Smallmouth mystery

Recently caught a large smallie in northern Wisconsin. While I had it in the livewell in between pictures she left these in there for me. They look like calcium deposits or something like that. The smaller ones would crumble in your fingers and they were white on the inside. The ones pictured are rock hard....

Looks like dried peas. Maybe left over from ice fishing. Old timer trick is to drop a bunch of peas around your hole. When the fish comes up to take a pea, you grab em!

19.5" 5 pounds 9 ounces. 15"+ girth

Looks like a 20 incher? 

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They are all the same shape. Like a half circle just different sizes. Definitely came out of the back side of her. There was probably fifteen of them in the livewell. I kept the biggest ones. The largest one is maybe 3-4mm in diameter

My guess is that it's the exoskeleton of crayfish or parts of something that it's eating that the fish is unable to digest. It's definitely not seeds. More like a stone or hard deposit.