremely high probability it will survive. If C&R produced a significant death toll, there would be entire trout rivers here that would be completely devoid of fish because they have been 100% mandatory C&R for a decade or more. It's amazing how many "deep hooked" fish survive when chronic conk-o-maniac meat fisherman are prevented from using their own "judgment".
Grouse