Update: the crappie are new. One of the neighborhood kids apparently put some adults in at an unspecified time in the recent past. I finally caught one on a jig, too, but it's obviously second generation.
So there goes the hope that they were there all along or that they were hybrids stocked by someone with (some) sense.
I guess we'll see how it goes (they don't exactly seem to be thriving), but I'll start saving pennies for a barrel of rotenone.
