The study was conducted in very clear Canadian lakes - all of which have large populations of predators. Every bed is surrounded by gobies and aggressive predator panfish. Therefore, when the guardian male is removed from the bed for even a very short time the predators rush in and decimate the fry.
In our area the practice of catch and immediate release probably has little effect on the fry. However, when the guardian male is caught and removed from the area, the fry are left exposed to predators and have little chance of survival. There is a valid argument for catch and immediate release of males during the spawn but the abundance of testosterone in the boat will win that battle.