Well I think the 50% applies and does not depending on circumstance. Ever watch charters flag a shaker around or a troller drag a fish around for hours? Many or most perish.

What I am familiar with is Chinook in transition waters in bays and rivers on the coast. 50% mortality would be good if you get them in the bay or bottom tide water and while many will proceed up river they fail to spawn. Bio once explained all biological reasons then said this. Chinook in transition ( females especially ) are coming from salt to fresh, temperatures and environment and it is stressful. Add to it in females they pulling energy from their bodies and putting it into egg development which makes them very vulnerable.

You hook them, fight them, and release them in some manner you wind the clock nature has on them down so far they can not get back the lost strength to spawn. Farther upstream you get them the less the impact and once they harden ( slime ) and are out of transition waters they can take the impacts of C&R with low losses.