It said it had a bite taken out of it,so I'd assume natural selection....ie: slow swimmer maybe.

Not sure what you do, but I keep what I catch, if it's legal.
Have tried a couple of times to return big fish (seldom catch monsters...) without luck.
I love the sport of fishing, but I'm not good enough to catch them purely for sport.
So, if on any given day I'm lucky enough to catch 5, I keep them so long as of legal size, I don't return small legal fish 'hoping to catch something bigger' and when I have enough, I stop.

We catch starting out.. if legal, goes in the bin.. till we have a feed for each family. From then its more a recreational attitude type day.. few more for the smoker.
Only brought a legal bin in 2x .
One gets to enough for a feed, some for the neighbours then what goes in the bin is more selective... smoke likes bigger fillets, plates like pannies.
 Most of our fishing is in the 3 to 35 m range.
shallow is not an issue for release, unless swallow/ gut hooked.
 These if legal alway hit the bin.
 Deeper water means usually heavier gear.. heavier gear usually means bit more skull drag and blowing the internals.
 One knows when a big fish hits...enough in the bin, so its time to have a bit of fun..and take the time to enjoy, improve on ones fishing skills, avoid pulling a hook... and try and avoid the skull drag bloating of the fish.
Most times it works , some times it doesnt..

 Find there is always a lot of satisfaction being able to return have a fish swim back down, espec a large one.
Add that onto the top of a good fight to get it to the surface... and they tend to fight near all the way up, rather than roll over 1/2 way then float the rest of the way up.
Memorable

To have a fish you would like to release , not want to do so, or even suspect it will not survive takes the edge off a good fight

This describes it very well

but I usually catch them in 40 metres plus and they are toast on hitting the surface, much like a hapuka. I really don't want to catch the bloody things!