**I doubt that DWR has conducted any definitive studies about the mortality rate. But, they have an official position and they have set the rules to cover ALL POSSIBLE SITUATIONS. **
It is tough to write regulations that address every little potential variable. Like you say, many anglers do not have sonar, or know how to use it properly. So, if the rule was that all perch caught from deeper than 20 feet must be released, and a guy had his sonar set wrong, he could be keeping or releasing fish wrong…and be subject to a ticket. And, no matter what the precise wording of the regs, there will always be someone who will try to weasel a way around it.
**Nope, I do not believe that there is a significant mortality rate for perch released even in deeper water. I have conducted my own research and have been part of other studies in other states…and on several species that all show that many fish caught from deeper water DO survive. **
Some of these experiments have included the use of the weighted release devices. Others have included “fizzing”. In fact, we had one “official” (DWR rep present) survey on Deer Creek, when it was first opened to ice fishing. It is illegal for anglers to mark released fish, but the DWR guy supervised the fizzing, marking (fin clips) and release of deep water perch. We not only caught the same fish more than once on that first trip, but recaught many other fin clipped fish from that area over the next few weeks. And…a lot of the “fizzing” was simply poking the point of the hook into the protruding air bladder and sending the fish back down. They usually powered on down without problems…and as stated, many lived to munch our hooks again later. Not 100% mortality.
**Other states have conducted studies on rapid depressurization among different fish species. It is universally agreed that there is a serious change in blood gasses and in some cases even permanent organ or tissue damage…variable by species, total change in pressure and length of time before being repressurized. Some wimpy species, like crappie, seldom survive even if sent back down with a weighted release device. Others, like perch, just sulk for a few minutes and then go back to eating. **
I have read a lot of things, written by both biologists and simple anglers on the subject of the mortality rate of fish that are yanked from deeper water. Their “findings” and opinions go all over the map…from 100% mortality to virtually zero mortality under the right conditions. To me, it is kinda like religion or politics…a matter of personal opinion…based upon the sum total of one’s individual study and experiences.
In this case, we must abide by the prevailing opinion of those who make the regulations. If their opinion is that we save more perch by mandatory keeping, than by culling or even releasing all we catch, then that is the law and we must accept it.
**Let’s just be thankful that DWR does not tell us all that we have to vote for Hillary. (Sorry, Hillary fans. Just making a point) **