Monster,
Someone, on a different thread, pointed out that groundfish caught at depth and brought to the surface stand a very good chance of suffering fatal injury from over-expansion of their gas bladder (aka swim bladder):
http://en.wikipedia.org/wiki/Gas_bladder
You've no doubt seen extreme examples of this, in which the bladder distends out the creature's maw ... typically in fish caught roughly 100 meters below the surface. I've never seen that in a groundfish landed from depths of 10-15 meters, which is pretty much the practical limit for where and how I fish from a kayak. [That orange monster was taken from about 20 meters down ... deepest catch I've ever made from a kayak.]
But, the other person made the claim that even fish taken from 10 meters down may, emphasis
may, suffer internal damage which eventually kills them. I have no way to verify that. But, my rule is that everything which comes to the surface gets eaten. If the luck of the draw provides three little ones, that's it. If the first one is big enough for dinner, that's it for the day.
In some popular kayaking areas (Broken Group, for example), the taking of groundfish is now prohibited, to allow stocks to recover. I believe that is a DFO restriction, and not a voluntary one at all.