Large, overnight Crappie die-off. Reasons?

Hi guys,

I've been gone for quite a while because life got in the way of fishing. But I'm re-visiting because I need your advice, ideas and help.

Two days ago our lake experienced a very large die-off of crappie. At first we thought it was all fish, but as we began pulling them out of the water we realized they were just crappie (none of the other major species -- largemouth bass, northern pike, bluegill, perch -- in the lake died, just the crappie). The dead crappie were all 9"+, no little ones. I estimate we "harvested" about 250 fish. They all looked basically healthy; no apparent fungus or such (not that I'd know what to look for anyway).

A few particulars about the lake: 100 acres, 9ft average depth, in northern Illinois. Last summer we had an aglae explosion due to the drought. Winter was brutal with thick ice and snow cover on the lake for far longer than usual. This summer's been beautiful but the water was pea soup with algae by mid-July. Fishing for all species as been slower than usual this summer.

I only mention the algae because it's really the only change to lake in the last 7-10 years. No new sources of run-off that we know about or other possible causes we can think of.

I'd really appreciate any thoughts or leads you guys have on the possible cause.

Thanks,
Bob

Most likely this was an effect of the algae and decreased oxygen levels in the water. Perhaps crappie are more susceptible to this than the other species? I know largemouth and catfish can tolerate lower oxygen levels than many species and that is why they thrive in shallow warm water along with many sunfish. When algae dies the cells sink and are broken down by bacteria as they decay. This breakdown process requires oxygen and can create a biological oxygen demand. Increases in biological oxygen demand result in decreases of dissolved oxygen concentration in the water. More dying algae means more oxygen is being used for that process rather than remaining in the water. This can have a negative impact on aquatic life and can even cause fish kills. Fish will normally seek new areas in a body of water when oxygen levels change. Given your lake averages 9 ft they probably were very limited on what refuge they could find. My guess, the poor little guys were suffocated :(

Dang that sucks. Our lakes are exactly as you described yours pea soup , the association decided they could manage the lakes better or just as good as the professionals . Not even close, both lakes have plenty of deeper water 20-22 along the main channel and 35' plus near the dams. So hopefully we don't have another fish kill. We lost several hundred over the winter on both lakes. I hoping all this rain will help the clarity and add much needed oxygen. Last time I was out (early last week) the thermocline was around 13-15 feet . But man the lakes are sloooowwww this year . Hope it turns around for you

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Originally Posted by Gobob

Dang that sucks. Our lakes are exactly as you described yours pea soup , the association decided they could manage the lakes better or just as good as the professionals . Not even close, both lakes have plenty of deeper water 20-22 along the main channel and 35' plus near the dams. So hopefully we don't have another fish kill. We lost several hundred over the winter on both lakes. I hoping all this rain will help the clarity and add much needed oxygen. Last time I was out (early last week) the thermocline was around 13-15 feet . But man the lakes are sloooowwww this year . Hope it turns around for you

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What do you use to determine the depth of the thermocline?
Is that information useful in finding the fish.

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Originally Posted by RMGeorge

What do you use to determine the depth of the thermocline?
Is that information useful in finding the fish.

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You can see it on a good di, si, or sonar unit. It will show up as a distinct fuzzy line. Attachment 172297Attachment 172298Attachment 172299To answer your question, knowing the depth of the thermocline is VERY important during the summer months, as the crappie will never be below it. Most times they will be right on top of it, or suspended slightly above it.

Thanks, C.J. My boat came with the most basic fish/depth finder. Your images look awesome to me.

Thanks Cmj could not have done it better. In the summer if you can find a spot that is spring fed or is an inlet and it is at the thermocline or a touch deeper you should find the fish We have a spot or two in our lake at the right depth and there are springs bringing in cooler water so they tend to congregate there. Honey hole sweet spot whatever you want to call it. But we lack structure so they tend to be nomads and cruise ,visit spring and move back out

Good info to know!

Algae blooms are caused by large amounts of nutrient run off going into the water. It happened here on our local lake of a few thousand acres. All the big rains in July here washed in manure from farm fields.

When the water is hot,
The "cline" will show you where they are not....once you can find it I set depths a foot or two above it and try to stay in that depth. Doesn't matter if you're trolling pushing or just slip bobbers over structure. It's a great piece of info to have.