Fish that are held out of water for more than a minute have a 72% mortality rate. The ones held out of water for 30 seconds have a 38% mortality rate, and those that are released without being removed from water have a 12% mortality rate. This shows that the longer fish stays out of the water, the higher the chances of dying after release.  Many factors work together, from injuries gotten from the hooks to lack of oxygen and even shock and psychological torture that the fish goes through. This fish may die from all those factors, or they may be killed by a predator whom it could not run away from.