The only reason I could see them making a law like that would be if the mortality rate of released fish were high. Not sure what scientific proof they have to justify any increased mortality but gut instint tells me that stressing out the fish or pulling them out of deep water too fast is not really good for the fish.
I have conducted some limited experiments on crappie that I caugth in deep water and some of them lived and some of them died on me.
One thing that did seem to help is putting the caught fish in colder water. I rigged up a system where I could add a pipe to the intake of my livewells water supply sytem and bring the water from the 5 ft below the surface into my livewell instead of the water at the surface. There is about a 5 deg temp difference between the two levels and the colder water seemed help keep the fish better. I could add a ten ft long pvc pipe and bring water from 10ft below the surface if I want too. I am able to stick a 90 deg pvc elbow in my intake hole in the back of my boat's transom and then two shore pieces of clear vinyl tubing I can connect a 1/2" diameter pvc pipe to the intake and have it other end 5 to 10ft down below the water's surface. That really seems to help keep the fish better.
Lots of fish that are caught may or may not die later. It's hard to tell unless we could tag and monitor them over a weeks period of time. Sometimes just touching their skin can remove the slime coating that protects them from fungus or other disease and they may succomb to a disease a few days or weeks later. I have not read where anyone had really studied this well. It may have been done but I just am not aware of the study yet.
Been keeping several live crappie in an aquarium for more than a year now 15 months now and had a few die from fungus disease and the ohters are still doing good.
Originally Posted by Deacon