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I just read a Michigan DNR report which studied lake trout release mortality in Lakes Superior and Huron. Interesting results.

Since Lake Huron is quite similar to Lake Michigan it better approximates our conditions than Lake Superior.

The report concludes surface water temperatures have a great deal to do with whether a trout will survive catch and release. They set the breaking point at 50 or greater, 50 degrees or less. (No explanation of why that division but still surprising results. )

They said a laker released at the surface in water over 50 degrees has a 61% chance of dying from the experience. I’m not all that surprised with that figure. The figure I am surprised at is they have a 43% chance of dying in when released when surface temps are 50 or below.

Sure, there are other mortality causing traumas dished out to a trout other than water temperatures. Still, it gives cause for thought.

One thought is if 53 degrees, upper 50s or warmer temps are bad, just think of how hard on a fish it is this time of year with our surface water in the 70s. Might as well whack ‘em on the head, then throw them back, I’d guess.

I know many anglers don’t like to keep lake trout and sometimes, it’s hard to prevent them from biting a lure you are dangling to tempt a salmon or steelhead. However, I know some guys drop one or more lures down close to the bottom and use the type of lures (spin n glows) to occasionally hook a trout to break up the monotony while waiting to hook the next silver-fish.

Catch a truly “accidental” trout and do with it what you wish. Toss it back if you wish - at least it has a chance, even if it’s slim, of surviving. Better than tossing it in the trash back on land. None will survive that. On the other hand, some may want to think twice about trying to catch a trout just for the fun of it and then tossing it back so they don’t have to further mess with it.

I’m not against C&R fishing. I release lots of fish I catch when I’m not on Lake Michigan and when I’m sure they have a reasonably good chance of survival. I know it’s not 100% but I’d like to think C&R survival is 90% or better. I’d rethink C&R fishing if I thought half of the catch or more is doomed, just for the sport of it.

Good food for thought Mike.

I have the paper on my desk right now.

For Lake Huron, if surface temps were below 50 degrees, there was 52% mortality (but a very low sample size, so not a terribly precise estimate. It's likely that the real number is lower than this). For surface temps 50-60, there was 45% mortality. For surface temps over 61 degrees, there was 76% mortality. Most of the angler catch on Lake Huron is when surface temps are above 50 degrees, so hard to make a comparison between temperature bins when there is low sample size in the colder bin

Lake Superior is a different story though, if surface temps are below 50, there was only 15% mortality. They had a really good sample size here, so it's probable that the Lake Huron number is similar to this if they had much larger sample size. Lake Superior also had 43% mortality between 50 and 60 degrees, and 43% above 61 degrees.

The authors note that Lake Superior's upper temp ranges were really not that much above 63-66 degrees, whereas many of the Lake Huron trout were released in temps 67-75 degree surface temps. My inference from the data is that mortality may increase very gradually from 55-65 degrees, but once you get into a 15+ temp difference, mortality skyrockets. Most salmon and trout species exhibit physiological stress just existing in water temps approaching 70, much less being subjected to the stress of getting caught


Taken together, it's pretty clear that under 50 is pretty good for releasing them, 50-65 is a coin flip, and anything over 65 degrees is a likely a dead fish - certainly if its 70 and up.

They chose the under 50, 50-60, and 61 and up temperature bins because the lake trout's preferred thermal regime is 48-52 degrees. It's stressful for fish to go through rapid temp change, which is why they examined 3 general scenarios of not much temperature change, medium temp change, and extreme temp change. Data aligns pretty well with common sense, which is always nice.



On a personal note, I'll C&R lakers all day long in surface water temps under 50 degrees, (generally October-April) especially if they are caught 60 feet and shallower. But they go in the box if they are caught incidentally between May-September

Thanks, Ben. I appreciate your insight. From personal experience, I think one of the differences in Lake Superior and Huron and the 50 degree over/under thing is at the places I’ve fished in Superior - June through September in different trips, even when the surface temperature was in the 60s (never saw 70) the “warm” surface layer was only a few feet thick. Down 10 to 20 feet, it was 40s and 50s and though I’ve caught Superior trout 100 feet deep, most of them I’ve caught were 50 feet or shallower. One late June trip out of Duluth the star lures were Long-A Bombers run with no weight behind planer boards. Those probably don’t troll more than 5 or 6 feet deep.

What I’m leading up to here is the additional stress (not specifically addressed in this research) of barotrauma - which happens when fish are pulled to the surface from way-down-dare. LTs can burp the gas out of their swim bladder but they don’t do it regularly. You can tell if they’ve burped pretty easy when you are pulling them in.

When you are reeling in a trout if it stops fighting half way to the surface and becomes dead weight - usually planing to the top 50 or 60 feet back of the boat, it’s not burped and its swim bladder is pressing on the rest of its innards almost paralyzing it. Turn that fish loose or have it come unhooked and it will float like a balloon. If it’s floating in 74 degree water, it’s cooking and will probably become seagull fodder.

On the other hand, just yesterday I had a couple of trout come up behind my boat, still fighting hard, twisting and resisting and they won the battle. The hooks popped out and in an instant, you could see those fish swimming back to the depths. I’m betting they survived.

One more “experienced” based comment. I’ve had numerous trout coming to the back of the boat, little more than meat on a string, and then when the angler is pulling it the last few feet, the act of bringing it close and pulling it’s head to the surface does two things. One, it revitalizes the fish just enough for it to burp out the gas in its swim bladder. Two, with the head at the surface, you can hear the burp! Usually, a little burp at first, but as the gas releases, the fish becomes un-paralyzed and flips its head back and forth and you can hear another two or three burps as more gas is expelled.

If it’s a smaller sized trout, it may still be burping in the net and rolling around making it hard to unhook and pull out of the net. If it’s a larger sized trout, chances are it will be energized enough to actually swap ends, pull out some drag and make the angler work a bit to get it back into netting range.

My guess is if you can get a “self-burping” trout in and out of the net quickly and release it, regardless of the surface temperature, it will have a fair shot at being able to dive down to the depths where it can survive. Hopefully, there are researchers out there paying as much attention to barotrauma on trout as they are surface temperatures.